S27E132: Betelgeuse's Binary Mystery, Branson's Balloon Adventure, and November Skywatch

[00:00:00] This is SpaceTime Series 27 Episode 132, for broadcast on the 1st of November 2024. Coming up on SpaceTime, could Betelgeuse actually be two stars? Richard Branson to co-pilot the first manned flight for Space Perspective. And they haven't put anything in orbit for half a century, but Australia is looking at developing more spaceports. All that and more coming up on SpaceTime.

[00:00:27] Welcome to SpaceTime with Stuart Gary.

[00:00:46] A new study has raised the possibility that the red supergiant Betelgeuse may actually be a binary star system.

[00:00:53] Now, if that's the case, it means the star may not be on the brink of exploding as a supernova after all.

[00:00:59] Located between 530 and 643 light years away, Betelgeuse is the brightest star of the constellation Orion,

[00:01:06] the 10th brightest star in our night skies, and one of the largest and most luminous stars visible with the unaided eye.

[00:01:13] Commonly called Betelgeuse, don't say it three times, its name before centuries of tortured mispronunciations started out as Ibtal Yalza,

[00:01:22] meaning hand of the big man in Arabic, the big man being Orion the Hunter.

[00:01:27] Betelgeuse began its life about 10 million years ago as a spectral type OB blue star, making it one of the largest and most luminous main sequence stars.

[00:01:36] Calculations of Betelgeuse's mass range from slightly under 10 to a little over 20 times that of our Sun,

[00:01:41] with some 100,000 times the Sun's brightness and around 1100 times its diameter.

[00:01:46] If Betelgeuse were at the location of the Sun at the centre of our solar system,

[00:01:51] its surface would extend almost out as far as Jupiter, engulfing the orbits of Mercury, Venus, Earth, Mars and the main asteroid belt.

[00:01:58] It's now a bloated old semi-regular variable red supergiant.

[00:02:03] Red supergiant are the largest stars in the universe in terms of their volume.

[00:02:08] Eventually they explode as core collapse supernovae, ending up as neutron stars or stellar mass black holes.

[00:02:15] And Betelgeuse is expected to explode any day now, which in astronomical terms could mean a million years from now, or it could mean tomorrow.

[00:02:22] When it does explode, it will temporarily outshine all the other stars in the galaxy, and it will be clearly visible in the daytime sky here on Earth.

[00:02:30] The last star seen by humans to go supernovae in our galaxy was Tycho's star.

[00:02:35] That was way back in 1572, long before the invention of the telescope.

[00:02:40] However, these new observations mean Betelgeuse may not be on the brink of exploding after all.

[00:02:45] Astronomers can predict when a star will die by effectively checking its pulse.

[00:02:50] What happens is stars get brighter and dimmer, pulsing like a heartbeat, counting down to an eventual supernova explosion.

[00:02:57] However, the new observations on Betelgeuse reported in the Astrophysical Journal

[00:03:01] suggested the pulsing of this star could be caused by an unseen companion star orbiting Betelgeuse.

[00:03:07] Formerly named Alpha Orion b, this tentative second star would be acting like a sort of snow plough,

[00:03:14] orbiting Betelgeuse and pushing light-blocking dust out of the way, temporarily making Betelgeuse seem brighter.

[00:03:19] That's the pulse.

[00:03:21] The studies lead author, Jared Goldberg from the Flatiron Institute, says he's already ruled out every other intrinsic source for variability,

[00:03:28] and the only hypothesis that seemed to fit the observations is that Betelgeuse has a companion.

[00:03:34] Now, to back that up, Goldberg and colleagues observed that Betelgeuse had two heartbeats,

[00:03:39] one that pulses on a timescale of a little longer than an Earth year,

[00:03:42] and one that pulses on a timescale of about six Earth years.

[00:03:46] One of those heartbeats is Betelgeuse's fundamental mode,

[00:03:49] a pattern of brightening and dimming that's intrinsic to the star itself.

[00:03:53] If the star's fundamental mode is its long-scale heartbeat,

[00:03:56] then Betelgeuse could be ready to blow sooner than expected.

[00:03:59] However, if its fundamental mode is its short-scale heartbeat,

[00:04:03] as several studies suggest, then its longer heartbeat is a phenomenon called a long secondary period.

[00:04:08] In that case, the longer brightening and dimming would be caused by something external to the star itself.

[00:04:14] Now, scientists still don't know for sure what's causing the long secondary periods.

[00:04:18] But one of the leading theories is that they arise when a star is a companion that's circling it,

[00:04:23] and barrels through cosmic dust being produced and expelled by the primary star.

[00:04:27] This displaced dust would alter how much starlight reaches an observer on Earth,

[00:04:32] changing the star's apparent brightness.

[00:04:35] Goldberg and colleagues explored whether other processes could have caused the long secondary period,

[00:04:39] such as the churning of the star's interior,

[00:04:42] or periodic changes in the star's powerful magnetic field.

[00:04:45] After combining direct observations of Betelgeuse with advanced computer models

[00:04:49] that simulate the star's activity,

[00:04:51] the authors concluded that a secondary star is by far the most likely explanation.

[00:04:56] Goldberg says that if there's no companion,

[00:04:58] it means that something way weirder must be going on,

[00:05:01] something impossible to explain with current physics.

[00:05:04] The authors have yet to explain what the so-called Betelbuddy is,

[00:05:07] but they assume it's a star about twice the mass of our Sun.

[00:05:11] A more exotic hypothesis is that the companion's a neutron star,

[00:05:14] the core of a star that's already gone supernova.

[00:05:17] However, if that's the case, you'd expect to see evidence of this with X-ray observations,

[00:05:21] and they're not showing it.

[00:05:22] So the authors will now try to take images of Betelbuddy with telescopes

[00:05:26] as there's a potential window of visibility around December the 6th.

[00:05:30] That's just a month away.

[00:05:32] They'll need to confirm that Betelbuddy really does exist,

[00:05:35] since their results are based on inference, not on direct detection.

[00:05:39] Needless to say, we'll keep you informed.

[00:05:42] This is Space Time.

[00:05:43] Still to come, Richard Branson to co-pilot a new stratospheric balloon flight.

[00:05:48] And although we haven't launched an orbital mission for over half a century,

[00:05:51] Australia is looking at developing even more spaceports.

[00:05:55] All that and more still to come on Space Time.

[00:06:13] It's been announced that Virgin boss Richard Branson

[00:06:16] will co-pilot Space Perspective's first stratospheric balloon flight.

[00:06:20] Last month, the Florida-based company undertook an unmanned test flight

[00:06:24] of their high-altitude balloon and gondola,

[00:06:26] which will eventually take space tourists to altitudes of over 100,000 feet.

[00:06:30] That's 30 kilometers above the ground.

[00:06:32] Now, although that's nowhere near the edge of space,

[00:06:35] it's high enough to allow occupants to see the curvature of the Earth

[00:06:38] under a black sky even in broad daylight.

[00:06:40] The system uses a hydrogen-filled balloon and a pressurized gondola.

[00:06:45] The six-hour stratospheric flight will avoid the high G-forces

[00:06:48] of rocket-powered space tourism flights, providing a far more gentle experience

[00:06:53] that will include meals and Wi-Fi.

[00:06:55] It will offer up to eight passengers at a time breathtaking views through panoramic windows.

[00:07:00] And there's no weightlessness, so no risk of space sickness.

[00:07:04] Branson, who undertook record-breaking Atlantic and Pacific Ocean balloon crossings

[00:07:08] and established the Virgin Group, already operates Virgin Galactic,

[00:07:12] which takes space tourists to the very edge of space.

[00:07:15] This is space time.

[00:07:17] Still to come, Australia looking at developing more spaceports,

[00:07:21] and the giant spiral galaxy M31 Andromeda, the Crab Nebula M1,

[00:07:26] and three meteor showers are among the highlights of the November night skies on Skywatch.

[00:07:46] Although Australia hasn't put anything into orbit since the glory days of the Wilma rocket range

[00:07:50] over half a century ago, lands are afoot for new spaceports,

[00:07:54] with both Western Australia and Queensland the latest to make proposals.

[00:07:58] Spaceport Australia has announced plans to construct a spaceport on the Cape York Peninsula

[00:08:03] in far north Queensland.

[00:08:04] The company's already announced a $30 million deal to acquire two air surveillance radars for the project.

[00:08:10] The deal would see the technology arrive by the end of 2026.

[00:08:14] Former Australian Prime Minister Scott Morrison has been appointed chairman of the new company.

[00:08:20] Meanwhile, on the other side of the country,

[00:08:22] the Western Australian government appears to be hinting at the idea of establishing its own spaceport.

[00:08:26] The government's new space industry strategy claims the state's vast coastline

[00:08:31] and minimal air traffic would make it an ideal location for a space launch and return facility.

[00:08:36] It's not the first time a spaceport has been proposed in Western Australia.

[00:08:40] Another company was looking at polar rocket launches from Albany on the Great Australian Bight back in 2022.

[00:08:47] But the new plan claims Western Australia would be an ideal location for communications,

[00:08:52] tracking and launch facilities offering a range of advantages in optimal environmental conditions.

[00:08:57] The statement claims the state's clear skies, large arid areas, minimal radio interference

[00:09:03] and location around 120 degrees apart in longitude to Western Europe and North America

[00:09:08] would provide an ideal world-class location for hosting space ground infrastructure.

[00:09:13] And of course, the state already hosts dozens of national and international facilities

[00:09:17] that support global coverage of space assets, space communications

[00:09:21] as well as space situational awareness and positioning navigation and timing facilities.

[00:09:26] The Western Australia space industry strategy has already seen over a billion dollars

[00:09:31] invested or committed to Western Australia's space sector since 2018.

[00:09:36] Australia's already home to five spaceports.

[00:09:38] There's Equatorial Launch Australia's Arnhem Land Space Centre in the Northern Territory,

[00:09:43] Gilmore Space Technologies Orbital Space Port in North Queensland in Bowen,

[00:09:47] Southern Launch's Orbital Whalers Wave Facility

[00:09:49] and Suborbital Canimber Test Range in South Australia

[00:09:52] and of course there's the Woomera rocket range also in SA.

[00:09:57] This is Space Time.

[00:10:15] And time now to turn our eyes to the skies and check out the celestial sphere for November on Skywatch.

[00:10:21] High in the northern skies of November, you'll find the constellation Pegasus,

[00:10:26] the Mesopotamian and Etruscan mythical winged horse

[00:10:29] who was born from the blood of Medusa the Gorgon after she was slain by Perseus.

[00:10:34] The brightest star in Pegasus is the orange supergiant Epsilon Pegasi located some 690 light years away.

[00:10:41] It's estimated to have about 185 times the sun's radius and 12 times its mass.

[00:10:47] Epsilon Pegasi together with the stars Markab, Al Janibe, Shahid and Alpha Andromeda

[00:10:53] forms the asterism or pattern of stars known as the Great Square of Pegasus,

[00:10:58] a bunch of bright naked ice stars shaped like a square.

[00:11:01] One of the stars in this constellation is 51 Pegasi.

[00:11:05] 51 Pegasi is a sun-like star located 51 light years away.

[00:11:10] On October the 6th 1995, astronomers announced the discovery of an exoplanet orbiting the star.

[00:11:16] It was the first ever confirmed detection of a planet orbiting another star.

[00:11:20] The planet has around half the mass of Jupiter and is thought to be a gas giant.

[00:11:25] But it wasn't what scientists were expecting.

[00:11:28] The planet orbits the star in just four Earth days.

[00:11:31] That's much closer than Mercury's 88-day orbit around the sun.

[00:11:34] Because it orbits so close to the star, 51 Pegasi b as it's called,

[00:11:39] experiences temperatures estimated to be around 1200 degrees Celsius.

[00:11:43] Now at the time of its discovery, this close distance was not compatible with theories of planetary formation

[00:11:48] and resulted in a lot of discussion among scientists about the idea of planetary migration.

[00:11:55] However, since its discovery, numerous other so-called hot Jupiters have been detected,

[00:11:59] pretty much confirming planetary migration to be real.

[00:12:03] By the way, a light year?

[00:12:04] Well that's the distance a photon can travel in a year at the speed of light,

[00:12:08] which is some 300,000 kilometers per second in a vacuum and the ultimate speed limit of the universe.

[00:12:14] Also visible in Pegasus is the M15 or NGC 7078 globular cluster, which is located around 33,600 light years away.

[00:12:25] Globular clusters are tight balls containing thousands of stars,

[00:12:29] which are all originally formed at the same time out of the same molecular gas and dust cloud.

[00:12:35] M15 is estimated to be around 12 billion years old, making it one of the oldest known globular clusters.

[00:12:41] And it contains around 100,000 stars, making it one of the most densely packed globular clusters in the entire Milky Way galaxy.

[00:12:48] Its cores undergone a contraction known as core collapse, and it has a central density cusp with an enormous number of stars,

[00:12:56] orbiting very rapidly around what appears to be a central black hole.

[00:13:01] M15 also contains at least 112 variable stars, eight pulsars including one double neutron star system,

[00:13:07] and the first ever planetary nebula found in a globular cluster.

[00:13:12] Now if you're in or near the Northern Hemisphere and away from city lights,

[00:13:16] you'll notice a fuzzy patch of light right next to Pegasus.

[00:13:19] This is the giant spiral galaxy, M31 Andromeda.

[00:13:26] Andromeda is the biggest galaxy in our local galactic group.

[00:13:30] Located some 2.5 million light years away, Andromeda consists of more than a trillion stars,

[00:13:36] around twice the number found in the Milky Way.

[00:13:38] And it's huge, some 220,000 light years across.

[00:13:44] Based on current estimates, Andromeda appears to have more older stars than the Milky Way.

[00:13:49] It also has far less new star production going on than our galaxy.

[00:13:53] And the rate of supernovae in the Milky Way is also about double that in Andromeda.

[00:13:59] Andromeda is surrounded by a large massive halo of hot gas and plasma,

[00:14:03] estimated to contain at least half the mass of the stars in the galaxy.

[00:14:07] This nearly invisible halo stretches about a million light years from its host galaxy.

[00:14:12] That's almost halfway towards the Milky Way.

[00:14:16] Using a good pair of binoculars or a backyard telescope,

[00:14:19] you'll see dark dust lanes in Andromeda's spiral arms,

[00:14:22] and you'll see its bright central galactic core.

[00:14:26] Now over time, Andromeda will become a lot clearer.

[00:14:29] That's because it's getting closer.

[00:14:31] You see, the Milky Way and Andromeda are expected to collide in about 3.7 to 4.5 billion years from now.

[00:14:39] The two spirals eventually merging to form a new giant elliptical galaxy.

[00:14:44] What that means for the future of the Earth, the Sun and our solar system is a matter of great ongoing debate.

[00:14:51] The gravitational tidal perturbations from the encounter could rip our solar system apart,

[00:14:56] or even fling us out into intergalactic space.

[00:15:00] At this stage, only time will tell.

[00:15:02] Now looking to the east and slightly south of Pegasus,

[00:15:06] you'll see the ancient constellation of Cetus, the Great Whale Sea Monster.

[00:15:11] The brightest star in the constellation is Beta Seti or Denebcatos,

[00:15:16] an orange giant located 96 light years away.

[00:15:19] The name Denebcatos means the whale's tail.

[00:15:22] Another one of the stars in Cetus is Mira, the first variable star ever discovered.

[00:15:28] Located some 420 light years away,

[00:15:31] Mira pulsates in brightness over a period of 332 days,

[00:15:35] changing in diameter from around 400 to 500 times the diameter of our Sun.

[00:15:40] Also visible is Alpha Seti, traditionally called Menka the nose.

[00:15:45] It's a red-hued giant star some 220 light years away.

[00:15:49] It's actually a double star, with a secondary 93 seti being a blue-white star some 440 light years away.

[00:15:56] Also in Cetus, located some 11.9 light years away,

[00:16:00] is the yellow dwarf star Tau Seti, the nearest sun-like star to the Earth other than the Sun.

[00:16:07] Astronomers describe stars in terms of spectral types.

[00:16:11] It's a classification system based on temperature and other characteristics.

[00:16:15] The hottest, most massive and most luminous stars

[00:16:18] are known as Spectral Type O blue stars.

[00:16:21] That's followed by Spectral Type B blue-white stars,

[00:16:24] then Spectral Type A white stars,

[00:16:27] Spectral Type F whitish yellow stars,

[00:16:29] then comes Spectral Type G yellow stars.

[00:16:32] That's where our Sun fits in.

[00:16:34] Slightly cooler are Spectral Type K orange stars,

[00:16:37] and then the coolest and least massive stars known,

[00:16:40] are Spectral Type M red stars.

[00:16:42] Each Spectral classification can then further be subdivided,

[00:16:46] using a numeric digit to represent temperature,

[00:16:49] with zero being the hottest and nine the coolest.

[00:16:51] And then you add a Roman numeral to represent luminosity.

[00:16:55] So at the end of all that, our Sun is classified as a G2V,

[00:16:59] or if you prefer G25, yellow dwarf star.

[00:17:03] Also included in the Stellar classification system are Spectral Types L, T and Y,

[00:17:08] which are assigned to failed stars known as brown dwarves,

[00:17:11] some of which were actually born as Spectral Type M red stars,

[00:17:15] but then became brown dwarves after losing some of their mass.

[00:17:19] Brown dwarves fit in a unique category between the largest planets,

[00:17:23] which are about 13 times the mass of Jupiter,

[00:17:25] and the smallest spectrotype M red stars,

[00:17:28] which can be 75 to 80 times the mass of Jupiter,

[00:17:31] or 0.08 solar masses.

[00:17:35] South of Cetus, you'll find the brilliant star Achenar,

[00:17:38] which means the river's end, and it marks the end of the river Aridinus.

[00:17:42] Achenar is a binary system comprising Alpha Aridinus,

[00:17:45] which is the brightest star of point of light in

[00:17:48] and lying at the southern tip of the constellation of Aridinus.

[00:17:51] The two components of Alpha Aridinus are designated Alpha Aridinus A and Alpha Aridinus B,

[00:17:56] and they're located about 139 light years away.

[00:17:59] Of the 10 apparent brightest stars in our night sky,

[00:18:02] Alpha Aridinus is the hottest and bluest in colour.

[00:18:05] That's due to Achenar being a Spectral Type B main sequence star.

[00:18:09] Achenar also has an unusually rapid rotational velocity,

[00:18:13] causing it to be quite oblate in shape.

[00:18:15] The second star in the system is a smaller Spectral Type A white star,

[00:18:19] and orbits the primary star at a distance of around 12 astronomical units.

[00:18:24] Follow Aridinus towards the east,

[00:18:26] and you'll see the magnificent constellation Orion the Hunter,

[00:18:30] a familiar signpost for southern summer skies.

[00:18:33] To the west of Orion is the constellation Taurus the Bull,

[00:18:37] and located in Taurus is M1 the Crab Nebula.

[00:18:41] It's the remnant of a star which Chinese astronomers saw explode as a supernova

[00:18:46] on July the 4th in the year 1054.

[00:18:49] They recorded the sudden appearance of a new star on their sky charts

[00:18:53] at the exact position of the Crab Nebula.

[00:18:56] The supernova appeared brighter than the planet Venus for weeks on end,

[00:19:00] before finally fading completely from view after almost two years.

[00:19:05] The Crab Nebula is located some 7,000 light years away.

[00:19:09] It's expanding at a rate of over 5 million kilometers per hour.

[00:19:14] At the heart of the nebula is a rapidly spinning neutron star or pulsar,

[00:19:19] rotating some 30 times every second.

[00:19:21] It's emitting radiation in all wavelengths from gamma rays and X-rays,

[00:19:25] through ultraviolet, optical and infrared, and on into radio waves.

[00:19:30] Observations indicate the pulse's spin rate is slowing down,

[00:19:34] and it will fall to just half its current rotational rate in the next thousand years.

[00:19:40] November is also a great time to check out the Pleiades or Seven Sisters,

[00:19:44] one of the nearest and most spectacular open star clusters to Earth.

[00:19:48] Also known as M45, the Pleiades are located in the constellation Taurus.

[00:19:54] Now, depending on whose measurements you prefer,

[00:19:56] the Pleiades are located somewhere between 118 and 137 parsecs away,

[00:20:02] a parsec being 3.26 light years.

[00:20:05] The Pleiades are composed of mostly hot blue-white stars.

[00:20:09] Amazingly, different cultures in vastly different parts of the world

[00:20:13] all describe the Pleiades as Seven Sisters or Seven Women,

[00:20:17] possibly some sort of ancient throwback to very early human civilization.

[00:20:22] Just like October, November also sees three meteor showers.

[00:20:27] There's the November Orionids, as well as the Taurids and the Leonids.

[00:20:31] Although peaking in late October,

[00:20:34] the Orionids continue to sprinkle down during the start of November,

[00:20:37] and are usually at their best in the wee small hours before dawn.

[00:20:41] They're generated by the debris trail left behind by the comet Halley,

[00:20:45] and appear to radiate out from the direction of the constellation Orion the Hunter,

[00:20:50] hence their name.

[00:20:51] The Taurids are generated by the comet Enki,

[00:20:54] and as their name suggests,

[00:20:56] they appear to radiate out from the constellation Taurus the Bull.

[00:21:00] Now, Enki and the Taurids are believed to be the remnants of a much larger comet,

[00:21:04] which disintegrated sometime in the past 20,000 to 30,000 years,

[00:21:08] breaking into several pieces,

[00:21:10] and releasing material by normal cometary activity,

[00:21:13] and maybe occasionally through close encounters with the gravitational tidal force of the Earth and other planets.

[00:21:19] In fact, the cometary stream of material from the Taurids is the largest in the inner solar system.

[00:21:25] And being so spread out, the Earth takes several weeks to pass through it all.

[00:21:30] That means there's an extended period of meteor activity,

[00:21:33] compared to the much smaller periods of activity for other meteor showers.

[00:21:36] Interactions with the giant gas planet Jupiter have also caused the Taurids to be segmented into separate northern and southern streams.

[00:21:44] The southern Taurids usually last from around September 25th to around November 25th,

[00:21:50] while the northern Taurids go from October 12th to around December 2nd.

[00:21:55] The Taurids are usually quite diffuse, only producing about 7 meteors per hour.

[00:22:00] However, they're composed of far more massive material – think of pebbles instead of dust grains –

[00:22:05] and so they tend to produce a high percentage of very bright meteors known as fireballs,

[00:22:10] produced by the larger meteoroids burning through the atmosphere.

[00:22:14] The southern Taurids should be putting on their best show just after midnight around now.

[00:22:19] The third meteor shower in November are the Leonids, which peak around November 18th.

[00:22:24] They usually produce around 15 meteors an hour,

[00:22:27] but have been known to occasionally produce some spectacular meteor storms.

[00:22:31] With showers in 1999, 2001 and 2002 producing around 3,000 Leonid meteors per hour.

[00:22:40] But one of the best had to have been the Leonids meteor shower of 1966,

[00:22:44] which generated literally thousands of meteors per minute, falling like illuminated rain.

[00:22:50] The Leonids are usually picked up after midnight, with peaks occurring just before dawn.

[00:22:56] Produced by debris from the comet Temple Tuttle, the Leonids radiate out from the constellation Leo the Lion.

[00:23:02] And they're a fast-moving stream, encountering the path of the Earth at 72 km per second.

[00:23:08] Larger Leonids, which are about 10 mm across, can have a mass of half a gram,

[00:23:13] and are known to generate really bright meteors.

[00:23:16] It's been calculated that the annual Leonids meteor shower can deposit 12 to 13 tons of particles across the planet.

[00:23:23] Jonathan Nally from Sky and Telescope magazine joins us now for the rest of our tour of the November night skies.

[00:23:30] G'day Stuart. Well, where I live, we're heading towards summer.

[00:23:33] I live in the southern hemisphere, of course.

[00:23:34] Summer's coming up, the weather's becoming much nicer, the evenings are becoming warmer.

[00:23:38] Only problem is that for many of us, including myself, we've got daylight saving to contend with,

[00:23:42] so you've got to wait later in the evening for the sky to get dark.

[00:23:44] But, well, win some, you lose some.

[00:23:46] After the sun has set, we have a short window to get our last glimpses for the year of the mighty constellation Scorpius and Sagittarius.

[00:23:54] The front half of the scorpion has already disappeared below the western horizon after sunset,

[00:23:58] but the tail end with the sting is still poking upwards into the sky, so you can still see that.

[00:24:02] If you're looking for the Southern Cross, you won't have much luck during the pre-midnight hours during November.

[00:24:07] At this time of year, it's upside down and either very low on the southern horizon or below the horizon,

[00:24:12] depending on which city you're living in and how far south you are.

[00:24:15] But if you're up and about in the hours before dawn, you will be able to see it.

[00:24:19] It will be lying on its left-hand side, sort of low in the southeast, so it looks like a pike shape.

[00:24:24] And it's quite small. The Southern Cross is actually the smallest constellation,

[00:24:27] so don't go out expecting to see something really big.

[00:24:29] If you hold your hand out at arm's length, you can cover it up.

[00:24:31] It's the smallest constellation.

[00:24:33] Now, if you have really dark star waves, if you're somewhere where you don't have much light pollution,

[00:24:37] you might be able to make out a dark patch in the Milky Way right next to the Southern Cross.

[00:24:42] This is called the coal shack.

[00:24:44] That's its nickname, the coal shack.

[00:24:46] It's a huge region of interstellar gas and dust that's out there in space,

[00:24:50] and it's blocking out the stars of the Milky Way behind it.

[00:24:53] Originally, people thought, no, this might be a hole in the Milky Way,

[00:24:56] and we're looking straight through to the other side, but then they realised,

[00:24:59] no, it's just a big dark cloud in the foreground, basically, with the Milky Way behind it.

[00:25:03] There are some stars in front of the coal shack, so it's not completely black,

[00:25:07] but you do need some dark skies, country skies, or just away from light pollution in order to see that.

[00:25:13] In the early morning, if you're still out there looking for the Southern Cross,

[00:25:15] you should also be able to see two bright stars down near the southern horizon.

[00:25:18] These are known as the two pointers, or the pointers,

[00:25:21] because if you draw an imaginary line between them and then keep that line going for a short distance,

[00:25:26] it points more or less towards the Southern Cross.

[00:25:29] One of those two stars is the famous Alpha Centauri, and it's actually a triple star system

[00:25:34] and the closest star system to our solar system. It's only just over four light years away.

[00:25:39] Alpha Centauri is actually a double star.

[00:25:42] There's two stars going around each other very close,

[00:25:44] and the third star in this overall triple system is very, very small, very faint.

[00:25:50] You can't see it with the naked eye.

[00:25:52] You need a telescope and you need to know exactly where to see it,

[00:25:54] but it actually is the closest star to Earth, up in the Sun.

[00:25:57] It's called Proxima Centauri.

[00:25:59] Now in the evening, if you look in the southeast, you'll see a very bright star.

[00:26:02] This is Canopus, the brightest star in the constellation Carina,

[00:26:06] and in fact the second brightest star in the night sky.

[00:26:08] In color, it is essentially white, although some people, myself included,

[00:26:12] think it has a slightly yellowish tinge.

[00:26:14] That's a combination of eyesight, and I think it does.

[00:26:18] It's not purely white.

[00:26:19] And also, very often when you're looking at it, it's down towards the horizon,

[00:26:22] so you're getting a bit of atmospheric murk in the way,

[00:26:25] so that tends to change its color a little bit too.

[00:26:27] Canopus is about 310 light-years from Earth, which is not very far in space terms.

[00:26:32] And like many stars, Canopus is huge.

[00:26:35] It's really big.

[00:26:36] That's not the biggest, but it's big.

[00:26:38] It's about 70 times, get this, it's about 70 times wider than our Sun,

[00:26:42] and it's more than 10,000 times brighter.

[00:26:45] And the only reason it's not as bright as the Sun in our night sky

[00:26:49] is because it's 310 light-years away.

[00:26:51] If it was much closer, it would be just dazzling.

[00:26:54] Now, higher up above Canopus, you see another bright star, quite high up in fact.

[00:26:58] It's called Aconar, and it's the brightest star in the constellation of Eridanus,

[00:27:03] a constellation most people never heard of, the constellation of the river.

[00:27:06] And this is the ninth brightest star in all of the night sky.

[00:27:08] And one of its claims to fame, you can't see this, but the scientists have worked it out,

[00:27:13] is that it's spinning so rapidly on its axis that its equator is sort of bulging out,

[00:27:18] and the poles are flattened.

[00:27:19] It's not a sphere like most other stars, but it's become oblate, sort of flattened.

[00:27:24] So, yes, stretched out around its equator and sort of squashed at the poles,

[00:27:28] because it's spinning really fast.

[00:27:29] Now, as the evening is progressing, when we get towards midnight,

[00:27:33] you'll see that the other half of the Milky Way is rising in the east,

[00:27:37] because at the beginning of the evening, the first half of the Milky Way, if you want to call it,

[00:27:41] is right on the western horizon, and it goes down very quickly.

[00:27:43] But late in the evening, towards midnight, you see the other half of the Milky Way coming up in the east,

[00:27:47] and it's bringing with it some of the best stars and constellations.

[00:27:51] For us in the southern hemisphere, we know this is the sign that summer's approaching.

[00:27:54] For our friends in the northern hemisphere, they know it's the sign that winter is approaching.

[00:27:56] So first, low down in the east, there's Sirius.

[00:27:59] And this is the brightest star in the constellation Canis Major, or the greater dog.

[00:28:04] And Sirius is the brightest star in the night sky.

[00:28:07] Around to its left a bit is the fantastic constellation Orion.

[00:28:11] There are many amazing sights.

[00:28:13] You've got these two bright stars called Rigel and Betelgeuse.

[00:28:16] We've got three little stars in a row that form the belt of Orion.

[00:28:20] Orion stands for the hunter.

[00:28:22] So this is the hunter's belt.

[00:28:23] And then hanging down from the belt are a couple of other stars and a fuzzy patch.

[00:28:29] Well, that is an enormous star-forming region, 1500 light years from Earth.

[00:28:34] And it's just amazing that we can see these things just with the unaided eye.

[00:28:38] It really, really is.

[00:28:39] It might not look impressive, but when you think about what it is and what you've just seen,

[00:28:44] it's really quite remarkable.

[00:28:45] So that's around to the left of Sirius.

[00:28:48] So if you keep going further around the left, around to the north,

[00:28:51] we get to the constellation Taurus, which is pretty easy to make out because it has a wedge-shaped group of stars,

[00:28:57] a star cluster called the Hyades.

[00:28:59] And there's a bright red star there called Aldebaran.

[00:29:03] Not far from the Hyades and Aldebaran is another easily seen group of stars called the Pleiades,

[00:29:09] or the Seven Sisters.

[00:29:10] Now, if you get a pair of binoculars onto this one, you will gasp in wonder, I assure you,

[00:29:14] because it looks really pretty through a pair of binoculars.

[00:29:17] You don't even need a telescope.

[00:29:19] Seven Sisters is just made because most people with average eyesight can make out seven of the stars.

[00:29:24] There are actually hundreds and hundreds of stars in this star cluster, but most of them are quite faint.

[00:29:28] But if you get a pair of binoculars onto it, you'll see many more than you can with a naked eye.

[00:29:32] It really looks lovely.

[00:29:34] Now, let's look at the planets.

[00:29:36] Mercury is actually readily visible all this month, which is not common.

[00:29:40] Very often, Mercury is very low on the horizon and only for a week or two,

[00:29:44] and you don't really get to see it.

[00:29:45] But this month, fortunately, we're going to see it quite easily.

[00:29:48] You'll find it above the western horizon after the sun has set.

[00:29:51] So where the sun goes down, once it's gone down below the horizon and the stars are starting to get a bit dark,

[00:29:56] even in the twilight, in fact, you'll see what looks like a small bright star,

[00:30:01] and that's Mercury, but it is, of course, a planet.

[00:30:04] It should be quite easy to spot.

[00:30:06] Higher up, sort of straight up from that, from Mercury, is a much brighter light,

[00:30:11] and that's Venus, and you just simply can't miss Venus.

[00:30:13] It's so bright.

[00:30:14] It's actually brighter than those two bright stars I mentioned earlier, Sirius and Canopus.

[00:30:19] Now, Saturn is almost overhead for people like me who live at mid-southern latitudes.

[00:30:25] It looks like a medium-brightness star, in inverted commas, and it's got a yellowish tinge.

[00:30:29] And because it's so far away in space, it doesn't appear to move much from night to night.

[00:30:33] In fact, you really won't see any movement night to night,

[00:30:35] because it's going so slowly through the night sky.

[00:30:38] And unlike Mercury, which you should notice has changed position as each night rolls around,

[00:30:42] you'll see Mercury from night to night, and Mercury will have changed position a bit.

[00:30:45] It got a bit higher, and then later than month, it'll get a bit lower.

[00:30:48] But Saturn, it's basically going to stay in the one spot and move with the stars as the Earth rotates.

[00:30:55] Now, throughout stargaving after midnight, and the wee small hours, maybe you're finishing a night shift or something,

[00:31:00] or you're coming home from a party, you'll find Jupiter, big and bright, not far from that star Aldebaran I mentioned earlier, actually.

[00:31:06] So Aldebaran looks red, and Jupiter's basically big, bright and white.

[00:31:12] And this will be just above the northeastern horizon in the early hours of the morning.

[00:31:17] Mars will be there too, above the northeastern horizon, but not until after about 2.30, when it rises above the horizon.

[00:31:26] So if you're up around that time, you should be able to spot Mars.

[00:31:30] It's got a distinct, ruddy colour.

[00:31:32] A sort of a reddish, ruddy sort of colour, even a bit orangey, which makes it quite easy to identify.

[00:31:37] And it's quite a lot dimmer than Jupiter.

[00:31:40] Well, they're separated quite a lot in the sky in terms of the angle between them as we're looking at them,

[00:31:45] but you should be able to spot the two of them together.

[00:31:47] Jupiter, big and bright, and Mars, lower down, ruddy sort of colour and a little bit dimmer.

[00:31:53] And that's Stuart is the sky for November.

[00:31:56] That's Jonathan Nellie from Sky and Telescope magazine.

[00:31:59] And this is Space Time.

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