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✍️ Episode References
Reports on Progress in Physics
https://iopscience.iop.org/journal/0034-4885 (https://iopscience.iop.org/journal/0034-4885)
Nature
https://www.nature.com/nature/ (https://www.nature.com/nature/)
Nature Astronomy
https://www.nature.com/natureastronomy/ (https://www.nature.com/natureastronomy/)
Become a supporter of this podcast: https://www.spreaker.com/podcast/spacetime-space-astronomy--2458531/support (https://www.spreaker.com/podcast/spacetime-space-astronomy--2458531/support?utm_source=rss&utm_medium=rss&utm_campaign=rss) .
00:00 This is Space Time Series 28, Episode 65 for broadcast on 30 May 2025
01:00 New theory of gravity
12:15 The Moon's thermal characteristics
22:30 Discovery of white dwarf pulsars
30:00 Skywatch: June night skies and the Taurids meteor shower
Episode link: https://play.headliner.app/episode/27388799?utm_source=youtube
00:00:00 --> 00:00:03 This is Spacetime Series 28, episode 65
00:00:03 --> 00:00:05 for broadcast on the 30th of May,
00:00:05 --> 00:00:09 2025. Coming up on Spacetime, a new
00:00:09 --> 00:00:11 theory of gravity which brings the long
00:00:11 --> 00:00:13 sought after theory of everything closer
00:00:13 --> 00:00:16 to reality. Is there a hot side to the
00:00:16 --> 00:00:18 moon? And astronomers discover white
00:00:18 --> 00:00:22 dwarf pulsars for the first time. All
00:00:22 --> 00:00:26 that and more coming up on Spaceime.
00:00:26 --> 00:00:30 Welcome to Spaceime with Stuart Garry.
00:00:30 --> 00:00:37 [Music]
00:00:45 --> 00:00:47 Scientists have developed a new theory
00:00:47 --> 00:00:49 of gravity which brings the long sought
00:00:49 --> 00:00:51 after theory of everything just a little
00:00:52 --> 00:00:54 bit closer to reality. A quantum theory
00:00:54 --> 00:00:56 of gravity would clear the path to
00:00:56 --> 00:00:58 answering some of the biggest questions
00:00:58 --> 00:01:01 in physics. The study detailed in the
00:01:01 --> 00:01:03 journal reports on progress in physics
00:01:03 --> 00:01:05 claims a unified theory combining
00:01:05 --> 00:01:07 gravity with the other fundamental
00:01:07 --> 00:01:09 forces of nature that's electromagnetism
00:01:09 --> 00:01:11 and the strong and weak nuclear forces
00:01:11 --> 00:01:14 may well at long last be within reach.
00:01:14 --> 00:01:16 Bringing gravity into the fold has been
00:01:16 --> 00:01:18 the goal of generations of physicists
00:01:18 --> 00:01:20 who have struggled to reconcile the
00:01:20 --> 00:01:22 incompatibility of the two cornerstones
00:01:22 --> 00:01:24 of modern physics, namely quantum field
00:01:24 --> 00:01:27 theory and Albert Einstein's theory of
00:01:27 --> 00:01:29 general relativity. The key has been
00:01:29 --> 00:01:31 developing a new quantum theory of
00:01:31 --> 00:01:34 gravity which describes gravity in ways
00:01:34 --> 00:01:35 compatible with the standard model of
00:01:35 --> 00:01:38 particle physics, the cornerstone of our
00:01:38 --> 00:01:40 understanding of the universe. And in
00:01:40 --> 00:01:42 the process, it's opening the door to an
00:01:42 --> 00:01:44 improved understanding of how the
00:01:44 --> 00:01:46 universe began. While the world of
00:01:46 --> 00:01:48 theoretical physics may seem remote from
00:01:48 --> 00:01:51 applicable technology, the findings are
00:01:51 --> 00:01:53 remarkable. See, modern technology is
00:01:53 --> 00:01:55 built on fundamental advances. For
00:01:55 --> 00:01:58 example, the GPS in your smartphone
00:01:58 --> 00:02:00 works thanks to Albert Einstein's theory
00:02:00 --> 00:02:02 of gravity. The study's authors Miko
00:02:02 --> 00:02:05 Partanan and Julie both from Alto
00:02:05 --> 00:02:07 University say that within a few years a
00:02:07 --> 00:02:10 new hypothesis may well unlock crucial
00:02:10 --> 00:02:12 understanding. Now if it does turn out
00:02:12 --> 00:02:14 to lead to a complete quantum field
00:02:14 --> 00:02:16 theory of gravity then eventually it'll
00:02:16 --> 00:02:18 give answers to the very difficult
00:02:18 --> 00:02:20 problems of understanding singularities
00:02:20 --> 00:02:22 the center of black holes and even
00:02:22 --> 00:02:24 understanding the big bang of creation
00:02:24 --> 00:02:27 itself. However, we're not there yet.
00:02:27 --> 00:02:29 Some fundamental questions of physics
00:02:29 --> 00:02:31 still remain under this so-called theory
00:02:31 --> 00:02:33 of everything. For example, current
00:02:33 --> 00:02:35 theories still can't explain why there's
00:02:35 --> 00:02:36 more matter than anti-atter in the
00:02:36 --> 00:02:38 observable universe. And they still
00:02:38 --> 00:02:40 don't know what dark energy and what
00:02:40 --> 00:02:43 dark matter really are. The key to this
00:02:43 --> 00:02:45 new hypothesis was finding a way to
00:02:45 --> 00:02:47 describe gravity in a suitable gauge
00:02:47 --> 00:02:49 theory. A kind of theory in which
00:02:49 --> 00:02:50 particles interact with each other
00:02:50 --> 00:02:52 through a field. Now, the most familiar
00:02:52 --> 00:02:54 gauge field is the electromagnetic
00:02:54 --> 00:02:57 field. Ki says that when electrically
00:02:57 --> 00:02:58 charged particles interact with each
00:02:58 --> 00:02:59 other, they interact through the
00:02:59 --> 00:03:01 electromagnetic field which is the
00:03:01 --> 00:03:04 permanent gauge field. So when particles
00:03:04 --> 00:03:06 have energy, the interactions they have
00:03:06 --> 00:03:07 just because they have energy would
00:03:07 --> 00:03:10 happen through the gravitational field.
00:03:10 --> 00:03:12 But a challenge long facing physicists
00:03:12 --> 00:03:14 is finding a gauge theory for gravity.
00:03:14 --> 00:03:16 One that's compatible with the gauge
00:03:16 --> 00:03:18 theories of the other three fundamental
00:03:18 --> 00:03:19 forces. The electromagnetic force, the
00:03:19 --> 00:03:21 weak nuclear force, and the strong
00:03:21 --> 00:03:23 nuclear force. The standard model of
00:03:23 --> 00:03:25 particle physics is itself a gauge
00:03:25 --> 00:03:27 theory which describes those three
00:03:27 --> 00:03:30 forces and has certain symmetries. The
00:03:30 --> 00:03:32 tenant says the main idea is to have a
00:03:32 --> 00:03:35 gravity gauge theory with a symmetry
00:03:35 --> 00:03:36 that's similar to the standard model
00:03:36 --> 00:03:38 symmetries. Instead of basing the theory
00:03:38 --> 00:03:41 on the very different kind of space-time
00:03:41 --> 00:03:43 symmetry involved in Einstein's general
00:03:43 --> 00:03:45 relativity. Without such a hypothesis,
00:03:46 --> 00:03:47 physicists couldn't reconcile our two
00:03:48 --> 00:03:49 most powerful theories, quantum field
00:03:49 --> 00:03:52 theory and general relativity. Quantum
00:03:52 --> 00:03:54 field theory describes the world of the
00:03:54 --> 00:03:56 very small, tiny particles interacting
00:03:56 --> 00:03:59 in probabilistic ways. On the other
00:03:59 --> 00:04:01 hand, general relativity describes the
00:04:01 --> 00:04:03 grand physics of the cosmic world, the
00:04:03 --> 00:04:05 universe as a whole. So, they're both
00:04:05 --> 00:04:07 descriptions of our universe, but from
00:04:07 --> 00:04:09 very different perspectives. And both
00:04:09 --> 00:04:11 theories have been confirmed with
00:04:11 --> 00:04:12 extraordinary precision, yet they're
00:04:12 --> 00:04:14 still incompatible with each other. And
00:04:14 --> 00:04:16 because gravitational interactions are
00:04:16 --> 00:04:18 weak, more precision's needed in order
00:04:18 --> 00:04:20 to study true quantum gravity effects
00:04:20 --> 00:04:22 beyond general relativity. Tanninsan
00:04:22 --> 00:04:24 says a quantum theory of gravity is
00:04:24 --> 00:04:26 needed in order to understand what kind
00:04:26 --> 00:04:28 of phenomena there are in cases where
00:04:28 --> 00:04:30 there's a gravitational field with high
00:04:30 --> 00:04:31 energies. The sort of conditions you'd
00:04:31 --> 00:04:33 find around black holes and very early
00:04:34 --> 00:04:36 in the universe's existence just after
00:04:36 --> 00:04:38 the big bang. And they're the sort of
00:04:38 --> 00:04:40 places where existing theories of
00:04:40 --> 00:04:42 physics all stop working. Although the
00:04:42 --> 00:04:44 hypothesis is promising, the authors
00:04:44 --> 00:04:46 point out they've not yet completed its
00:04:46 --> 00:04:49 proof. It uses a technical procedure
00:04:49 --> 00:04:51 known as renormalization. That's a
00:04:51 --> 00:04:53 mathematical way of dealing with the
00:04:53 --> 00:04:54 infinities that show up in the
00:04:54 --> 00:04:57 calculations. Now, so far the authors
00:04:57 --> 00:04:59 have shown that while this works up to a
00:04:59 --> 00:05:00 certain point for so-called first order
00:05:00 --> 00:05:03 terms, they yet to make sure that these
00:05:03 --> 00:05:04 infinities can be eliminated throughout
00:05:04 --> 00:05:06 the entire calculation. You see, if
00:05:06 --> 00:05:08 reormalization doesn't work for higher
00:05:08 --> 00:05:10 order terms, you'll get infinite
00:05:10 --> 00:05:12 results. So it's vital to show that this
00:05:12 --> 00:05:15 renormalization continues to work and
00:05:15 --> 00:05:16 therefore they still need to make a
00:05:16 --> 00:05:19 complete proof. Nevertheless, it's
00:05:19 --> 00:05:23 fascinating work. This spaceime still to
00:05:23 --> 00:05:25 come. Is there a hot side to the moon?
00:05:26 --> 00:05:28 And astronomers discover their first
00:05:28 --> 00:05:30 white dwarf pulsars. All that and more
00:05:30 --> 00:05:33 still to come on Spaceime.
00:05:33 --> 00:05:35 [Music]
00:05:35 --> 00:05:37 Today's episode of Spaceime is brought
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00:06:12 --> 00:06:14 sideways. And here's the kicker. You
00:06:14 --> 00:06:16 don't even have to aim. Just press
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00:06:23 --> 00:06:25 Want to follow your movement, lock onto
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00:06:28 --> 00:06:31 Well, now that's just a few taps away.
00:06:31 --> 00:06:33 And for those epic how on earth do you
00:06:33 --> 00:06:35 film that shots? The invisible selfie
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00:06:38 --> 00:06:39 from the footage, giving you that
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00:07:37 --> 00:07:44 spacetime. And now it's back to our
00:07:44 --> 00:07:48 [Music]
00:07:48 --> 00:07:51 show. A new study claims the moon's near
00:07:51 --> 00:07:53 earth-facing side is actually hotter
00:07:53 --> 00:07:55 than its far side. The findings are
00:07:55 --> 00:07:57 reported in the journal nature based on
00:07:57 --> 00:07:59 data from NASA's Grail spacecraft and
00:07:59 --> 00:08:01 the twin eb and flow spacecraft which
00:08:01 --> 00:08:03 have been studying the moon from orbit.
00:08:03 --> 00:08:06 Our moon is gravitationally tidly locked
00:08:06 --> 00:08:08 to the earth. That means the same side
00:08:08 --> 00:08:10 always faces our planet. Even more
00:08:10 --> 00:08:13 fascinating is the dichotomy of the moon
00:08:13 --> 00:08:15 which has long intrigued scientists. You
00:08:15 --> 00:08:17 see there are notable differences in
00:08:17 --> 00:08:20 geology, volcanism and custal thickness
00:08:20 --> 00:08:23 between the lunar near and far sides.
00:08:23 --> 00:08:25 The moon's near side appears darker and
00:08:25 --> 00:08:27 it's dominated by smooth ancient lava
00:08:27 --> 00:08:29 flows indicating a high concentration of
00:08:29 --> 00:08:32 volcanism. On the other hand, the far
00:08:32 --> 00:08:34 side is far more rugged. The new study
00:08:34 --> 00:08:36 using data from Grail suggests that this
00:08:36 --> 00:08:39 dichotomy is caused by 2 to 3%
00:08:39 --> 00:08:41 difference in the lunar mantle's ability
00:08:41 --> 00:08:43 to deform on each side. The author
00:08:43 --> 00:08:45 suggested the reason is that the moon's
00:08:45 --> 00:08:49 near side mantle is up to 170° C hotter
00:08:49 --> 00:08:51 than its far side. It's thought this
00:08:51 --> 00:08:52 thermal difference could be caused by
00:08:52 --> 00:08:54 the radioactive decay of thorium and
00:08:54 --> 00:08:56 titanium within the moon's near side,
00:08:56 --> 00:08:58 which could be a remnant of the volcanic
00:08:58 --> 00:09:00 activity that formed the near side
00:09:00 --> 00:09:02 surface between 3 and 4 billion years
00:09:02 --> 00:09:04 ago. The authors say the same methods,
00:09:04 --> 00:09:06 which have now being used to study the
00:09:06 --> 00:09:08 moon's interior from orbit, could also
00:09:08 --> 00:09:09 be used to measure differences in the
00:09:09 --> 00:09:11 structure of other planetary bodies,
00:09:11 --> 00:09:13 such as the red planet Mars, the
00:09:13 --> 00:09:15 Saturnian moon Enceladus, and the Jovian
00:09:15 --> 00:09:19 moon Ganymede. This is spacetime. Still
00:09:19 --> 00:09:21 to come, astronomers discover a white
00:09:21 --> 00:09:24 dwarf star acting like a pulsar and the
00:09:24 --> 00:09:26 June solstice, the constellation
00:09:26 --> 00:09:28 Sagittarius, and the torids meteor
00:09:28 --> 00:09:30 shower are among the highlights of the
00:09:30 --> 00:09:34 June night skies on Skywatch.
00:09:34 --> 00:09:47 [Music]
00:09:47 --> 00:09:49 A white dwarf and a red dwarf have been
00:09:49 --> 00:09:50 discovered closely orbiting each other
00:09:50 --> 00:09:54 and emitting radio pulses every 2 hours.
00:09:54 --> 00:09:56 Findings reported in the journal Nature
00:09:56 --> 00:09:58 Astronomy mean that neutron stars are no
00:09:58 --> 00:10:00 longer the only stellar bodies that emit
00:10:00 --> 00:10:03 such pulses. Now, a key factor in this
00:10:03 --> 00:10:05 discovery could be the way the binary
00:10:05 --> 00:10:07 pair is spaced unusually far apart from
00:10:07 --> 00:10:09 each other. Thanks to follow-up
00:10:09 --> 00:10:11 observations using optical and X-ray
00:10:11 --> 00:10:13 telescopes, the study's authors were
00:10:13 --> 00:10:14 able to determine the origin of these
00:10:14 --> 00:10:16 pulsars coming from this binary system
00:10:16 --> 00:10:18 with certainty. The findings are
00:10:18 --> 00:10:20 important because they're hoping to
00:10:20 --> 00:10:21 explain the sources of these strange
00:10:21 --> 00:10:23 radio emissions which are found right
00:10:23 --> 00:10:27 across the Milky Way galaxy. This is
00:10:27 --> 00:10:42 [Music]
00:10:42 --> 00:10:44 spaceime. And time now to check out the
00:10:44 --> 00:10:46 night skies of June on
00:10:46 --> 00:10:49 Skywatch. June is the fourth month of
00:10:49 --> 00:10:50 the old Roman calendar. and it's named
00:10:50 --> 00:10:53 after Juno who was the wife of Jupiter
00:10:53 --> 00:10:54 is also the equivalent to the Greek
00:10:54 --> 00:10:57 goddess Hera. Another belief is that the
00:10:57 --> 00:10:58 month's name actually comes from the
00:10:58 --> 00:11:01 Latin word juniors which means younger
00:11:01 --> 00:11:03 ones. It's a great time to look up the
00:11:03 --> 00:11:05 night skies and marvel at the majesty of
00:11:06 --> 00:11:07 the Milky Way as it puts on its
00:11:08 --> 00:11:11 spectacular overhead display. June also
00:11:11 --> 00:11:12 marks the winter solstice in the
00:11:12 --> 00:11:14 Southern Hemisphere, which this year
00:11:14 --> 00:11:16 happens at 12:42 in the afternoon of
00:11:16 --> 00:11:18 Saturday, June the 21st, Australian
00:11:18 --> 00:11:21 Eastern Standard Time. That's 10:42 in
00:11:21 --> 00:11:23 the evening of Friday, June the 20th, US
00:11:23 --> 00:11:26 Eastern Daylight Time, and 2:42 in the
00:11:26 --> 00:11:28 morning of Saturday, June the 21st,
00:11:28 --> 00:11:30 Greenwich Meime. And while it means the
00:11:30 --> 00:11:32 start of winter south of the equator, it
00:11:32 --> 00:11:34 means the arrival of summer for our
00:11:34 --> 00:11:35 lucky listeners in the northern part of
00:11:36 --> 00:11:38 the planet. The June solstice occurs
00:11:38 --> 00:11:40 when the sun reaches its most northerly
00:11:40 --> 00:11:42 point in the sky as seen from Earth.
00:11:42 --> 00:11:44 Zenith appearing to be directly above
00:11:44 --> 00:11:47 the Tropic of Cancer. See, Earth's
00:11:47 --> 00:11:49 seasons are governed by the tilt of the
00:11:49 --> 00:11:51 planet's axis as it journeys around the
00:11:51 --> 00:11:53 Sun. Now, the Earth's axis is always
00:11:53 --> 00:11:55 pointed the same direction in space
00:11:55 --> 00:11:57 regardless of the position of the planet
00:11:57 --> 00:11:59 Earth as it orbits around the Sun. So on
00:11:59 --> 00:12:01 the day of the June solstice, Earth's
00:12:01 --> 00:12:04 south pole is tilted by 23 1/2° away
00:12:04 --> 00:12:06 from the sun, while the north pole is
00:12:06 --> 00:12:08 tilted by the same amount towards the
00:12:08 --> 00:12:11 sun. The sun rising in the northeast and
00:12:11 --> 00:12:13 setting in the northwest. Of course, 6
00:12:13 --> 00:12:15 months later, when the south pole is
00:12:15 --> 00:12:16 tilted towards the sun, it's the
00:12:16 --> 00:12:18 southern hemisphere summer. And in
00:12:18 --> 00:12:20 between, we have the autumn and spring
00:12:21 --> 00:12:23 equinoxes. Temperatures on Earth aren't
00:12:23 --> 00:12:25 determined by Earth's orbital distance
00:12:25 --> 00:12:27 from the Sun, but rather the angle of
00:12:27 --> 00:12:29 the Sun's rays striking the Earth. So,
00:12:29 --> 00:12:32 in summer, the sun's high in the sky and
00:12:32 --> 00:12:33 the rays hit the planet at a steep
00:12:33 --> 00:12:36 angle. In winter, the sun's lower in the
00:12:36 --> 00:12:38 sky and the rays strike the Earth at a
00:12:38 --> 00:12:40 far shallower angle. Now, in most parts
00:12:40 --> 00:12:43 of the world, the seasons begin on the
00:12:43 --> 00:12:45 day of the solstice or equinox. However,
00:12:45 --> 00:12:48 Australia is weird. Here, seasons begin
00:12:48 --> 00:12:50 on the first day of a specific calendar
00:12:50 --> 00:12:52 month. That means the 1st of March for
00:12:52 --> 00:12:54 autumn, the 1st of June for winter, the
00:12:54 --> 00:12:56 1st of September for spring, and you
00:12:56 --> 00:12:58 guessed it, the 1st of December for
00:12:58 --> 00:13:01 summer. Okay, let's check out the stars.
00:13:01 --> 00:13:03 Well, almost overhead this time of the
00:13:03 --> 00:13:06 year, we find the constellation Virgo.
00:13:06 --> 00:13:08 Virgo is named after the goddess of
00:13:08 --> 00:13:10 justice and the harvest in ancient Greek
00:13:10 --> 00:13:12 mythology, who used her scales to weigh
00:13:12 --> 00:13:14 good and evil. However, she became so
00:13:14 --> 00:13:16 disenchanted with the evil deeds of men,
00:13:16 --> 00:13:18 she wound up throwing away her scales
00:13:18 --> 00:13:20 and retreated to the heavens.
00:13:20 --> 00:13:22 Interestingly, the ancient Egyptians
00:13:22 --> 00:13:24 also associate Virgo with agriculture.
00:13:24 --> 00:13:26 There she was the goddess Isis who
00:13:26 --> 00:13:28 sprinkled the heads of wheat across the
00:13:28 --> 00:13:31 sky forming the Milky Way. To science,
00:13:31 --> 00:13:33 Virgo is a tightly packed region
00:13:33 --> 00:13:36 containing some 2 galaxies, all
00:13:36 --> 00:13:38 gravitationally bound into a giant
00:13:38 --> 00:13:40 galaxy cluster some 60 million light
00:13:40 --> 00:13:43 years away. In fact, our own local group
00:13:43 --> 00:13:45 of galaxies dominated by the Milky Way
00:13:45 --> 00:13:47 and Andromeda are outlying members of
00:13:47 --> 00:13:50 this group. The Virgo cluster is at the
00:13:50 --> 00:13:52 heart of what's known as the Virgo
00:13:52 --> 00:13:54 supercluster, a massive galactic node in
00:13:54 --> 00:13:56 the large scale cosmic web-like
00:13:56 --> 00:13:58 structure of the universe. The mass of
00:13:58 --> 00:14:00 the Virgo supercluster is so great that
00:14:00 --> 00:14:03 its gravity generates the Virgo centric
00:14:03 --> 00:14:05 flow, causing our Milky Way galaxy as
00:14:05 --> 00:14:06 well as Andromeda and all the other
00:14:06 --> 00:14:08 members of the local galactic group to
00:14:08 --> 00:14:10 move towards the supercluster at around
00:14:10 --> 00:14:11
00:14:11 --> 00:14:14 km/s. That's despite the accelerating
00:14:14 --> 00:14:16 expansion of the universe over cosmic
00:14:16 --> 00:14:18 time scales. The Virgo supercluster is
00:14:18 --> 00:14:20 now thought to be a lobe on an even
00:14:20 --> 00:14:22 larger galactic supercluster called
00:14:22 --> 00:14:25 Lania, the center of which is known as
00:14:25 --> 00:14:27 the Great Attractor. Despite the Virgo
00:14:28 --> 00:14:30 cluster size, it's so far away from us,
00:14:30 --> 00:14:31 it's hard to see without a decently
00:14:32 --> 00:14:33 sized backyard telescope. You'll need
00:14:33 --> 00:14:35 something at least 100 millimeters in
00:14:35 --> 00:14:38 diameter or larger in order to see it.
00:14:38 --> 00:14:40 Now, if you look directly straight up at
00:14:40 --> 00:14:42 Zenith, you'll see the constellation
00:14:42 --> 00:14:45 Corvis the Crow. Greek mythology tells
00:14:45 --> 00:14:47 us that Corvvis could talk to humans,
00:14:47 --> 00:14:50 but he was a lazy bird and so Apollo
00:14:50 --> 00:14:52 took away his ability to speak and
00:14:52 --> 00:14:53 banished into the
00:14:53 --> 00:14:55 heavens. One of the most spectacular
00:14:55 --> 00:14:57 highlights of the constellations Virgo
00:14:57 --> 00:15:00 and Corvvis is the spectacular sombrero
00:15:00 --> 00:15:02 galaxy M104.
00:15:02 --> 00:15:04 Visible with a good pair of binoculars
00:15:04 --> 00:15:06 or a small backyard telescope, this
00:15:06 --> 00:15:08 stunning spiral galaxy is seen almost
00:15:08 --> 00:15:10 edge on and it will provide you with a
00:15:10 --> 00:15:12 spectacular backlit view of its galactic
00:15:12 --> 00:15:14 bold stars and the molecular gas and
00:15:14 --> 00:15:18 dust lanes in its arms. M104 is located
00:15:18 --> 00:15:21 some 31 million lighty years away and
00:15:21 --> 00:15:23 it's moving away from the Milky Way at
00:15:23 --> 00:15:24 about 1
00:15:24 --> 00:15:27 km/s. A light year is about 10 trillion
00:15:27 --> 00:15:29 km. The distance a photon can travel in
00:15:30 --> 00:15:31 a year at the speed of light, which is
00:15:31 --> 00:15:34 about 300 kilometers/s in a vacuum
00:15:34 --> 00:15:36 and the ultimate speed limit of the
00:15:36 --> 00:15:38 universe. The sombrero galaxy has a
00:15:38 --> 00:15:41 diameter of around 50 light years,
00:15:41 --> 00:15:43 making it about 30% the size of our
00:15:43 --> 00:15:46 Milky Way galaxy. It's surrounded up to
00:15:46 --> 00:15:48 2 globular clusters and it has an
00:15:48 --> 00:15:50 active central super massive black hole
00:15:50 --> 00:15:52 at least a billion times the mass of our
00:15:52 --> 00:15:55 sun. Now, by comparison, Sagittarius A
00:15:56 --> 00:15:57 star, that's the super massive black
00:15:57 --> 00:15:59 hole at the center of our own galaxy,
00:15:59 --> 00:16:01 has just 4.3 million times the sun's
00:16:01 --> 00:16:04 mass. Globular clusters are either the
00:16:04 --> 00:16:06 central remnants of smaller galaxies
00:16:06 --> 00:16:07 cannibalized by larger ones, or
00:16:08 --> 00:16:10 alternatively, they're tight balls
00:16:10 --> 00:16:12 comprising millions of stars, which all
00:16:12 --> 00:16:14 originally formed at the same time in
00:16:14 --> 00:16:16 the same collapsing molecular gas and
00:16:16 --> 00:16:18 dust cloud. By the way, the brightest
00:16:18 --> 00:16:20 star in Virgo is Spyer, a spectroscopic
00:16:20 --> 00:16:23 binary located some 250 lighty years
00:16:23 --> 00:16:26 away. Spectroscopic binaries are stars
00:16:26 --> 00:16:28 that are orbiting so close together they
00:16:28 --> 00:16:29 can only be told apart by their
00:16:29 --> 00:16:31 individual spectrographic
00:16:31 --> 00:16:34 signatures. Now, looking about 20° above
00:16:34 --> 00:16:36 the western horizon early in the evening
00:16:36 --> 00:16:37 this time of the year, you'll find the
00:16:37 --> 00:16:40 fourth brightest object in the sky, the
00:16:40 --> 00:16:43 dog star Sirius. Only the sun, the moon,
00:16:43 --> 00:16:45 and the planet Venus look brighter.
00:16:45 --> 00:16:47 Looking to the northwest or right of
00:16:48 --> 00:16:49 Sirius, you'll find another fairly
00:16:49 --> 00:16:52 bright star, Proion, the brightest star
00:16:52 --> 00:16:55 in Canthis Minor, the lesser dog. In
00:16:55 --> 00:16:57 Greek mythology, Canis Major and Canis
00:16:57 --> 00:17:00 Minor were Orion's hunting dogs. Proon
00:17:00 --> 00:17:03 is a binary star system. It comprises a
00:17:04 --> 00:17:06 spectral type F main sequence white
00:17:06 --> 00:17:08 yellow star, Pron A, and a faint white
00:17:08 --> 00:17:11 dwarf companion, Proion B. Main sequence
00:17:11 --> 00:17:13 stars are those undergoing hydrogen
00:17:13 --> 00:17:16 fusion into helium in their cores.
00:17:16 --> 00:17:18 Astronomers describe stars in terms of
00:17:18 --> 00:17:20 spectral types, a classification system
00:17:20 --> 00:17:22 based on temperature and
00:17:22 --> 00:17:24 characteristics. The hottest, most
00:17:24 --> 00:17:26 massive, and most luminous stars, and
00:17:26 --> 00:17:29 then spectrotype O blue stars. They're
00:17:29 --> 00:17:31 followed by spectrotype B blue white
00:17:31 --> 00:17:34 stars. Then spectrotype A white stars,
00:17:34 --> 00:17:36 spectrotype F, whitish yellow stars,
00:17:36 --> 00:17:38 spectrotype G yellow stars. That's where
00:17:38 --> 00:17:41 our sun fits in. Then there spectral
00:17:41 --> 00:17:43 type K orange stars and the coolest and
00:17:43 --> 00:17:45 least massive known stars are spectral
00:17:45 --> 00:17:48 type M red stars. Now each spectral
00:17:48 --> 00:17:50 classification can also be subdivided
00:17:50 --> 00:17:52 using a numeric digit to represent
00:17:52 --> 00:17:53 temperature with zero being the hottest
00:17:54 --> 00:17:56 and nine the coolest. And then you can
00:17:56 --> 00:17:58 add a Roman numeral to represent
00:17:58 --> 00:18:00 luminosity. Put all that together and
00:18:00 --> 00:18:03 our sun is officially classified as a
00:18:03 --> 00:18:07 G2V or G25 yellow dwarf star. Now also
00:18:07 --> 00:18:09 included in the stellar classification
00:18:09 --> 00:18:12 system are spectrotypes LT and Y which
00:18:12 --> 00:18:14 are assigned to failed stars known as
00:18:14 --> 00:18:16 brown dwarves. Some of which were born
00:18:16 --> 00:18:18 as spectrotype M red stars but became
00:18:18 --> 00:18:20 brown dwarves after losing some of their
00:18:20 --> 00:18:23 mass. Brown dwarves fit into a unique
00:18:23 --> 00:18:24 category between the largest planets
00:18:24 --> 00:18:26 which can be up to 13 times the mass of
00:18:26 --> 00:18:28 say Jupiter and the smallest spectrotype
00:18:28 --> 00:18:31 M red dwarf stars which are around 75 to
00:18:31 --> 00:18:33 80 times the mass of Jupiter or around
00:18:33 --> 00:18:36 0.08 08 solar masses. Now, the other
00:18:36 --> 00:18:38 type of star we just mentioned were
00:18:38 --> 00:18:40 white dwarves. They're the stellar
00:18:40 --> 00:18:43 corpses of sunlike stars. Having used up
00:18:43 --> 00:18:45 all its nuclear fuel supply, fusing
00:18:45 --> 00:18:47 hydrogen into helium, these stars expand
00:18:48 --> 00:18:50 into red giants as they fuse helium into
00:18:50 --> 00:18:53 carbon and oxygen. The sun and stars
00:18:53 --> 00:18:55 like it aren't massive enough to fuse
00:18:55 --> 00:18:58 carbon and oxygen into heavier elements,
00:18:58 --> 00:19:00 so they turn off. Eventually, the outer
00:19:00 --> 00:19:02 gazes envelopes will float off into
00:19:02 --> 00:19:04 space as spectacular objects known as
00:19:04 --> 00:19:07 planetary nebula. What's left behind is
00:19:07 --> 00:19:09 a super dense white hot stellar core
00:19:09 --> 00:19:12 about the size of the Earth. This is the
00:19:12 --> 00:19:14 white dwarf, which will slowly cool over
00:19:14 --> 00:19:18 the Aons. The white dwarf Pro B is about
00:19:18 --> 00:19:21 0.6 times the mass of the sun and has a
00:19:21 --> 00:19:24 diameter of around 8 kilometers.
00:19:24 --> 00:19:27 Located about 11.6 six light years away.
00:19:27 --> 00:19:29 Proon A is about one and a half times
00:19:29 --> 00:19:31 the mass and twice the radius of our
00:19:31 --> 00:19:33 sun. But it also has some seven times
00:19:33 --> 00:19:35 the sun's luminosity. That makes it
00:19:35 --> 00:19:37 unusually bright for a star of this
00:19:37 --> 00:19:39 type. And that suggests that it's now
00:19:39 --> 00:19:41 starting to evolve off the main
00:19:41 --> 00:19:43 sequence, having fused nearly all of its
00:19:43 --> 00:19:46 core hydrogen into helium. So that means
00:19:46 --> 00:19:48 it's slowly expanding out to become a
00:19:48 --> 00:19:51 subgiant as it begins fusing its core
00:19:51 --> 00:19:53 helium into oxygen and carbon and
00:19:53 --> 00:19:55 burning hydrogen further out from the
00:19:55 --> 00:19:57 core. As it continues to expand, the
00:19:58 --> 00:20:00 star will eventually swirl somewhere
00:20:00 --> 00:20:02 between 80 and 150 times its current
00:20:02 --> 00:20:04 diameter in the process becoming a red
00:20:04 --> 00:20:06 or orange giant. This will probably
00:20:06 --> 00:20:09 happen within the next 10 to 100 million
00:20:09 --> 00:20:12 years. The two stars Proon A and B orbit
00:20:12 --> 00:20:15 each other every 40.82 82 Earth years at
00:20:15 --> 00:20:17 an average distance of 15 astronomical
00:20:17 --> 00:20:19 units, about the distance Uranus is from
00:20:19 --> 00:20:21 the Sun. An astronomical unit is the
00:20:21 --> 00:20:23 average distance between the Earth and
00:20:23 --> 00:20:25 the Sun, which is around 150 million
00:20:25 --> 00:20:29 kilometers or 8.3 light minutes. Now,
00:20:29 --> 00:20:31 looking towards the northnorthwest right
00:20:31 --> 00:20:32 now, and you'll see the constellation
00:20:32 --> 00:20:34 Leo the Lion looking like a bunch of
00:20:34 --> 00:20:36 stars shaped like an upside down
00:20:36 --> 00:20:40 question mark. Located just 36.7 lighty
00:20:40 --> 00:20:43 years away, Octurus is a bloated aging
00:20:43 --> 00:20:46 red giant about 7.1 billion years old
00:20:46 --> 00:20:49 and nearing the end of its life. Having
00:20:49 --> 00:20:51 used up all its core hydrogen, it's now
00:20:51 --> 00:20:54 fusing helium into carbon and oxygen.
00:20:54 --> 00:20:56 This has caused the star, which is only
00:20:56 --> 00:20:58 slightly more massive than our sun, to
00:20:58 --> 00:21:00 expand out to around 25 times the sun's
00:21:00 --> 00:21:03 diameter. In the process, becoming about
00:21:03 --> 00:21:06 170 times as luminous. It will soon puff
00:21:06 --> 00:21:08 off its outer gaseous envelope as a
00:21:08 --> 00:21:10 planetary nebula, revealing its white
00:21:10 --> 00:21:12 hot stellar core. Now, in Greek
00:21:12 --> 00:21:15 mythology, Acturus was the guardian of
00:21:15 --> 00:21:17 the bear. Now, this is a reference to it
00:21:17 --> 00:21:19 being next to the constellations Ursa
00:21:19 --> 00:21:21 Major and Ursa Minor, the greater and
00:21:21 --> 00:21:23 lesser bears. Now, there's some
00:21:23 --> 00:21:25 indications that Arcturus could have a
00:21:25 --> 00:21:27 binary stellar companion, but the
00:21:27 --> 00:21:29 results remain inconclusive. There's
00:21:29 --> 00:21:31 also some speculation that it could have
00:21:31 --> 00:21:33 a large planet or substellar object
00:21:33 --> 00:21:35 around 12 Jupiter masses orbiting it.
00:21:35 --> 00:21:37 That's close to brown dwarf size, but
00:21:37 --> 00:21:40 again, the search remains
00:21:40 --> 00:21:42 inconclusive. Now, to the east are the
00:21:42 --> 00:21:43 three brightest stars in the
00:21:44 --> 00:21:45 constellation Libra, the scales of
00:21:45 --> 00:21:47 justice. They're visible about halfway,
00:21:47 --> 00:21:50 about 40° above the horizon. These
00:21:50 --> 00:21:52 represent the claws of Scorpius, the
00:21:52 --> 00:21:54 scorpion, which is chasing a ry across
00:21:54 --> 00:21:57 the sky. The brightest star in the
00:21:57 --> 00:21:59 constellation Scorpius is Alpha Scorpia
00:21:59 --> 00:22:03 or Antares, the Scorpion's heart. Easily
00:22:03 --> 00:22:05 seen with the unaded eye, this red super
00:22:05 --> 00:22:07 giant some 550 light years away. And
00:22:08 --> 00:22:09 it's one of the largest known stars in
00:22:09 --> 00:22:12 the universe. It has about 18 times the
00:22:12 --> 00:22:15 mass and 883 times the diameter of our
00:22:15 --> 00:22:17 sun. And it has some 10 times more
00:22:17 --> 00:22:20 luminosity than our sun. Now looking to
00:22:20 --> 00:22:22 the southeast now and you'll see the
00:22:22 --> 00:22:25 constellation Sagittarius, the archer.
00:22:25 --> 00:22:27 Sagittarius marks the direction of the
00:22:27 --> 00:22:29 center of our galaxy, the Milky Way.
00:22:29 --> 00:22:32 It's located 26 lighty years away
00:22:32 --> 00:22:33 and is home to the galaxy's super
00:22:33 --> 00:22:37 massive black hole, Sagittarius a star.
00:22:37 --> 00:22:39 To the ancient Babylonians, Sagittarius
00:22:39 --> 00:22:41 was the god Nurgal, the centaur, a
00:22:41 --> 00:22:43 creature that was half man and half
00:22:43 --> 00:22:45 horse. By the time Greek mythology took
00:22:45 --> 00:22:48 over, Sagittarius was carrying his bow
00:22:48 --> 00:22:49 loaded with an arrow pointing towards
00:22:49 --> 00:22:52 Antares, the heart of Scorpius, the
00:22:52 --> 00:22:54 Scorpion. The center of the Milky Way
00:22:54 --> 00:22:56 galaxy, and its super massive black
00:22:56 --> 00:22:58 hole, Sagittarius A star, lie in the
00:22:58 --> 00:23:00 westernmost part of the constellation
00:23:01 --> 00:23:02 Sagittarius. One of the brightest stars
00:23:02 --> 00:23:05 in Sagittarius is Alpha Sagittaria or
00:23:05 --> 00:23:07 Rockbat, meaning the arch's knee. A
00:23:07 --> 00:23:11 spectral type B blue star located 182
00:23:11 --> 00:23:12 lighty years away. It is some two and a
00:23:12 --> 00:23:14 half times the diameter of the sun and
00:23:14 --> 00:23:17 it's about 40 times as luminous.
00:23:17 --> 00:23:18 Astronomers think it's surrounded by a
00:23:18 --> 00:23:20 dense debris disc and a newborn
00:23:20 --> 00:23:22 companion star which is only just
00:23:22 --> 00:23:24 joining the main sequence. Now the
00:23:24 --> 00:23:27 overall brightest star in Sagittarius or
00:23:27 --> 00:23:29 Calstralus, the southern part of the
00:23:29 --> 00:23:31 bow. Epsilon Sagittarius is a binary
00:23:32 --> 00:23:34 star system located 143 light years
00:23:34 --> 00:23:36 away. The primary star is an evolved
00:23:36 --> 00:23:39 spectrotype E blue giant now at the end
00:23:39 --> 00:23:41 of its life on the main sequence. It has
00:23:41 --> 00:23:43 about three and a half times the sun's
00:23:43 --> 00:23:45 mass, almost 7 times its radius, and
00:23:45 --> 00:23:48 it's radiating around 363 times the
00:23:48 --> 00:23:51 sun's luminosity. It's also a very
00:23:51 --> 00:23:53 strong X-ray source, and it's spinning
00:23:53 --> 00:23:55 incredibly rapidly with an estimated
00:23:55 --> 00:23:58 radial velocity of some 236
00:23:58 --> 00:24:01 km/s. The system also displays an excess
00:24:01 --> 00:24:03 of infrared radiation emissions,
00:24:03 --> 00:24:04 suggesting the presence of a
00:24:04 --> 00:24:07 circumstellar disc of dust. The second
00:24:07 --> 00:24:09 star in the system appears to be inside
00:24:09 --> 00:24:12 this debris disc. Now, astronomers are
00:24:12 --> 00:24:14 speculating that this may well develop
00:24:14 --> 00:24:16 into a spectral type G yellow dwarf star
00:24:16 --> 00:24:20 with about 95% of our sun's mass. Sigma
00:24:20 --> 00:24:21 Sagittarius or Nunki is the
00:24:21 --> 00:24:24 constellation's second brightest star.
00:24:24 --> 00:24:26 We know the name Ni has Babylonian
00:24:26 --> 00:24:28 origins. However, its meaning remains a
00:24:28 --> 00:24:30 mystery. It's thought to represent the
00:24:30 --> 00:24:32 ancient Babylonian city of Erdo on the
00:24:32 --> 00:24:35 Euphrates River. If correct, that would
00:24:35 --> 00:24:37 make NI the oldest known star name
00:24:37 --> 00:24:40 currently in use. It's a spectrotype B
00:24:40 --> 00:24:43 blue star located about 260 lighty years
00:24:43 --> 00:24:45 away. It has about 8 times the sun's
00:24:46 --> 00:24:47 mass, about 4 and a half times its
00:24:47 --> 00:24:50 radius, and some 3 times the
00:24:50 --> 00:24:53 luminosity of our sun. Zeta Sagittaria,
00:24:53 --> 00:24:55 or a cell at the armpit, is a binary
00:24:55 --> 00:24:57 star system 88 lighty years away from
00:24:57 --> 00:24:59 the sun. It's currently speeding away
00:24:59 --> 00:25:01 from the solar system, but may once have
00:25:01 --> 00:25:03 been as near as 1 and a half lightyears
00:25:03 --> 00:25:05 from the sun about 1.4 million years
00:25:05 --> 00:25:07 ago, and that would make it a former
00:25:07 --> 00:25:09 close neighbor. One of the stars in the
00:25:09 --> 00:25:11 system is a spectrotype a white giant,
00:25:12 --> 00:25:13 while the other is a spectrotype a white
00:25:14 --> 00:25:15 super giant. The pair orbiting each
00:25:15 --> 00:25:18 other every 21 Earth years. The systems
00:25:18 --> 00:25:21 combined mass is thought to be 5.26
00:25:21 --> 00:25:24 times the mass of our sun. Delta
00:25:24 --> 00:25:26 Sagittary appears to be a double star
00:25:26 --> 00:25:28 system located around 348 lighty years
00:25:28 --> 00:25:31 away and listed as an orange giant. Then
00:25:31 --> 00:25:33 there's EA Sagittary, another double
00:25:33 --> 00:25:36 star system. This one located 146 lighty
00:25:36 --> 00:25:38 years from Earth. The primary star in
00:25:38 --> 00:25:41 the system is an aging bloated red giant
00:25:41 --> 00:25:43 on the astopic giant branch. That means
00:25:44 --> 00:25:46 it's no longer fusing hydrogen or helium
00:25:46 --> 00:25:47 at its core and is instead fusing
00:25:47 --> 00:25:50 heavier elements, burning hydrogen and
00:25:50 --> 00:25:52 helium in the shell. It's already
00:25:52 --> 00:25:54 expanded out to some 57 times the radius
00:25:54 --> 00:25:57 of our sun and is now nearing the end of
00:25:57 --> 00:25:59 its life. The second star in the system
00:25:59 --> 00:26:01 is a spectrotype F main sequence white
00:26:01 --> 00:26:03 yellow dwarf which appears to be in a
00:26:03 --> 00:26:05 binary system with a primary star
00:26:05 --> 00:26:08 orbiting it every 1 Earth years.
00:26:08 --> 00:26:11 High Sagittary or a Balder is a triple
00:26:11 --> 00:26:13 star system located 510 light years
00:26:13 --> 00:26:16 away. The primary star in the system
00:26:16 --> 00:26:18 appears to be a spectrotype F white
00:26:18 --> 00:26:20 yellow giant which has exhausted its
00:26:20 --> 00:26:22 core hydrogen and so is now off the main
00:26:22 --> 00:26:25 sequence and evolving into a red giant.
00:26:25 --> 00:26:27 We know pi Sagittary has two nearby
00:26:27 --> 00:26:29 companions but little is known about
00:26:29 --> 00:26:32 either of them. Beta Sagittaria or Arab
00:26:32 --> 00:26:34 the Achilles tendon is the designation
00:26:34 --> 00:26:36 shed by two separate star systems. One's
00:26:36 --> 00:26:39 about 378 light years from Earth, the
00:26:39 --> 00:26:41 other 139 light years away. Beta
00:26:42 --> 00:26:44 Sagittary A is a spectrotype B blue
00:26:44 --> 00:26:46 dwarf star while Beta Sagittary B is a
00:26:46 --> 00:26:49 white yellow giant. Lying nearly at the
00:26:49 --> 00:26:50 very center of the constellation
00:26:50 --> 00:26:53 Sagittarius is Nova Sagittary which was
00:26:53 --> 00:26:56 only discovered in 2015 and as its name
00:26:56 --> 00:26:59 suggests is Anova, a white dwarf in a
00:26:59 --> 00:27:01 binary system with another star which is
00:27:01 --> 00:27:02 constantly drawing material off its
00:27:02 --> 00:27:05 companion. Now, once enough material
00:27:05 --> 00:27:07 reaches the surface of the white dwarf,
00:27:07 --> 00:27:09 this added mass triggers a thermonuclear
00:27:09 --> 00:27:11 explosion, causing the star to suddenly
00:27:11 --> 00:27:13 light up like a beacon and then slowly
00:27:13 --> 00:27:15 begin fading again over the following
00:27:15 --> 00:27:18 weeks and months. Now, this blast isn't
00:27:18 --> 00:27:19 strong enough to destroy the white
00:27:19 --> 00:27:21 dwarf, only the additional material that
00:27:21 --> 00:27:23 it's picked up. And with this additional
00:27:23 --> 00:27:25 material now burnt off, the same cycle
00:27:25 --> 00:27:27 can start over again. And the process
00:27:28 --> 00:27:30 can repeat itself on time scales ranging
00:27:30 --> 00:27:31 from every few years to tens of
00:27:31 --> 00:27:33 thousands of years apart.
00:27:34 --> 00:27:36 The Sagittarius constellation also hosts
00:27:36 --> 00:27:39 many star clusters and nebula, including
00:27:39 --> 00:27:40 some of the best known astronomical
00:27:40 --> 00:27:43 objects in the sky. These include the
00:27:43 --> 00:27:46 Lagoon Nebula, Messier 8, a spectacular
00:27:46 --> 00:27:48 pink emission nebula located 8
00:27:48 --> 00:27:50 lighty years away, which measures 140
00:27:50 --> 00:27:53 lighty years by 60 light years across.
00:27:53 --> 00:27:55 The central area of the Lagoon Nebula is
00:27:55 --> 00:27:57 also known as the Hourglass Nebula
00:27:57 --> 00:27:59 because of its distinctive shape. The
00:27:59 --> 00:28:01 shapes caused by matter propelled by a
00:28:01 --> 00:28:03 massive star forming in a region known
00:28:03 --> 00:28:05 as Hershel 36, one of the few star
00:28:05 --> 00:28:07 forming nebula that's possible to see
00:28:07 --> 00:28:09 with the unaded eye. The Lagoon Nebula
00:28:09 --> 00:28:11 was instrumental in the discovery of
00:28:11 --> 00:28:13 what are known as Boach globules, more
00:28:13 --> 00:28:15 than 17 of which have now been found
00:28:15 --> 00:28:18 in the nebula. Astronomers believe Bach
00:28:18 --> 00:28:21 globules contain embriionic protoars
00:28:21 --> 00:28:22 destined to eventually become new
00:28:22 --> 00:28:25 stellar generations.
00:28:25 --> 00:28:26 Probably the best known nebula in
00:28:26 --> 00:28:29 Sagittarius is Messier 17, the Horsehead
00:28:29 --> 00:28:33 Nebula. It's located 4 lighty years
00:28:33 --> 00:28:35 away and is a dense region of ionized
00:28:35 --> 00:28:39 atomic hydrogen. Also known as the Omega
00:28:39 --> 00:28:41 or Swan Nebula, it spans some 15 lighty
00:28:41 --> 00:28:43 years in diameter and has some 800 times
00:28:43 --> 00:28:46 the mass of our sun. It's considered one
00:28:46 --> 00:28:48 of the brightest and most massive star
00:28:48 --> 00:28:50 forming regions in our galaxy with a
00:28:50 --> 00:28:51 geometry very similar to the Orion
00:28:52 --> 00:28:54 Nebula except that it's viewed air on
00:28:54 --> 00:28:56 rather than face on. The open star
00:28:56 --> 00:28:57 cluster
00:28:57 --> 00:29:00 NGC618 is embedded within the nebulosity
00:29:00 --> 00:29:02 and it causes the gases of the nebula to
00:29:02 --> 00:29:04 shine due to intense radiation from
00:29:04 --> 00:29:07 these hot young stars. Open star
00:29:07 --> 00:29:09 clusters are loosely bound groups of a
00:29:09 --> 00:29:11 few thousand stars which were originally
00:29:11 --> 00:29:13 all formed in the same molecular gas and
00:29:13 --> 00:29:15 dust cloud but are not as tightly bonded
00:29:15 --> 00:29:17 together as the stars in globular
00:29:17 --> 00:29:19 clusters. It's thought open clusters
00:29:19 --> 00:29:21 generally survive for a few hundred
00:29:21 --> 00:29:23 million years with the most massive ones
00:29:23 --> 00:29:25 surviving for maybe a few billion years.
00:29:26 --> 00:29:27 In contrast, the more massive globular
00:29:27 --> 00:29:29 clusters exert far stronger
00:29:29 --> 00:29:31 gravitational attraction to their
00:29:31 --> 00:29:33 members and they therefore can survive
00:29:33 --> 00:29:36 much longer in cosmic time. The nebula
00:29:36 --> 00:29:38 is thought to contain over 800 stars,
00:29:38 --> 00:29:39 including more than a hundred of the
00:29:39 --> 00:29:42 largest, most massive spectrotype OMB
00:29:42 --> 00:29:44 blue stars. More than a thousand
00:29:44 --> 00:29:47 additional stars are now being formed in
00:29:47 --> 00:29:49 the surrounding molecular gas and dust
00:29:49 --> 00:29:51 clouds. It's also one of the youngest
00:29:51 --> 00:29:53 known clusters in the galaxy with an age
00:29:53 --> 00:29:55 of just a million years. The cloud of
00:29:55 --> 00:29:57 interstellar material forming the nebula
00:29:57 --> 00:29:59 is roughly 40 light years in diameter
00:29:59 --> 00:30:01 and it's thought to contain some 30
00:30:02 --> 00:30:03 solar masses.
00:30:03 --> 00:30:05 Another famous nebulosity is the
00:30:05 --> 00:30:09 Trifford Nebula Messia 20. It's another
00:30:09 --> 00:30:10 large star forming emission nebula
00:30:10 --> 00:30:13 containing many very young hot stars
00:30:14 --> 00:30:15 located somewhere between 2 and
00:30:15 --> 00:30:17 9 lighty years from Earth. The
00:30:17 --> 00:30:19 Triffford Nebula has a diameter of
00:30:19 --> 00:30:21 around 50 lighty years. Now, the outside
00:30:21 --> 00:30:23 of the Trefford Nebula is a bluish
00:30:23 --> 00:30:25 reflection nebula, while the inner
00:30:25 --> 00:30:27 region is glowing pink thanks to ionized
00:30:27 --> 00:30:29 hydrogen. There are two dark bands
00:30:29 --> 00:30:31 dividing the Triffford Nebula into three
00:30:31 --> 00:30:34 regions or loes. Hydrogen in the nebula
00:30:34 --> 00:30:36 is being ionized by a central triple
00:30:36 --> 00:30:38 star system which formed in the
00:30:38 --> 00:30:40 intersection of the two bands creating
00:30:40 --> 00:30:43 the characteristic pink color. Other
00:30:43 --> 00:30:46 star forming regions such as
00:30:46 --> 00:30:48 NGC559 which is located 5 lighty
00:30:48 --> 00:30:50 years from Earth contain both red
00:30:50 --> 00:30:53 emission and blue reflection regions.
00:30:53 --> 00:30:55 This grouping of the Lagoon Nebula, the
00:30:55 --> 00:30:57 Triffid Nebula, and
00:30:57 --> 00:31:00 NGC6559 is known as the Sagittarius
00:31:00 --> 00:31:03 triplet. Another spectacular site in
00:31:03 --> 00:31:07 Sagittarius is the Red Spider Nebula,
00:31:07 --> 00:31:09 NGC6537. It's a planetary nebula some
00:31:09 --> 00:31:12 8 lighty years from Earth. It is a
00:31:12 --> 00:31:14 prominent two-lo shape. Now, this could
00:31:14 --> 00:31:16 be due to a binary companion or possibly
00:31:16 --> 00:31:18 magnetic fields and has an S-shaped
00:31:18 --> 00:31:20 symmetry with the loes opposite each
00:31:20 --> 00:31:22 other appearing similar. The central
00:31:22 --> 00:31:25 white dwarf remnant to the original star
00:31:25 --> 00:31:27 produces a powerful 10 degree hot
00:31:27 --> 00:31:31 3 km/s stellar wind. And that wind
00:31:31 --> 00:31:33 is generating 100 billion km high waves
00:31:34 --> 00:31:36 of supersonic shocks which are formed as
00:31:36 --> 00:31:38 local gas is being compressed and heated
00:31:38 --> 00:31:41 in front of the rapidly expanding loes.
00:31:41 --> 00:31:43 Atoms caught in the shock front are
00:31:43 --> 00:31:44 radiating invisible light, giving the
00:31:44 --> 00:31:47 nebula its unique spiderlike shape and
00:31:47 --> 00:31:49 also contributing to its expansion. The
00:31:49 --> 00:31:51 star at the center of the Red Spartan
00:31:51 --> 00:31:53 Nebula is shrouded by a dust chill,
00:31:53 --> 00:31:55 making its exact properties hard to
00:31:55 --> 00:31:57 determine. We think it has a surface
00:31:57 --> 00:31:58 temperature of around
00:31:58 --> 00:32:00 25°, although temperatures of up to
00:32:00 --> 00:32:02 half a million degrees can't be ruled
00:32:02 --> 00:32:04 out, which would make it one of the
00:32:04 --> 00:32:06 hottest white dwarf stars known.
00:32:06 --> 00:32:08 Now, if you look directly south this
00:32:08 --> 00:32:10 time of year, you'll find the star
00:32:10 --> 00:32:12 Polaris Astralis, or more accurately,
00:32:12 --> 00:32:15 Sigma Octanis, the nearest star to the
00:32:15 --> 00:32:16 southern celestial pole, and
00:32:16 --> 00:32:18 consequently the counterpart to the
00:32:18 --> 00:32:21 north star Polaris. However, Sigma
00:32:21 --> 00:32:22 Octanis is much harder to see than
00:32:22 --> 00:32:25 Polaris because it's much fainter.
00:32:25 --> 00:32:27 Located some 270 light years away, it's
00:32:27 --> 00:32:29 now an orange giant nearing the end of
00:32:29 --> 00:32:32 its life. Turning to the southwest just
00:32:32 --> 00:32:35 above the horizon and we find Kenopus,
00:32:35 --> 00:32:37 second brightest star in the night sky
00:32:37 --> 00:32:40 after Sirius. It's located some 310
00:32:40 --> 00:32:42 lighty years away and is the brightest
00:32:42 --> 00:32:43 star in the constellation Korean of the
00:32:43 --> 00:32:47 ke. Kenopus is a super giant some 9
00:32:47 --> 00:32:49 times the mass of the sun and some 71
00:32:49 --> 00:32:50 times its
00:32:50 --> 00:32:53 diameter. The month of June also marks
00:32:53 --> 00:32:55 the first of two annual encounters with
00:32:55 --> 00:32:58 a torids meteor shower. The torids are
00:32:58 --> 00:33:00 generated as the Earth passes through a
00:33:00 --> 00:33:02 debris stream left by the comet 2P Anki,
00:33:02 --> 00:33:04 which itself could be pieces of a much
00:33:04 --> 00:33:06 larger comet that broke apart around
00:33:06 --> 00:33:09 20 to 30 years ago, most likely
00:33:09 --> 00:33:10 following numerous interactions with the
00:33:10 --> 00:33:12 powerful gravitational field of the
00:33:12 --> 00:33:15 planet Jupiter. As their name suggests,
00:33:15 --> 00:33:17 the Torid's radiant or apparent point of
00:33:17 --> 00:33:19 origin is in the constellation Taurus,
00:33:19 --> 00:33:22 the bull. The Torid meteor shell is made
00:33:22 --> 00:33:24 up of larger and more massive material.
00:33:24 --> 00:33:26 Think of pebbles instead of dust grains.
00:33:26 --> 00:33:28 Earth passes through this stream twice
00:33:28 --> 00:33:30 every year. Once in June, then again in
00:33:30 --> 00:33:32 October when they're referred to as
00:33:32 --> 00:33:35 Halloween fireballs. The torids release
00:33:35 --> 00:33:37 material both by normal cometry activity
00:33:37 --> 00:33:39 and occasionally through close
00:33:39 --> 00:33:40 encounters with the gravitational tidal
00:33:40 --> 00:33:42 forces exerted by the Earth and other
00:33:42 --> 00:33:45 planets. And all this makes the torid
00:33:45 --> 00:33:47 stream of material the largest in the
00:33:47 --> 00:33:49 inner solar system. Now, since this
00:33:49 --> 00:33:51 meteor stream is rather spread out in
00:33:51 --> 00:33:53 space, planet Earth takes several weeks
00:33:53 --> 00:33:55 to pass through it, causing an extended
00:33:55 --> 00:33:57 period of meteor activity compared with
00:33:57 --> 00:33:59 a much smaller periods of activity by
00:33:59 --> 00:34:01 other meteor showers. Now, included in
00:34:01 --> 00:34:03 the Toret stream is a denser flow of
00:34:03 --> 00:34:05 grally meteors called the Torid Swarm.
00:34:06 --> 00:34:07 And they're thought to be a ribbon of
00:34:07 --> 00:34:10 rocks roughly 75 million km by 150 km
00:34:10 --> 00:34:12 across and held in orbit by Jupiter's
00:34:12 --> 00:34:14 gravity.
00:34:14 --> 00:34:16 Now, occasionally, planet Earth passes
00:34:16 --> 00:34:18 through the larger meteors in this
00:34:18 --> 00:34:20 denser torid swarm. And one of the
00:34:20 --> 00:34:22 larger chunks in the torid swarm is now
00:34:22 --> 00:34:24 thought to have caused the infamous
00:34:24 --> 00:34:26 Tonguska event in the skies above
00:34:26 --> 00:34:29 Siberia on June the 30th, 1908. The
00:34:29 --> 00:34:31 Tangaska event is now believed to have
00:34:31 --> 00:34:33 been the air burst of a 100 meter wide
00:34:33 --> 00:34:36 meteor in the skies above the Tangaska
00:34:36 --> 00:34:38 region of Russia, resulting in mass
00:34:38 --> 00:34:40 devastation over a 2 square
00:34:40 --> 00:34:42 kilometer region of forest, turning
00:34:42 --> 00:34:45 trees in matchixs. In fact, the blast
00:34:45 --> 00:34:47 was so bright it lit up the night sky in
00:34:47 --> 00:34:49 London a third of the way around the
00:34:49 --> 00:34:51 planet. The Tanguska event remains the
00:34:52 --> 00:34:54 largest known Earth impact event of a
00:34:54 --> 00:34:57 meteor in recorded modern times. Now,
00:34:57 --> 00:34:58 it's always been considered to be a one
00:34:58 --> 00:35:00 in a thousand-year event, assuming a
00:35:00 --> 00:35:03 random distribution of events over time.
00:35:03 --> 00:35:04 But there's a problem with that because
00:35:04 --> 00:35:06 of these new studies suggesting the
00:35:06 --> 00:35:07 event may have been caused by a torid
00:35:07 --> 00:35:09 swarm meteor. And with the Earth passing
00:35:09 --> 00:35:11 through the torret swarm periodically,
00:35:11 --> 00:35:14 it changes the odds considerably. Now,
00:35:14 --> 00:35:16 if this new stud is correct, the swarm
00:35:16 --> 00:35:17 heightens the possibility of a cluster
00:35:17 --> 00:35:19 of large impacts on Earth over a short
00:35:19 --> 00:35:21 period of time. Now, further
00:35:21 --> 00:35:23 complicating matters, the June torids
00:35:23 --> 00:35:26 are actually two separate showers. The
00:35:26 --> 00:35:28 southern torids are associated with a
00:35:28 --> 00:35:30 comet 2P Anki, while the northern Torids
00:35:30 --> 00:35:33 originate from the asteroid 2004 TG10,
00:35:34 --> 00:35:35 an eccentric kilometer wide asteroid
00:35:36 --> 00:35:38 classified as a near-Earth object and a
00:35:38 --> 00:35:39 potentially hazardous asteroid of the
00:35:39 --> 00:35:43 Apollo group. Something to think about.
00:35:43 --> 00:35:44 Joining us now for the rest of our tour
00:35:44 --> 00:35:46 of the night skies of June is science
00:35:46 --> 00:35:48 editor Jonathan Nally. Good day, Stu.
00:35:48 --> 00:35:50 Yeah, well, it's June. So, June evenings
00:35:50 --> 00:35:53 start off with the constellation Orion
00:35:53 --> 00:35:55 low in the west. So Orion's one of our
00:35:55 --> 00:35:56 favorite constellations, isn't it? I
00:35:56 --> 00:35:58 love Orion. Everyone loves Orion. That's
00:35:58 --> 00:36:00 very easily recognizable. But it is low
00:36:00 --> 00:36:03 in the west after sunset. And as the
00:36:03 --> 00:36:05 Earth turns during the evening, it dips
00:36:05 --> 00:36:07 below the horizon pretty quickly. And by
00:36:07 --> 00:36:08 the middle of the month, it's actually
00:36:08 --> 00:36:09 going to be gone. After sunset, you
00:36:09 --> 00:36:11 won't be able to see it anymore. But it
00:36:11 --> 00:36:13 will reappear towards the end of the
00:36:13 --> 00:36:14 year in the eastern sky. And that's when
00:36:14 --> 00:36:16 Orion appears in the eastern sky at the
00:36:16 --> 00:36:17 end of the year. That's when you know
00:36:17 --> 00:36:18 that for people in the southern
00:36:18 --> 00:36:20 hemisphere, summer is arriving. Or for
00:36:20 --> 00:36:21 people in the northern hemisphere, they
00:36:21 --> 00:36:23 know that winter is arriving. So it's
00:36:23 --> 00:36:25 it's a good sign postpion but yeah you
00:36:25 --> 00:36:26 get your last glimpse of it now
00:36:26 --> 00:36:28 basically in the evening the first half
00:36:28 --> 00:36:30 of June also in the western part of the
00:36:30 --> 00:36:32 sky there are two bright stars one's
00:36:32 --> 00:36:34 called Sirius the other one's called
00:36:34 --> 00:36:36 Prosion Sirius is the brightest star in
00:36:36 --> 00:36:39 the night sky is the eighth brightest
00:36:39 --> 00:36:41 still very bright and they have a few
00:36:41 --> 00:36:42 similarities actually they're both
00:36:42 --> 00:36:45 binary stars and each of them is a what
00:36:45 --> 00:36:47 they call a main sequence a normal sort
00:36:47 --> 00:36:48 of star with a white dwarf going around
00:36:48 --> 00:36:50 it a white dwarf star and they're both
00:36:50 --> 00:36:52 within constellations that have the word
00:36:52 --> 00:36:54 dog In the name Sirius is in the
00:36:54 --> 00:36:56 constellation Panis Major or the greater
00:36:56 --> 00:36:59 dog and Croan is in the constellation
00:36:59 --> 00:37:01 Panis minor or the lesser dog. In the
00:37:01 --> 00:37:03 southwest there's another bright star
00:37:03 --> 00:37:05 Canopus. Canopus is my favorite star in
00:37:05 --> 00:37:06 the whole sky. I reckon it's the second
00:37:06 --> 00:37:08 brightest star in the night sky. About
00:37:08 --> 00:37:10 half as bright as Sirius. You only get a
00:37:10 --> 00:37:11 really good look of it look at it if
00:37:11 --> 00:37:13 you're in the southern hemisphere. From
00:37:13 --> 00:37:15 people in the northern hemisphere to the
00:37:15 --> 00:37:17 lower latitude you can see it uh certain
00:37:17 --> 00:37:19 times of the year but um from down here
00:37:19 --> 00:37:20 it's pretty much visible all the time.
00:37:20 --> 00:37:22 It's actually the most luminous star in
00:37:22 --> 00:37:24 our neighborhood. It's huge. Yeah, it
00:37:24 --> 00:37:26 is. It's about 10 times brighter
00:37:26 --> 00:37:28 than our sun, about 10 times its size.
00:37:28 --> 00:37:30 And fortunately, it is about 310 light
00:37:30 --> 00:37:32 years away, which is very close in space
00:37:32 --> 00:37:34 terms, but if it was much closer than
00:37:34 --> 00:37:37 310 light years away, it would be very,
00:37:37 --> 00:37:39 very bright indeed. I mean, you I mean,
00:37:39 --> 00:37:41 if it was, you know, a fraction of that
00:37:41 --> 00:37:42 distance, you really wouldn't have a
00:37:42 --> 00:37:44 night sky. Is it the case that Kenopus
00:37:44 --> 00:37:47 was once closer to our star system than
00:37:47 --> 00:37:49 Sirius and then it moved away and it
00:37:49 --> 00:37:50 it's slowly coming back again? I think
00:37:50 --> 00:37:52 it is the case. Yeah, I think it is the
00:37:52 --> 00:37:54 case that um the the distances have
00:37:54 --> 00:37:56 changed a little bit and Kenopus at one
00:37:56 --> 00:37:58 point was brighter than Sirius I think.
00:37:58 --> 00:38:01 So you we're moving our souls moving
00:38:01 --> 00:38:02 through space and Sirius is moving
00:38:02 --> 00:38:03 through space and Kenopus is moving
00:38:03 --> 00:38:05 through space. So the distances between
00:38:05 --> 00:38:08 each other are moving around a bit but
00:38:08 --> 00:38:09 yeah Kenopus at the moment is not as
00:38:09 --> 00:38:11 bright as Siri. series is is the is the
00:38:11 --> 00:38:13 brightest star. But, you know, you go
00:38:13 --> 00:38:15 out to the to the naked eye, telling one
00:38:15 --> 00:38:18 star apart of that brightness, telling
00:38:18 --> 00:38:21 one star apart from another is um it's
00:38:21 --> 00:38:23 not the easiest thing to do. If you get
00:38:23 --> 00:38:24 a good look at both and you say, "Yeah,
00:38:24 --> 00:38:26 yeah, well, series is brighter." But,
00:38:26 --> 00:38:27 you know, they both are very very
00:38:27 --> 00:38:28 bright. But yeah, I don't know. Canopus
00:38:28 --> 00:38:29 is just one of my favorites really. I
00:38:30 --> 00:38:30 guess because it was one of the first
00:38:30 --> 00:38:32 stars I identified when I was a kid and
00:38:32 --> 00:38:34 because it's nice bright star, far down
00:38:34 --> 00:38:35 the southern style, we sort of got it
00:38:35 --> 00:38:37 all to our sh sort of thing. So it's
00:38:37 --> 00:38:39 it's uh just got a sort of a sentimental
00:38:39 --> 00:38:41 value for me. We're very lucky in the
00:38:41 --> 00:38:43 southern hemisphere, aren't we? Oh,
00:38:43 --> 00:38:43 we're super lucky in the southern
00:38:44 --> 00:38:45 hemisphere. We got lots of bright
00:38:45 --> 00:38:46 things. We got the uh center of the
00:38:46 --> 00:38:48 Milky Way galaxy overhead and we got the
00:38:48 --> 00:38:50 Magelani cloud galaxies. There are
00:38:50 --> 00:38:51 plenty of good things, which is not to
00:38:51 --> 00:38:52 say that there aren't plenty of great
00:38:52 --> 00:38:54 things in the northern sky as well, but
00:38:54 --> 00:38:57 we um we do have a few extras of down
00:38:57 --> 00:38:59 here that makes it a bit special. Now
00:38:59 --> 00:39:00 high in the south about twothirds of the
00:39:00 --> 00:39:02 way up from the horizon down in the
00:39:02 --> 00:39:03 south you got the southern cross this
00:39:03 --> 00:39:05 time of year and it's standing upright
00:39:05 --> 00:39:07 for a change because a lot of the year
00:39:07 --> 00:39:09 it's either upside down or on its left
00:39:09 --> 00:39:10 side or on the right side or whatever
00:39:10 --> 00:39:12 but round about now it's pretty much
00:39:12 --> 00:39:15 standing upright nearby you got the pair
00:39:15 --> 00:39:17 of stars known as the two pointers alpha
00:39:17 --> 00:39:19 and beta centur we talk about those a
00:39:19 --> 00:39:21 lot on the show the Milky Way runs right
00:39:21 --> 00:39:23 through this region of the cross it's
00:39:23 --> 00:39:24 sort of heading from east to west across
00:39:24 --> 00:39:26 the sky and there are plenty of star
00:39:26 --> 00:39:27 clusters and nebula for amateur
00:39:27 --> 00:39:29 astronomers to enjoy looking along its
00:39:29 --> 00:39:31 length. Even with a pair of binoculars,
00:39:31 --> 00:39:32 with a telescope, it's great,
00:39:32 --> 00:39:33 particularly if you've got one that
00:39:33 --> 00:39:35 gives you a wide field of view, but just
00:39:35 --> 00:39:36 binoculars looks really superb along
00:39:36 --> 00:39:38 there. You do need dark skies, though.
00:39:38 --> 00:39:41 The city skies make it do make it very,
00:39:41 --> 00:39:42 very hard with all the light pollution.
00:39:42 --> 00:39:44 Now, if you do have really dark skies
00:39:44 --> 00:39:45 and you've got a clear southern horizon,
00:39:46 --> 00:39:47 you might be able to see two smudges of
00:39:48 --> 00:39:49 light above the southern horizon. And
00:39:49 --> 00:39:50 those are these melanic clouds I was
00:39:50 --> 00:39:52 talking about earlier. These are small
00:39:52 --> 00:39:54 oddshaped galaxies that are very close
00:39:54 --> 00:39:56 to the Milky Way. They're they're the
00:39:56 --> 00:39:58 nearest sizable galaxies to our own and
00:39:58 --> 00:39:59 you can see them just with the naked
00:39:59 --> 00:40:01 eye. If you've got dark skies and you
00:40:01 --> 00:40:03 let your eyes get back into the dark,
00:40:03 --> 00:40:04 they just look like clouds. They look
00:40:04 --> 00:40:07 like tiny clouds, hence their name
00:40:07 --> 00:40:09 clouds. There's actually a bit of a push
00:40:09 --> 00:40:12 on to rename them, do away with the name
00:40:12 --> 00:40:14 Mellan because, you know, in keeping
00:40:14 --> 00:40:15 with the way kings are these days, you
00:40:15 --> 00:40:17 know, Mr. Mellin, or at least the voyage
00:40:17 --> 00:40:19 that he was on, was not too kind to some
00:40:19 --> 00:40:21 of the people and places that they
00:40:21 --> 00:40:23 visited on their around the world trip.
00:40:23 --> 00:40:25 So um in the spirit of that some people
00:40:25 --> 00:40:27 are trying to have that those clouds
00:40:27 --> 00:40:29 renamed small and large milky clouds or
00:40:29 --> 00:40:30 something along that line sort of
00:40:30 --> 00:40:32 similar to the Milky Way. So we'll see
00:40:32 --> 00:40:34 how far that gets in the northern half
00:40:34 --> 00:40:35 of the sky as seen from the southern
00:40:35 --> 00:40:37 hemisphere at least. It does seem a bit
00:40:37 --> 00:40:38 bare this time of year but there is the
00:40:38 --> 00:40:40 bright star Arcturus which you can see
00:40:40 --> 00:40:42 about halfway up from the northern
00:40:42 --> 00:40:43 horizon. You've got another bright star
00:40:44 --> 00:40:45 that's reasonably overhead from the
00:40:45 --> 00:40:47 latitude of Sydney. That star is called
00:40:47 --> 00:40:49 Spiker. And as the night goes on though,
00:40:49 --> 00:40:51 you'll see that things have to change
00:40:51 --> 00:40:53 because the earth is rotating. By
00:40:53 --> 00:40:55 midnight, Sirius has already set in the
00:40:55 --> 00:40:57 west. The brightest star has already set
00:40:57 --> 00:40:58 in the west. And a couple of other
00:40:58 --> 00:40:59 bright stars have appeared in the north.
00:40:59 --> 00:41:02 You got Vega and Altter, which are very
00:41:02 --> 00:41:03 famous stars. They appear in lots of
00:41:03 --> 00:41:06 science fiction and and TV series, those
00:41:06 --> 00:41:07 sort of things. And there's another star
00:41:07 --> 00:41:09 in the southeast actually another one
00:41:09 --> 00:41:11 like very far in the southeast down the
00:41:11 --> 00:41:12 southern sky. It's one of these ones
00:41:12 --> 00:41:13 that you can see really only from the
00:41:13 --> 00:41:15 southern hemisphere. It's called Akonar.
00:41:15 --> 00:41:17 And that's actually one of another one
00:41:17 --> 00:41:18 of my favorite stars. Again, probably
00:41:18 --> 00:41:20 just got it sort of special because it's
00:41:20 --> 00:41:22 only visible from the south. And the
00:41:22 --> 00:41:23 Milky Way, which was stretching, as I
00:41:23 --> 00:41:25 said, was stretching east to west sort
00:41:25 --> 00:41:27 of horizontally across the sky. It's now
00:41:27 --> 00:41:28 stretching from the northeast to the
00:41:28 --> 00:41:30 southwest sort of diagonally across the
00:41:30 --> 00:41:31 sky. That's just because the Earth is
00:41:31 --> 00:41:32 turning and we get a different
00:41:32 --> 00:41:34 perspective. Now, turning to the
00:41:34 --> 00:41:36 planets. What have we got? Well, we got
00:41:36 --> 00:41:38 Jupiter at the moment is out of view.
00:41:38 --> 00:41:40 It's too close to the sun to be seen.
00:41:40 --> 00:41:41 That'll be that way for a little while.
00:41:41 --> 00:41:43 The same goes for Mercury, actually.
00:41:43 --> 00:41:45 Although, if you are lucky, and by lucky
00:41:45 --> 00:41:46 I mean if you've got a good clear
00:41:46 --> 00:41:48 horizon and there's no buildings and
00:41:48 --> 00:41:49 trees and things in the way, you might
00:41:49 --> 00:41:51 just be able to spot Mercury very low
00:41:51 --> 00:41:53 above the western horizon after the sun
00:41:53 --> 00:41:56 has set in the last week or so of June.
00:41:56 --> 00:41:58 Other than that, it's um it's very very
00:41:58 --> 00:42:00 close to the sun and very hard to see.
00:42:00 --> 00:42:02 Around mid evening time, after it gets
00:42:02 --> 00:42:05 dark, Mars can be seen about halfway up
00:42:05 --> 00:42:06 from the horizon very easily. It's a
00:42:06 --> 00:42:09 sort of a looks like a red star or or an
00:42:09 --> 00:42:12 orangey reddish kind of star as I say
00:42:12 --> 00:42:14 about halfway up from the horizon to the
00:42:14 --> 00:42:15 north if you're viewing from the
00:42:15 --> 00:42:17 southern hemisphere or to the south if
00:42:17 --> 00:42:18 you're viewing from the northern
00:42:18 --> 00:42:20 hemisphere. So see if you can spot that
00:42:20 --> 00:42:22 one. If you want to spot Saturn, you
00:42:22 --> 00:42:23 have to stay up a bit later. It rises
00:42:23 --> 00:42:25 above the eastern horizon about 1:30
00:42:25 --> 00:42:27 a.m. at the beginning of month and by
00:42:27 --> 00:42:30 about midnight at the end of June, which
00:42:30 --> 00:42:31 is a bit past my usual daytime these
00:42:32 --> 00:42:33 days, but if you're out and about late,
00:42:33 --> 00:42:34 you should be able to spot it quite
00:42:34 --> 00:42:36 easily. It's fairly bright. Has a
00:42:36 --> 00:42:38 slightly yellowish tinge. So, be coming
00:42:38 --> 00:42:40 up over the horizon about 1:30 a.m. at
00:42:40 --> 00:42:41 the beginning of the month. And finally,
00:42:41 --> 00:42:43 we've got Venus, which will also be
00:42:43 --> 00:42:44 rising over the horizon. It follows
00:42:44 --> 00:42:47 Saturn, but at around about 3:45 a.m.
00:42:47 --> 00:42:49 So, you have to stay up very, very late
00:42:49 --> 00:42:51 for that one. Um, night owls will be
00:42:51 --> 00:42:53 able to get a view of that, which you
00:42:53 --> 00:42:54 can't miss Venus doors. I always say
00:42:54 --> 00:42:56 this, it's so big and bright, you just
00:42:56 --> 00:42:57 can't miss it. It's the third brightest
00:42:57 --> 00:42:59 thing in the sky after the sun and the
00:42:59 --> 00:43:00 moon. So, night time, of course, very
00:43:00 --> 00:43:03 easy to just spot Venus. You were just
00:43:03 --> 00:43:04 coming home from the club at that time,
00:43:04 --> 00:43:05 weren't you? Coming home from the club
00:43:05 --> 00:43:07 in my dreams, I think. No, I think um
00:43:07 --> 00:43:10 night owls, those who night shifts and
00:43:10 --> 00:43:11 those people getting up early for
00:43:11 --> 00:43:13 morning shifts will be able to spot it.
00:43:13 --> 00:43:14 It's one of these things actually where
00:43:14 --> 00:43:16 there are a lot of UFO reports when
00:43:16 --> 00:43:17 people, you know, say get up early in
00:43:17 --> 00:43:18 the morning. They're not accustomed to
00:43:18 --> 00:43:19 being up early in the morning and they
00:43:20 --> 00:43:22 look out bright white light doesn't seem
00:43:22 --> 00:43:23 to be moving and they think, "Oh, it's a
00:43:23 --> 00:43:25 UFO where, you know, it wasn't there
00:43:25 --> 00:43:27 yesterday." Reality is that it was there
00:43:27 --> 00:43:28 yesterday. You just didn't notice it.
00:43:28 --> 00:43:29 And that's Venus. Sometimes Venus is
00:43:30 --> 00:43:31 visible in the morning's sky and
00:43:31 --> 00:43:33 sometimes Venus is visible in the
00:43:33 --> 00:43:34 evening sky and the same goes for
00:43:34 --> 00:43:36 Mercury. So it does tend to move around
00:43:36 --> 00:43:38 a little bit, but um there's nothing
00:43:38 --> 00:43:39 like the view of Venus. And if you get
00:43:39 --> 00:43:41 out, as we say, sorry, if you go bush,
00:43:42 --> 00:43:43 uh you know, get away from the cities,
00:43:43 --> 00:43:44 get away from the city lights and
00:43:44 --> 00:43:46 everything. So you get really dark
00:43:46 --> 00:43:48 skies, you know, when Venus is big and
00:43:48 --> 00:43:50 bright and up like that, you know, throw
00:43:50 --> 00:43:51 shadows. It's bright enough to throw
00:43:51 --> 00:43:53 shadows. You can see where you're going
00:43:53 --> 00:43:55 just by the light of Venus alone. It's
00:43:55 --> 00:43:56 uh it's really quite remarkable.
00:43:56 --> 00:43:57 Interesting thing about Venus. Found
00:43:57 --> 00:44:00 this from a old Isaac Azimov book. Now,
00:44:00 --> 00:44:01 I don't know whether he was the first
00:44:01 --> 00:44:03 one to come up with this idea or not,
00:44:03 --> 00:44:05 but um I I read it. Yeah, an old cuz he
00:44:05 --> 00:44:08 used to write science essays and science
00:44:08 --> 00:44:09 columns and science books and things as
00:44:09 --> 00:44:11 well as his science fiction and he he
00:44:12 --> 00:44:13 said that you know because we've got the
00:44:13 --> 00:44:15 moon going around the earth right which
00:44:15 --> 00:44:17 is a fairly big moon compared to the
00:44:17 --> 00:44:19 size of the earth moons it's a quarter
00:44:19 --> 00:44:21 of the size of the earth it's huge yeah
00:44:21 --> 00:44:22 some people might call it a double
00:44:22 --> 00:44:24 planet system in a way it's a very large
00:44:24 --> 00:44:26 moon was just a little bit closer the
00:44:26 --> 00:44:29 barry center would be outside the earth
00:44:29 --> 00:44:31 and under those circumstances then we
00:44:31 --> 00:44:33 would be a binary system like Pluto and
00:44:33 --> 00:44:34 Sharon that's exactly You're right. Now
00:44:34 --> 00:44:36 that now what he proposed in this
00:44:36 --> 00:44:38 article was and this could have changed
00:44:38 --> 00:44:39 the cause of history actually if this
00:44:39 --> 00:44:41 had happened was that if the moon hadn't
00:44:42 --> 00:44:44 formed around Earth if instead it had
00:44:44 --> 00:44:47 formed in orbit around Venus and Venus
00:44:47 --> 00:44:49 is about the same size as the Earth then
00:44:49 --> 00:44:51 at the distance of Venus when the moon
00:44:52 --> 00:44:54 was at its furthest from Venus you would
00:44:54 --> 00:44:56 be able to see just with the unaded eye
00:44:56 --> 00:44:58 you would be able to see Venus and its
00:44:58 --> 00:45:00 moon theoretical moon or hypothetical
00:45:00 --> 00:45:02 moon separated on the night sky and you
00:45:02 --> 00:45:04 would see that moon's position changing
00:45:04 --> 00:45:05 from night to night and you would be
00:45:05 --> 00:45:07 drawn to the inescapable conclusion that
00:45:07 --> 00:45:10 that small dot was circling the larger
00:45:10 --> 00:45:12 dot, right? So something was going
00:45:12 --> 00:45:14 around something else and of course we
00:45:14 --> 00:45:15 remember from our history about things,
00:45:15 --> 00:45:17 you know, were thing things going around
00:45:17 --> 00:45:18 the earth or was the earth going around
00:45:18 --> 00:45:20 the sun. So the sun going around the
00:45:20 --> 00:45:21 earth, earth going around the sun and
00:45:21 --> 00:45:23 for a long time of course it was
00:45:23 --> 00:45:26 people and before him. Yeah. Yeah. Well,
00:45:26 --> 00:45:28 see the you know it took until Galileo
00:45:28 --> 00:45:30 looking through his telescope to see
00:45:30 --> 00:45:31 that the moons were going around
00:45:31 --> 00:45:33 Jupiter. or something else, you know,
00:45:33 --> 00:45:34 and yet it moves and something's going
00:45:34 --> 00:45:37 around Jupiter. Well, if if the moon had
00:45:37 --> 00:45:39 formed the orbit around Venus, then we
00:45:39 --> 00:45:41 we would have known since antiquity, you
00:45:41 --> 00:45:43 know, since since, you know, prehistoric
00:45:43 --> 00:45:44 times that something was going around
00:45:44 --> 00:45:46 something else out there in space. And
00:45:46 --> 00:45:48 therefore, we would have known that not
00:45:48 --> 00:45:50 everything goes around the earth. In
00:45:50 --> 00:45:52 other words, this whole idea that the
00:45:52 --> 00:45:53 earth being the center of everything,
00:45:53 --> 00:45:55 which sort of held us back for a very
00:45:55 --> 00:45:57 long time, uh might not have taken hold
00:45:57 --> 00:46:00 or at least um not as widely taken hold
00:46:00 --> 00:46:02 or for as long. So just one of those
00:46:02 --> 00:46:04 accidents of nature that the the moon
00:46:04 --> 00:46:06 formed in orbit around the earth rather
00:46:06 --> 00:46:08 than Venus. Interesting, isn't it? For a
00:46:08 --> 00:46:10 long time, people used to think that
00:46:10 --> 00:46:12 because Venus is covered in clouds and
00:46:12 --> 00:46:13 it's a bit closer to the sun than the
00:46:13 --> 00:46:15 Earth. Then those clouds must mean lots
00:46:16 --> 00:46:17 of rain. Lots of rain means lots of
00:46:18 --> 00:46:19 water on the ground. Lots of water on
00:46:19 --> 00:46:21 the ground means lots of trees could
00:46:21 --> 00:46:23 have grown. Lots of forests. Probably
00:46:23 --> 00:46:24 tropical rainforest would have grown
00:46:24 --> 00:46:26 there. Yeah, because Venus is close to
00:46:26 --> 00:46:27 the sun. Therefore, it would have been
00:46:27 --> 00:46:29 warmer. So yeah, tropical rain forest
00:46:29 --> 00:46:31 and probably dinosaurs. dinosaurs was
00:46:31 --> 00:46:32 the next thing that came up. You're
00:46:32 --> 00:46:34 right. Yes. Some scientists even
00:46:34 --> 00:46:35 postulated that, well, if you've got
00:46:35 --> 00:46:37 tropical rainforest, you've probably got
00:46:37 --> 00:46:38 dinosaurs. How they reached that
00:46:38 --> 00:46:40 conclusion, I don't know, but that was
00:46:40 --> 00:46:41 Yeah, that was very common back in the
00:46:41 --> 00:46:43 50s and 60s. A lot of scientists
00:46:43 --> 00:46:45 supported that idea. It was it was it
00:46:45 --> 00:46:46 was speculation and I mean, it was sort
00:46:46 --> 00:46:48 of a very uneducated guess, but you
00:46:48 --> 00:46:49 know, you can sort of understand. It's
00:46:50 --> 00:46:51 like the canals on Mars, isn't it? Yeah,
00:46:51 --> 00:46:54 the canals on Mars. See, here's the it's
00:46:54 --> 00:46:55 hard for people these days, I suppose,
00:46:55 --> 00:46:58 to think about this, but you go back to
00:46:58 --> 00:47:00 the turn of the 19th, 20th century, you
00:47:00 --> 00:47:01 know, go back to the year 1900 or
00:47:02 --> 00:47:04 whatever. It was widely assumed that
00:47:04 --> 00:47:05 there would be life on the other planets
00:47:05 --> 00:47:07 because if there's life on Earth, why
00:47:07 --> 00:47:08 wouldn't there be life on other planets?
00:47:08 --> 00:47:10 Because we didn't know what those other
00:47:10 --> 00:47:11 planets were like back then. We didn't
00:47:11 --> 00:47:14 have the technology to really establish
00:47:14 --> 00:47:16 uh what the atmospheres were made of um
00:47:16 --> 00:47:18 and what the temperatures might be, all
00:47:18 --> 00:47:19 that sort of thing. At least we're not
00:47:20 --> 00:47:22 in great precision. And so even when the
00:47:22 --> 00:47:25 first NASA spacecraft were getting to um
00:47:25 --> 00:47:27 Mars, it was you know still people were
00:47:27 --> 00:47:28 thinking well that's going to show
00:47:28 --> 00:47:29 things on Mars, you know, might show
00:47:30 --> 00:47:31 vegetation or whatever. But then the
00:47:31 --> 00:47:33 first picture started coming back which
00:47:33 --> 00:47:35 just showed a desert world with craters
00:47:35 --> 00:47:38 and things. So um for a long time people
00:47:38 --> 00:47:40 just assumed that there there was going
00:47:40 --> 00:47:41 to be life on the other other world.
00:47:42 --> 00:47:43 Then we started to learn, you know, that
00:47:43 --> 00:47:44 Mars is actually really cold. It's got a
00:47:44 --> 00:47:47 thin atmosphere and Venus has got a
00:47:47 --> 00:47:49 runaway greenhouse effect. So it's very
00:47:49 --> 00:47:50 very hot and the air pressure would be
00:47:50 --> 00:47:52 very very intense. You know about 90
00:47:52 --> 00:47:55 atmosphere and temperatures of over 400°
00:47:55 --> 00:47:57 Celsius 450 something degrees Celsius
00:47:57 --> 00:47:59 and possible sulfuric acid rain from the
00:47:59 --> 00:48:02 clouds. So snow on the cloud tops by the
00:48:02 --> 00:48:03 way we've got a we've got a far more
00:48:04 --> 00:48:06 sophisticated idea of what things are
00:48:06 --> 00:48:07 like out there now. But yeah back in the
00:48:07 --> 00:48:08 back in the early days when we didn't
00:48:08 --> 00:48:10 really know people just assume. So but
00:48:10 --> 00:48:12 you know goodness knows how many things
00:48:12 --> 00:48:14 we take for granted as being true right
00:48:14 --> 00:48:17 now this year in 2025 which 100 years
00:48:17 --> 00:48:19 from now or 50 years from now uh will be
00:48:19 --> 00:48:22 considered complete nonsense. So um I'm
00:48:22 --> 00:48:23 not critical of um people who thought
00:48:24 --> 00:48:26 various things in in past times when
00:48:26 --> 00:48:28 they were had some reason to think that
00:48:28 --> 00:48:29 might have been it's it's when you get
00:48:29 --> 00:48:31 people who just totally ignore the
00:48:31 --> 00:48:33 evidence or you know try and work their
00:48:33 --> 00:48:34 way around the evidence. So for
00:48:34 --> 00:48:36 instance, PL look at finding his canals
00:48:36 --> 00:48:38 on Mars when no one else could see them,
00:48:38 --> 00:48:39 but he just sort of stuck with it
00:48:39 --> 00:48:40 because he was he was sure that there
00:48:40 --> 00:48:42 were canals on Mars and no one else
00:48:42 --> 00:48:43 could see them. So um that that's when
00:48:43 --> 00:48:45 you have problems. Well, the problem was
00:48:45 --> 00:48:47 he didn't translate Chaperelli's
00:48:47 --> 00:48:49 original comments correctly. Chaperelli
00:48:49 --> 00:48:50 was talking about canali, but he didn't
00:48:50 --> 00:48:52 mean canals. He meant channels.
00:48:52 --> 00:48:54 Something like water channels or river,
00:48:54 --> 00:48:55 that kind of thing. Yeah. They got
00:48:55 --> 00:48:57 translated into canals, which in English
00:48:57 --> 00:48:59 means an artificial. Yeah. Well, they
00:48:59 --> 00:49:01 were building a huge canal network in
00:49:01 --> 00:49:03 England at the time, weren't they? Yeah.
00:49:03 --> 00:49:05 Yeah. And um and he was he was
00:49:05 --> 00:49:06 essentially seeing what he wanted to
00:49:06 --> 00:49:08 see. He got it into his mind and and
00:49:08 --> 00:49:10 that was the end of it. And um yeah,
00:49:10 --> 00:49:11 well that I mean that's that's a that's
00:49:11 --> 00:49:13 just a human failing, isn't it really?
00:49:13 --> 00:49:14 And on that philosophical note, Stuart,
00:49:14 --> 00:49:16 we just solved all the world's problems
00:49:16 --> 00:49:18 once again. Aren't we good? And and I'll
00:49:18 --> 00:49:19 see you next month. That's science
00:49:19 --> 00:49:36 editor Jonathan Nally and this is
00:49:36 --> 00:49:39 Spacetime and that's the show for now.
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