Cosmic Supernova Secrets, IO's Volcanic Heartbeat, and New Glenn's Vertical Ascent: S27E147

[00:00:00] This is SpaceTime Series 27 Episode 147 for broadcast on the 6th of December 2024.

[00:00:07] Coming up on SpaceTime, the strange stellar explosion that highlighted the cosmic past,

[00:00:12] how Jovian moon volcanoes may control Io's insides, and America's next mega rocket goes vertical.

[00:00:20] All that and more coming up on SpaceTime.

[00:00:25] Welcome to SpaceTime with Stuart Gary.

[00:00:44] Astronomers have been given a rare peek into the early history of the Universe thanks to a rather unusual supernova event.

[00:00:50] The stellar explosion involved the core collapse of a bloated ancient red supergiant star on the outskirts of a nearby galaxy.

[00:00:58] The unusual supernova, called 2023 UFX, represents the most metal poor stellar explosion ever observed.

[00:01:05] A report in the Astrophysical Journal indicates the host galaxy also has an extremely low level of metallicity.

[00:01:13] Astronomers refer to all elements other than hydrogen and helium as metals.

[00:01:17] The study's lead author, Michael Tucker from Ohio State University, says that since the metals produced within supernovae inform their properties,

[00:01:25] including how stars evolve and die, learning more about their formation can tell astronomers much about the state of the Universe when it began,

[00:01:32] especially since essentially there were no metals around during the time of its birth.

[00:01:37] Tucker says if you want to predict how, say, the Milky Way came to be, you need to have a good idea first of how the first exploding stars seeded the next generation.

[00:01:46] He says understanding that gives astronomers a great example of how those first objects affected their surroundings.

[00:01:53] And this is where dwarf galaxies come in.

[00:01:56] They're especially useful as local analogues, showing the conditions scientists might expect to see in the early Universe.

[00:02:02] Because of them, astronomers know that while the first galaxies were metal poor, all the big bright galaxies near the Milky Way had plenty of time for stars to explode,

[00:02:12] and therefore increase the amount of metal content.

[00:02:14] The amount of metals a supernova has also influences aspects of the number of nuclear reactions it may have, or how long its explosion remains bright.

[00:02:23] It's also one of the reasons that many low mass stars also occasionally run the risk of collapsing into black holes.

[00:02:30] Typically, any metal poor supernova that astronomers would expect to find would likely be too faint to be seen from our galaxy because of how far away they are.

[00:02:39] Now, thanks to instruments like NASA's Webb Space Telescope, detecting distant metal poor galaxies is much easier.

[00:02:45] The observations of 2023 UFX revealed that many of its properties and behaviours are distinctly different from supernovae in nearby galaxies.

[00:02:54] For example, it had a period of brightness that stayed steady for about 20 days before declining.

[00:03:00] On the other hand, the brightness of its metal rich counterparts usually lasts about 100 days.

[00:03:05] The study also showed that a large amount of fast moving material was ejected during the explosion,

[00:03:11] and that suggests it must have been spinning very quickly when it exploded.

[00:03:14] This result implies that rapidly spinning metal poor stars must have been relatively common during the early days of the universe.

[00:03:22] Tucker and colleagues think the supernova likely had weak stellar winds, streams of charged particles emanating from the star's atmosphere,

[00:03:29] and that led it to cultivate and release so much energy.

[00:03:32] Overall, their observations are providing the groundwork for other astronomers to better investigate how metal poor stars survive in different cosmic environments,

[00:03:41] and may even help some theorists more accurately model how supernova behaved in the early universe.

[00:03:47] This is Space Time.

[00:03:49] Still to come, how Jovian Moon volcanoes may help control Io's insides,

[00:03:55] and America's next new mega rocket goes vertical.

[00:03:58] All that and more still to come on Space Time.

[00:04:17] A new study has found that the Jovian Moon Io has active volcanoes at its poles which may help regulate internal tidal heating.

[00:04:26] Io is the most volcanically active world in the solar system.

[00:04:29] It's a place where instead of weather reports, you'd have volcanology reports,

[00:04:33] with say, lava fountains to the north or magma lakes forming in the east.

[00:04:37] By staring into the hellish landscape of Io, astronomers have been able to study a fundamental process in planetary formation and evolution,

[00:04:46] namely that of tidal heating.

[00:04:48] Tidal heating is caused as a body, like say Io for example,

[00:04:51] is constantly being crushed and stretched as it orbits through the massive gravitational field of its host planet Jupiter and other nearby moons.

[00:05:00] All this pushing and pulling causes lots of internal friction, and that causes heating.

[00:05:05] Tidal heating plays an important role in heating and orbital evolution of celestial bodies.

[00:05:11] It provides the warmth necessary to form and sustain subsurface liquid water oceans

[00:05:16] in the moons around some of the gas giants, like Jupiter's Europa and Saturn's Enceladus.

[00:05:22] The study's lead author, Madeline Pettine from Cornell University,

[00:05:26] says that studying the inhospitable landscape of Io's volcanoes even inspires science to look for life.

[00:05:32] By examining flyby data from NASA's Juno spacecraft,

[00:05:36] Pettine and colleagues discovered Io's active polar volcanoes may be helping to regulate tidal heating,

[00:05:42] and it's that heating which causes friction in the moon's magma interior.

[00:05:46] The observations reported in the journal Geophysical Research Letters

[00:05:50] shows that Io has a surprising number of active volcanoes at its poles,

[00:05:54] as opposed to those in the more common equatorial regions.

[00:05:57] In the north, a cluster of four volcanoes,

[00:06:00] Asus, Zaal, Tonatiuh, and one unnamed volcano,

[00:06:04] and an independent one named Loki,

[00:06:06] were all highly active and persistent,

[00:06:08] with a long history of both space-based and ground-based observations.

[00:06:12] A southern group of volcanoes,

[00:06:14] Kan Haliki, Uttar, and Lakioi,

[00:06:17] also demonstrated strong activity.

[00:06:19] The long-lived quartet of northern volcanoes

[00:06:22] was seen to concurrently become bright and seem to respond to one another.

[00:06:25] Pettine says they all got bright and then dimmed again at a comparable pace.

[00:06:30] She says it was fascinating to see these volcanoes acting in unison

[00:06:34] and seeing how they respond to each other.

[00:06:37] This is space-time.

[00:06:39] Still to come, America's next mega-rocket goes vertical,

[00:06:42] and the December solstice,

[00:06:44] the ticking time bomb of Etta Carina,

[00:06:46] and the rock comet Phaeton

[00:06:48] are among the many highlights of the December night skies on Skywatch.

[00:07:08] America's latest mega-rocket, Blue Origin's new Glenn,

[00:07:11] has been hoisted into its vertical position on its launch pad

[00:07:14] in preparation for its hot fire test

[00:07:17] in the lead-up to its maiden flight later this year.

[00:07:20] The 98-metre-tall launch vehicle

[00:07:22] is the latest in a series of massive heavy-lift rockets

[00:07:25] being developed in the United States

[00:07:27] to carry huge payloads into orbit and beyond.

[00:07:30] It'll eventually join NASA's SLS Orion Moon rocket

[00:07:34] and SpaceX's Starship Super Heavy

[00:07:36] in setting new standards for launch capabilities.

[00:07:39] The upcoming hot fire test will allow mission managers

[00:07:42] to test both the rocket itself

[00:07:44] and the launch pad ground systems

[00:07:46] at the newly built Space Launch Complex 36

[00:07:48] at the Cape Canaveral Space Force space in Florida.

[00:07:51] New Glenn, which is named after John Glenn,

[00:07:54] the first American to achieve orbital space flight,

[00:07:56] was carried horizontally from its vehicle assembly building

[00:07:59] to the launch pad

[00:08:00] by a new specially-built 91-metre-long

[00:08:02] 1,000 energy and 14-tonne transport erector vehicle.

[00:08:07] The maiden flight had originally been targeted for last month,

[00:08:09] but it was bumped back to this month

[00:08:11] because of ongoing technical issues.

[00:08:13] The launch is the first of two tests

[00:08:15] needed to get certification by the United States Space Force

[00:08:18] to fly national security missions.

[00:08:20] New Glenn is designed to lift payloads of 45 tonnes

[00:08:23] into low-Earth orbit,

[00:08:25] 13.6 tonnes into geostationary transfer orbit

[00:08:28] and 7 tonnes into translunar orbits.

[00:08:31] Blue Origin plans to land the first stage of New Glenn

[00:08:34] on a floating barge after launch

[00:08:36] for eventual refurbishment and reuse.

[00:08:39] That's similar to how SpaceX lands the first stage

[00:08:41] of its Falcon 9 rockets.

[00:08:43] Blue Origin have been perfecting the manoeuvre

[00:08:45] on their smaller New Shepard rockets

[00:08:47] which are used for space tourism flights out of Texas.

[00:08:49] New Glenn's first stage booster will be powered by

[00:08:52] seven BE-4 engines producing up to 3.9 million pounds of thrust.

[00:08:57] Now this same engine is also being used on the United Launch Alliance's

[00:09:01] new Vulcan Centaur rocket.

[00:09:02] The booster is designed for reuse up to at least 25 times.

[00:09:06] The second stage, which is non-reusable, will be powered by two BE-3 engines.

[00:09:11] They're based on the same engine used aboard New Shepard.

[00:09:14] And a third stage using a single BE-3 engine is now also in development for eventual use on the new rocket.

[00:09:21] This is Space Time.

[00:09:39] Time now to turn our eyes to the skies with December Skywatch.

[00:09:44] December is the 12th and final month of the year in both the Julian and Gregorian calendars.

[00:09:50] December got its name from the Latin word decim meaning 10,

[00:09:53] because it was originally the 10 month of the year in the old Roman calendar which began in March.

[00:09:58] The astronomical highlight of the month is the December solstice,

[00:10:02] which this year occurs at 20-20 Australian Eastern Daylight Time on the evening of Saturday,

[00:10:07] December the 21st.

[00:10:08] That's 4-20 on Saturday morning US Eastern Standard Time and 9-20 in the morning Greenwich Mean Time.

[00:10:15] This is when the sun appears to reach the zenith directly over the Tropic of Capricorn.

[00:10:20] In the United States, in the Northern Hemisphere, it marks the winter solstice, signifying the first day of winter.

[00:10:26] But the good news is that from now on, the days start to get longer again.

[00:10:31] On the other hand, south of the equator, summer has well and truly arrived,

[00:10:34] and the days are usually at their warmest.

[00:10:37] Earth's seasons occur because of the tilt of the planet's spin axis,

[00:10:41] which is inclined at 23.4 degrees in relation to the sun.

[00:10:44] Now generally speaking, Earth's axis always points to the same position in space,

[00:10:49] regardless of the position of the Earth as it orbits around the sun.

[00:10:53] So on the day of the December solstice,

[00:10:55] the Earth's south pole is tilted towards the sun,

[00:10:57] so its southern hemisphere gets more daylight and more direct sunlight.

[00:11:01] So it's hotter, and its southern hemisphere is in summer.

[00:11:04] Six months later, during the June solstice,

[00:11:07] the north pole is tilted towards the sun,

[00:11:09] and so it's the northern hemisphere which experiences summer,

[00:11:11] or the southern hemisphere gets less daylight, longer nights,

[00:11:14] and the sunlight strikes the surface of the planet at a shallower angle,

[00:11:18] meaning less heat, and so the southern hemisphere is in winter.

[00:11:21] In between these two, we have the March and September equinox.

[00:11:25] That's when the northern and southern hemispheres get roughly equal amounts of daylight and heat,

[00:11:29] giving us the seasons of spring and autumn.

[00:11:32] Now earlier, we said that generally speaking,

[00:11:35] Earth's axis always points to the same position in space,

[00:11:38] regardless of Earth's orbital position around the sun.

[00:11:40] And while that's true in our day-to-day lives,

[00:11:43] over geologic time, approximately 25,772 years,

[00:11:48] a gravity-induced effect known as axial precession causes a slow and continuous change

[00:11:53] in the orientation of Earth's rotational axis.

[00:11:56] You can see the same effect in the precession of a spinning top

[00:12:00] as its axis traces out a pair of cones joined by the aspices.

[00:12:03] Earth's precession was historically called the precession of the equinoxes

[00:12:07] because the equinoxes moved westwards along the ecliptic relative to the fixed background stars.

[00:12:13] This slow precession of the Earth's axis means that over 25,772 years,

[00:12:19] the positions of the south and north celestial poles

[00:12:22] appears to move in circles against the space-fixed background stars.

[00:12:26] So, while today the star Polaris lies approximately at the north celestial pole,

[00:12:31] this will change over time.

[00:12:33] And Gamma Cephi will ultimately become the north star in about 3,200 years from now.

[00:12:38] It also means the seasons would slowly move through different calendar months,

[00:12:43] but we make adjustments to the calendar to compensate for that.

[00:12:46] In most parts of the world, the seasons begin on the day of the solstice or equinox.

[00:12:51] However, Australia's a bit different. We're a bit strange.

[00:12:54] Instead, here, seasons start on the first day of a particular calendar month.

[00:12:59] That means the 1st of March for autumn, 1st of June for winter,

[00:13:03] the 1st of September for spring and December the 1st for summer.

[00:13:07] Because of the relatively small amount of elongation in Earth's orbit around the Sun,

[00:13:11] Earth's seasons are determined by its axial tilt rather than orbital distance.

[00:13:15] Currently, Earth's closest orbital position to the Sun, known as perihelion,

[00:13:19] occurs about two weeks after the December solstice.

[00:13:22] And it's furthest from the Sun, known as aphelion, about two weeks after the June solstice.

[00:13:27] Now that means the next perihelion will occur at 12.28am on the morning of Sunday, January 5th,

[00:13:34] 2025 Australian Eastern Daylight Time, when planet Earth will be 147,103,686 km from the Sun.

[00:13:43] That's at 8.28am on the morning of Saturday, January 4th, US Eastern Standard Time,

[00:13:49] and 1.28 in the afternoon, Greenwich Mean Time.

[00:13:52] Like axial precession, Earth's orbit also changes gradually over geologic time,

[00:13:57] getting more or less elongated and changing perihelion and aphelion.

[00:14:01] Even the degree of the tilt of Earth's axis changes over thousands of years.

[00:14:05] Now collectively, all these changes are known as Milankovic cycles,

[00:14:10] after the Serbian geophysicist and astronomer Milutin Milankovic,

[00:14:14] who in the 1920s hypothesized that variations in eccentricity, axial tilt and precession,

[00:14:19] resulted in cyclic variations in solar radiation reaching the Earth,

[00:14:23] and that this orbital forcing strongly influenced Earth's climatic patterns.

[00:14:29] Okay, let's start our tour of the December night skies in the west,

[00:14:33] where midway up from the horizon is Fulmaholt,

[00:14:35] the brightest star in the constellation Pisces austrinus, the southern fish.

[00:14:40] Fulmaholt is a very young white spectral type A main sequence star,

[00:14:44] about 1.8 times that diameter of the Sun,

[00:14:46] and located reasonably nearby, just 25 light years away.

[00:14:50] Now, main sequence stars are those undergoing hydrogen fusion into helium in their cores.

[00:14:57] Astronomers describe stars in terms of spectral types,

[00:15:00] a classification system based on temperature and characteristics.

[00:15:03] The hottest, most massive and most luminous stars are known as

[00:15:07] spectral type O blue stars.

[00:15:09] They're followed by spectral type B blue white stars,

[00:15:12] then spectral type A white stars,

[00:15:15] spectral type F whiteish yellow stars,

[00:15:17] spectral type G yellow stars,

[00:15:19] that's where our Sun fits in by the way.

[00:15:21] Then comes spectral type K orange stars,

[00:15:24] and the coolest and least massive known stars,

[00:15:26] are spectral type M red stars.

[00:15:29] Now, each spectral classification can also be subdivided using a numeric digit,

[00:15:34] which represents temperature,

[00:15:35] with zero being the hottest and nine the coolest,

[00:15:37] and a Roman numeral to represent luminosity.

[00:15:40] So, our Sun is a G2V or G25 yellow dwarf star.

[00:15:45] Also included in the stellar classification system are spectral types L, T and Y,

[00:15:50] which are assigned to failed stars known as brown dwarves,

[00:15:54] some of which were actually born as spectral type M red dwarf stars,

[00:15:57] but became brown dwarves after losing some of their mass.

[00:16:01] Brown dwarves fit into a unique category between the largest planets,

[00:16:05] which are about 13 times the mass of Jupiter,

[00:16:07] and the smallest spectral type M red dwarf stars,

[00:16:10] which are about 75 to 80 times the mass of Jupiter,

[00:16:13] or roughly 0.08 solar masses.

[00:16:17] In 2008, astronomers detected planets orbiting around Formalholt.

[00:16:21] At this stage, it's not known if anyone was looking back.

[00:16:24] 5,000 years ago, the ancient Mesopotamians used Formalholt

[00:16:28] to mark the Northern Hemisphere's winter solstice.

[00:16:31] Now, turning to the left of Formalholt is Achenar or Alpha Erydney,

[00:16:35] the brightest star in the constellation Erydnus, the river.

[00:16:38] Located 139 light-years away, Achenar has 7 times the diameter of the Sun,

[00:16:43] and rotates some 15 times faster, giving it a very obvious oblate shape.

[00:16:48] The effect of this rapid rotation is that the star flattens at its poles,

[00:16:53] but bulges in the middle.

[00:16:54] In fact, its equatorial diameter is about 50% greater than its polar diameter.

[00:16:59] It turns out Achenar is actually part of a multiple-star system,

[00:17:03] Alpha Erydney A and Alpha Erydney B.

[00:17:05] The primary star, Alpha Erydney A, is a hot blue spectrotype B main sequence star.

[00:17:11] Its smaller companion, Alpha Erydney B, is a spectrotype A white star.

[00:17:16] Their pair orbit each other around a common centre of gravity

[00:17:19] at a distance of about 12 astronomical units.

[00:17:21] An astronomical unit is the average distance between the Earth and the Sun,

[00:17:26] about 150 million kilometres or 8.3 light minutes.

[00:17:30] Moving further left from Achenar and just above the horizon

[00:17:33] is Canopus, the brightest star in the southern constellation of Corrine of the Keel.

[00:17:38] And it's also the second brightest star in the night sky after Sirius.

[00:17:42] Canopus is a white giant star nearing the end of its life.

[00:17:46] It's located about 310 light-years away.

[00:17:49] It has about 8.5 times the mass of the Sun,

[00:17:51] but it's expanded out to about 71 times the Sun's diameter.

[00:17:55] Canopus has some 1300 times the brightness of the Sun,

[00:17:59] and in fact, it's the brightest star within 700 light-years of Earth.

[00:18:03] Its name originates in mythology from the time of the Trojan Wars,

[00:18:07] and the navigator for Menelaus, the King of Sparta.

[00:18:11] Located between Canopus and the Southern Cross in Corrine,

[00:18:14] known in the Trumpler-16 open star cluster,

[00:18:16] is the ticking time bomb that is Etta Corrina,

[00:18:19] a pair of huge blue stars undergoing the final violent phase of their existence

[00:18:24] for exploding its massive core-collapse supernovae.

[00:18:27] The binary system is located some 7,500 light-years away,

[00:18:32] buried deep within the great nebula of Corrina,

[00:18:34] a massive cloud of gas and dust stretching some 6.5 to 10,000 light-years away.

[00:18:40] A light-year is about 10 trillion kilometers.

[00:18:43] The distance a photon can travel in an Earth-year at 300,000 kilometers per second,

[00:18:48] the speed of light in a vacuum, and the ultimate speed limit of the universe.

[00:18:52] The stars in Etta Corrina are classified as highly luminous spectrotype O blue hypergiants.

[00:18:58] The primary star is estimated to be around 150 to 200 times the mass of our Sun,

[00:19:04] with some 5 million times the Sun's luminosity, 800 times its radius,

[00:19:08] and a surface temperature of up to 32,500 Kelvin.

[00:19:12] The primary star in this binary pair is also the only known star to produce ultraviolet laser emissions.

[00:19:18] The companion star, although smaller than the primary, just 80 solar masses and 20 times the Sun's radius,

[00:19:25] is even hotter, with surface temperatures of around 37,200 Kelvin.

[00:19:29] The two stars orbit each other every 5.54 Earth years,

[00:19:33] cocooned in a gigantic twin-lobed cloud of gas and dust known as the Homunculus Nebula,

[00:19:39] a bipolar emission and reflection nebula.

[00:19:41] The primary star in this binary pair has lost about 30 solar masses in recent times.

[00:19:47] Both Etta Corrina and its surrounding shroud of dust generate huge amounts of infrared radiation,

[00:19:53] making it the brightest infrared source in the sky.

[00:19:56] Etta Corrina experiences tremendous outbursts.

[00:19:59] During one event, it became almost as bright as the star Sirius.

[00:20:04] Known as the Great Eruption, it began in 1837 and reached its peak in 1843,

[00:20:10] when it was one of the brightest objects in the night sky,

[00:20:13] before gradually fading away again by 1856.

[00:20:17] Etta Corrina underwent another, slightly smaller eruption in 1892,

[00:20:21] and has again been steadily brightening since about 1940.

[00:20:25] Both these stars are now nearing the end of their lives in the main sequence,

[00:20:29] and they're expected to go supernova in an astronomically short space of time.

[00:20:33] When they do go supernova, Etta Corrina will be visible in the daylight skies even here on Earth.

[00:20:39] In fact, they could become brighter than the full moon for months on end.

[00:20:42] No one knows exactly when Etta Corrina will go supernova.

[00:20:46] A single star, a star originally around 150 times as massive as the Sun,

[00:20:51] would typically reach core collapse as it will fray it within about 3 million years.

[00:20:56] At low metallicity, many massive stars will collapse directly to form stellar mass black holes,

[00:21:01] with no visible explosion, or possibly a sub-luminous supernova.

[00:21:05] And a small fraction will produce apparent stability supernova.

[00:21:08] But at solar metallicity and above, there's expected to be sufficient mass loss before collapse

[00:21:14] to allow a visible supernova to appear.

[00:21:17] Now if there's still a large amount of expelled material close to the star,

[00:21:21] the shock wave formed by the supernova explosion impacting on the circumstellar material

[00:21:25] could effectively convert the kinetic energy into radiation,

[00:21:28] resulting in a superluminous supernova or hypernova,

[00:21:32] several times more luminous than a typical core-collapse supernova and much longer lasting.

[00:21:36] Highly massive progenitors may also eject sufficient nickel to cause a superluminous supernova

[00:21:42] simply from the radioactive decay.

[00:21:44] Now the resulting remnant would then form a black hole,

[00:21:47] since it's highly unlikely that such a massive star could ever lose enough mass from its core

[00:21:52] not to exceed the limit for a neutron star, about 2.3 or 2.4 solar masses.

[00:21:58] But the existence of a massive companion star brings many other possibilities into play.

[00:22:03] If Eta-Corena ray was rapidly stripped of its outer layers,

[00:22:07] it might become a less massive WC or WO type star when core collapse is finally reached.

[00:22:12] This would result in a Type 1b or Type 1c supernova due to the lack of hydrogen and possibly helium.

[00:22:19] And these supernovae are thought to be possible progenitors for some types of gamma ray bursts.

[00:22:24] Now, a typical core-collapse supernova at the distance of Eta-Corena would look as bright as the planet Venus,

[00:22:30] the third brightest object in the sky after the Sun and Moon.

[00:22:33] On the other hand, a superluminous supernova could be five magnitudes brighter,

[00:22:37] possibly the brightest supernova in recorded history.

[00:22:40] But I'm pleased to say that based on our current data,

[00:22:44] Eta-Corena is not expected to produce a gamma ray burst,

[00:22:46] and its axis isn't currently aimed anywhere near the Earth.

[00:22:50] And at 7,500 light-years away,

[00:22:52] the star is unlikely to directly affect terrestrial life forms on Earth

[00:22:56] thanks to our planet's atmosphere and magnetosphere.

[00:22:58] But the ozone layer of the planet could be damaged,

[00:23:02] as would orbiting spacecraft and any astronauts in space at the time.

[00:23:05] At least one paper has projected that a complete loss of the Earth's ozone layer

[00:23:09] is a plausible consequence.

[00:23:11] And that would result in a significant increase in ultraviolet radiation

[00:23:15] reaching the planet's surface from the Sun.

[00:23:17] But that would require a typical supernova to be closer than 50 light-years from Earth.

[00:23:22] And even a potential hypernova would still need to be closer than where Eta-Corena is now.

[00:23:27] Another analysis of the possible impact of a supernova in Eta-Corena

[00:23:31] discusses more subtle effects from the unusual illumination,

[00:23:34] such as possible melatonin suppression,

[00:23:37] resulting in insomnia and increased risk of cancer and depression.

[00:23:41] Okay, on that note, let's turn to the east.

[00:23:44] And looking just above the horizon

[00:23:46] is the star that outshines Canopus

[00:23:48] to take the title of the brightest star in the night sky,

[00:23:51] namely Sirius the Dog Star.

[00:23:53] And next to it, in the east-northeastern skies just above the horizon,

[00:23:57] is the constellation of Orion the Hunter.

[00:24:00] There you'll see a very bright red star.

[00:24:02] It's a red supergiant called Betelgeuse,

[00:24:04] better known to most people these days as Betelgeuse.

[00:24:07] Don't say it three times.

[00:24:08] In ancient times, before centuries of mispronunciation,

[00:24:12] its name actually started out as Ibn Yauza.

[00:24:15] Betelgeuse is one of the largest and most luminous stars visible with the unaided eye.

[00:24:20] Located some 430 light years away,

[00:24:22] this bloated old red giant is reaching the end of its life.

[00:24:26] It's truly massive, some 1,100 times the diameter

[00:24:30] and 100,000 times the brightness of our sun.

[00:24:33] Like Etta Carina, Betelgeuse is destined to explode as a core-collapse supernova sometime in the near future.

[00:24:40] Betelgeuse marks the right shoulder of Orion the Hunter,

[00:24:43] although it's all upside down from our perspective here in the Southern Hemisphere.

[00:24:47] That's because Orion was a hunter in Greek mythology,

[00:24:49] so the constellation was viewed from the Northern Hemisphere.

[00:24:52] The earliest known depiction of the Orion constellation was on a prehistoric mammoth ivory carving

[00:24:58] found in a cave in the Arch Valley in West Germany.

[00:25:01] That was in 1979.

[00:25:03] Archaeologists estimate that it had been fashioned between 32,000 and 38,000 years ago.

[00:25:09] The distinctive pattern of Orion has been recognized in numerous cultures around the world,

[00:25:13] including the ancient Babylonian star catalogues dating back to the Late Bronze Age.

[00:25:18] In Greek mythology, Orion was a gigantic, supernaturally strong hunter of ancient times.

[00:25:24] He was the son of Gorgon and Poseidon, also known as Neptune,

[00:25:28] the god of the sea in the Greco-Roman tradition.

[00:25:30] But the goddess Guy became angry at Orion after he boasted that he would kill every animal on Earth.

[00:25:37] So she sent a scorpion to sting Orion to death.

[00:25:40] However, Ophiuchus the serpent bearer revived Orion with an antidote.

[00:25:44] And this is given to be the reason why the constellation Scorpius chases Orion across the sky,

[00:25:50] with the constellation Ophiuchus standing midway between them.

[00:25:54] The other major stars in Orion include Rigel, Orion's left foot, a blue supergiant.

[00:25:59] Having exhausted its core hydrogen, Rigel has swollen out to between 79 and 115 times the sun's radius.

[00:26:06] It's currently fusing heavier and heavier elements at its core,

[00:26:10] meaning it too will soon likely go supernova and collapse to form a neutron star.

[00:26:15] Rigel's estimated to be somewhere between 120,000 and 279,000 times the luminosity of the sun.

[00:26:22] It's a binary system, located 860 light-years away.

[00:26:26] And it has a companion star, Rigel B, some 500 times fainter than the supergiant Rigel A,

[00:26:33] and visible only through a telescope.

[00:26:35] Rigel B itself is a spectroscopic binary system, comprising two main-sequence blue-white stars.

[00:26:42] Spectroscopic binaries are double star systems orbiting each other in such a way

[00:26:46] that they can only be visually separated from our vantage point here on Earth

[00:26:49] by their different spectroscopic signatures.

[00:26:51] The two stars making up Rigel B are estimated to have 3.9 and 2.9 times the mass of the sun respectively.

[00:26:59] And one of these stars, Rigel BB, may itself also be a binary system.

[00:27:04] Rigel B also appears to have a very close visual companion of Rigel C, almost identical in appearance.

[00:27:11] The third brightest star in Orion is Bellatrix, Orion's left shoulder.

[00:27:15] It's a spectrotype B main-sequence blue star, with about 8.6 times the mass and 6 times the radius of the sun.

[00:27:23] Bellatrix is about 250 light-years away.

[00:27:26] It has an estimated age of about 25 million years.

[00:27:30] That's old enough for a star of this mass to start consuming hydrogen in its core

[00:27:34] and begin to evolve away from the main sequence and turn into a blue giant.

[00:27:39] Now, if you look at the three stars which make up Orion's belt,

[00:27:43] you'll see another three stars which make up Orion's sword hanging from the belt.

[00:27:47] And again, that's hanging upwards for those of the Southern Hemisphere.

[00:27:50] And if you look carefully at the middle star, you'll notice it's a bit fuzzy looking.

[00:27:55] That's because it's not a star, but the great nebula of Orion, Messier 42.

[00:28:00] Located just 1,344 light-years away, Messier 42 is the nearest massive star-forming region to Earth.

[00:28:08] Its nebula is estimated to be some 24 light-years across, and it has the mass of more than 2,000 suns.

[00:28:15] The Orion Nebula is one of the most scrutinised and photographed objects in the night sky,

[00:28:20] and it's among the most intensely studied celestial features.

[00:28:23] The nebula has revealed much about the process of how stars and planetary systems

[00:28:28] are formed from collapsing molecular gas and dust clouds.

[00:28:32] By studying M42, astronomers have directly observed protoplanetary disks,

[00:28:37] brown dwarfs, intense and turbulent motions of gas,

[00:28:40] and the photoionising effects of massive nearby stars in the nebula.

[00:28:44] The Orion Nebula contains a very young open cluster known as the Trapezium

[00:28:48] due to the asterism of its four primary stars.

[00:28:51] Now the Trapezium itself is a component of the much larger Orion Nebula cluster,

[00:28:56] an association of about 2,800 stars, all within a diameter of just 20 light-years.

[00:29:02] One of the most stunning nebulas in the constellation Orion is the spectacular

[00:29:07] Horsehead Nebula, Barnard 33.

[00:29:10] The Horsehead is a dark nebula, located just to the south of the star Alnatac,

[00:29:14] which is the furthest east on Orion's belt, and is part of the much larger Orion Molecular Cloud Complex.

[00:29:21] Located around 1,500 light-years away, the Horsehead Nebula was first recorded in 1888.

[00:29:26] It's one of the most identifiable nebulas in astronomy.

[00:29:30] That's because of the shape of its swirling clouds of dark dust and gases,

[00:29:34] which bear an amazing resemblance to a horse's head when viewed from Earth.

[00:29:39] One of the astronomical highlights of the December night skies

[00:29:42] is the annual Geminids meteor shower, which usually peaks around December 13 and 14.

[00:29:48] Radiating out from the direction of the constellation Gemini,

[00:29:51] the Geminids are unusual in that they're not generated by a comet as most other meteor showers are,

[00:29:56] but are produced by the debris trail left behind by the asteroid 3200 Phaeton.

[00:30:01] That makes the Geminids, together with the Quadrantids,

[00:30:04] the only major meteor showers not originating from a comet.

[00:30:08] 3200 Phaeton is highly unusual.

[00:30:11] Its high orbital eccentricity more closely resembles that of a comet than an asteroid.

[00:30:16] And in fact it's speculated that it may be an asteroid

[00:30:19] that simply ran out of all the volatile gases that normally characterize a comet.

[00:30:23] Phaeton's orbit crosses all the inner terrestrial planets,

[00:30:26] Mercury, Venus, Earth and Mars.

[00:30:28] And because it does come relatively close to the Earth,

[00:30:31] this 5km wide space rock is classified as potentially hazardous.

[00:30:36] Phaeton will make its closest approach to Earth on December 14, 2093.

[00:30:41] But at that time it will still pass a relatively comfortable 2,960,000 km away from our planet.

[00:30:47] Interestingly, Phaeton's named after the son of the Greek sun God Helios.

[00:30:51] Legend has it that Phaeton almost destroyed the Earth

[00:30:55] by stealing Helios' chariot and scorching the Earth with the sun,

[00:30:58] almost causing the apocalypse.

[00:31:00] Phaeton approaches the sun closer than any other named asteroid,

[00:31:04] with a perihelion of less than 21 million km,

[00:31:07] that's less than half of Mercury's perihelion distance.

[00:31:10] Coming so close to the sun causes the asteroid's surface to reach over 750 degrees Celsius.

[00:31:17] Observations by NASA's Stereo spacecraft saw dust trails radiating off its surface.

[00:31:22] And in 2010, Phaeton was detected actually ejecting dust into space.

[00:31:28] Astronomers think the intense heat generated by its close approaches to the sun

[00:31:31] causes fractures in the gravel and rocks on the asteroid's surface,

[00:31:35] similar to mud cracks in a dry lake bed.

[00:31:37] And Phaeton's composition also fits the notion of a cometary origin.

[00:31:42] It's classified as a Type B asteroid because it's composed of primarily dark material.

[00:31:47] Type B asteroids are thought to be primitive,

[00:31:50] volatile-rich elements of the early solar system.

[00:31:53] Its composition, orbit and dust trail,

[00:31:55] have led astronomers to refer to Phaeton as a rock comet.

[00:31:58] The Geminids meteors have a yellowish hue,

[00:32:01] and they tend to be a bit larger and more solid than typical meteors from comets.

[00:32:06] Think of grains and rocks rather than dust particles.

[00:32:09] They also move more slowly,

[00:32:11] travelling at about 35 km per second compared to some cometary meteor showers

[00:32:15] which travel at speeds of up to 72 km a second.

[00:32:19] Interestingly, the Geminids are also thought to be intensifying every year,

[00:32:22] with recent showers seeing up to 160 meteors per hour under optimal conditions.

[00:32:27] In the Northern Hemisphere, expect to see up to 120 meteors per hour between midnight and 4am,

[00:32:33] but only from a dark sky.

[00:32:35] Well north of the equator, the radiant rises about sunset,

[00:32:38] reaching a usable elevation from local evening hours onwards.

[00:32:42] In the Southern Hemisphere, the Geminids aren't nearly as spectacular.

[00:32:46] You won't see as many, perhaps just 10 to 20 an hour.

[00:32:49] That's because the radiant doesn't rise above the horizon at all.

[00:32:52] Now for listeners in the Northern Hemisphere,

[00:32:54] there's a second meteor shower in December.

[00:32:56] The Ursiads, which radiate out from the direction of Ursa Minor, the Little Dipper.

[00:33:00] The Ursiads are generated by debris left behind by the comet 8P-Tuttle.

[00:33:05] They're a compact stream, peaking during the night of December 22nd

[00:33:09] and the early morning hours of December 23rd.

[00:33:12] If you look towards the bowl of the Little Dipper,

[00:33:14] you might see about 10 meteors an hour.

[00:33:16] And now with the rest of the December night skies,

[00:33:19] we're joined by Jonathan Nally from Sky and Telescope magazine.

[00:33:22] G'day Stuart.

[00:33:23] Yeah, well it is December, which means it's summertime where I live.

[00:33:26] If you're north of the equator, you're entering winter instead, of course.

[00:33:28] But where I am down here, it's very hot at the moment.

[00:33:30] It's going to get even hotter.

[00:33:31] The thing is with summertime viewing it, you get fewer hours of nighttime, of course,

[00:33:34] because the daylight's longer, so night hours are shorter.

[00:33:37] But at least the weather's good.

[00:33:38] You don't have to go out in freezing cold temperatures.

[00:33:40] Look, we normally start our Sky Tour in the south,

[00:33:42] but this time we'll start with the sky to the east for this time of the year.

[00:33:46] So once the sun has gone down and the sky is dark,

[00:33:48] you look to the east and you will see the mighty constellation Orion the Hunter

[00:33:53] sitting above the eastern horizon.

[00:33:54] It's pretty easy to make out because there's a little trio of stars in a row,

[00:33:58] this little straight line of these three stars quite close together.

[00:34:01] That's known as the Hunter's Belt, Orion the Hunter's Belt.

[00:34:03] And it's quite easy to see, as are two of Orion's brightest stars.

[00:34:08] You've got bluish Rigel, which is above the belt,

[00:34:10] as you look at it in the eastern sky,

[00:34:12] and you've got reddish Betelgeuse, which is down below the belt.

[00:34:15] So they're down quite low towards the horizon about 9 o'clock, 9.30 or so,

[00:34:19] but it rises higher as the night goes on,

[00:34:22] so you won't have any trouble finding it.

[00:34:23] These two stars, Rigel and Betelgeuse,

[00:34:25] so Rigel is the seventh brightest star in the night sky,

[00:34:27] and Betelgeuse is the tenth.

[00:34:29] So they are pretty bright.

[00:34:30] Rigel is big and bright literally.

[00:34:31] It's more than 70 times wider than our sun, and it's 120,000 times as bright.

[00:34:38] But thankfully, it's more than 850 light years from us,

[00:34:40] otherwise you'd be in real trouble.

[00:34:42] Some of these stars out there, they're just enormous,

[00:34:44] and they're very intrinsically bright,

[00:34:45] but they're so far away that they just look like stars.

[00:34:48] If they were closer in, we'd have sort of permanent daylight.

[00:34:51] We'd have our star giving us daylight during the day,

[00:34:54] and night time, if some of these bright stars are much closer,

[00:34:57] then you'd be able to read by them.

[00:34:58] There'd be so much light.

[00:34:59] Betelgeuse, the other star, is even bigger.

[00:35:00] It's around 700 times wider than our sun, and it's more than 70,000 times as bright.

[00:35:06] So a couple of really giant stars you've got there.

[00:35:08] Incidentally, I mentioned the sun there in daylight.

[00:35:10] You do know, don't you, Stuart, that it has been scientifically proven

[00:35:14] that the moon is better than the sun?

[00:35:16] Have you heard this?

[00:35:16] Okay, why is the moon better than the sun?

[00:35:18] Well, see, the moon shines at night when everything's dark, and it gives us light by which to see things,

[00:35:25] you know, so we can get around at night time.

[00:35:27] But the sun, well, it only shines during the daytime, and it's light anyway.

[00:35:31] What about a new moon?

[00:35:32] You wish I hadn't asked you that.

[00:35:36] That was George Gamow.

[00:35:38] It was a George Gamow joke, that was.

[00:35:40] His name's George Gamow, the famous astronomer Gamow.

[00:35:43] He was the one who said, if we ever go to the sun, we shouldn't go at night time when it's cooler.

[00:35:46] That's right.

[00:35:47] Now listen, talking about those stars in Orion, if you start at Orion and you go to the left,

[00:35:51] as you're looking at it in the night sky, which actually means you're going north,

[00:35:54] if you're looking further to the north, you should see a reddish star that makes up one corner of a triangle

[00:35:59] or a wedge of stars pointing up from the horizon.

[00:36:02] Now that star is called Albeirond, and the triangle is a star cluster called the Hyades,

[00:36:06] and they're both part of the constellation of Taurus.

[00:36:09] Now if you can get a pair of binoculars, just binoculars, you don't need a telescope,

[00:36:11] just get a pair of binoculars onto that wedge-shaped cluster of stars,

[00:36:14] please do so because it's really, really pretty.

[00:36:17] Binoculars give you just that little bit of extra light-gathering power to see fainter things,

[00:36:21] as do telescopes, of course, but it's just binoculars that on their own,

[00:36:24] you'll see more and more stars than just the little wedge shape that you can see

[00:36:28] of probably about half a dozen, seven or eight stars or so in the Hyades.

[00:36:31] Get some binoculars onto it and you'll see a few dozen.

[00:36:34] And a bit further to the left of the Hyades is another star cluster that we've spoken before about on the program,

[00:36:39] and it's even prettier, and this is the Pleiades, which is also known as the Seven Shifters

[00:36:43] because it's long been said that most people can see seven stars out of the thousand or so that are in this cluster,

[00:36:49] but all those other ones are far too faint for the unaided eye.

[00:36:52] You need to telescope the star and bring those out.

[00:36:54] And it's interesting because it's been given that name Seven Sisters or something similar

[00:36:58] in many different cultures scattered all across the globe and dating from a long, long time ago.

[00:37:02] And it's been suggested actually that the idea of these little bit of stars being seven sisters,

[00:37:07] some sort of mythology associated with seven sisters in the sky, that idea originated tens of thousands of years ago

[00:37:14] and spread around the world as early humans made their way across the planet.

[00:37:18] And if this is correct, it's probably the oldest mythology for our entire species that has survived to the present day.

[00:37:24] We're talking, you know, tens of thousands of years, a long, long time back.

[00:37:28] The other interesting thing about this is that even though the stars are called the Seven Sisters,

[00:37:32] most people with average eyesight and dark skies can only see six.

[00:37:36] And it's been that way for a long, long time.

[00:37:38] And so it's been suggested that maybe there was a seventh star that used to be brighter a long time ago

[00:37:45] and has now faded away.

[00:37:46] The star will still be there, but stars do change in their brightness.

[00:37:50] So maybe there was a seventh one that was brighter a long time ago.

[00:37:53] Or maybe there were two stars that are now close together, further apart in the distant past.

[00:37:59] And so you could see them separately as two stars.

[00:38:01] So you made up a total of seven.

[00:38:02] Whereas now, you know, we see six.

[00:38:05] So it's a bit of a mystery still, that one.

[00:38:06] But it really is interesting how different cultures around, not all cultures,

[00:38:09] some cultures have other ideas, other mythologies associated with this little group of stars.

[00:38:13] But so many of them do associate them with a group of sisters.

[00:38:17] Seven sisters or seven women.

[00:38:19] It always seems to be like that.

[00:38:20] And in some of these cultures, they're also being chased by Orion the hunter.

[00:38:24] That's right.

[00:38:25] He's chasing them.

[00:38:26] This includes Aboriginal cultures in Australia.

[00:38:28] It's amazing.

[00:38:28] Very common story.

[00:38:29] So it's not impossible that there was a common origin going back tens of thousands of years from somewhere.

[00:38:35] And that story just traveled.

[00:38:37] Because back in those days, before writing and everything, it was verbal and mythologies were passed along.

[00:38:42] So it's interesting that could be the old surviving mythology.

[00:38:45] Now, turning to the south, we haven't mentioned the south yet.

[00:38:48] If you look down to the south, we'll see that the Southern Cross, well, you might see the Southern Cross upside down.

[00:38:52] But for many people, it's below the horizon, sort of mid-evening this time of the year.

[00:38:56] Certainly for the people in the northern hemisphere, but even people in the southern hemisphere, I mean, I can't see it about 9 o'clock at night where I live.

[00:39:02] Those at latitudes of around 40 degrees south or further will see the Cross just above the southern horizon.

[00:39:08] But as the Earth turns, the Cross will sort of rise in the southeast.

[00:39:13] So if you give it a few hours, get to midnight or past midnight or so, particularly after midnight this time of year,

[00:39:18] you will see the Southern Cross starting to come up again in the southeast.

[00:39:21] It will be lying on its left-hand side, but the Earth has turned a bit more on its axis.

[00:39:24] Also in the south, but only if you have dark skies, the two things you really shouldn't miss, and that's the two nearest sizable galaxies to our own.

[00:39:32] These are known as the large and small Magellanic Cloud.

[00:39:34] You'll find them about halfway up from the southern horizon, and they do just look like faint fuzzy clouds, but they are in fact galaxies full of millions of stars.

[00:39:41] To a naked eye, you're not going to see any of those individual stars.

[00:39:44] It just looks like a milky patch.

[00:39:45] But if you have a telescope or know someone who's got a telescope, then get a telescope onto them and you will start to see more detail.

[00:39:52] They're including some fantastic nebulae and star-bust images.

[00:39:55] There's quite a lot.

[00:39:56] These two galaxies, astronomers are very fond of them because it gives us an opportunity to study things in other galaxies, but most galaxies are very far away.

[00:40:05] These two are close, so it gives us a bit more of a close-up view of how things are in other galaxies.

[00:40:09] Now let's have a look at which planets we can see in the evening.

[00:40:11] There's three of them.

[00:40:12] Venus is the obvious one.

[00:40:14] It's shining big and bright above the western horizon after sunset.

[00:40:17] You really can't miss it.

[00:40:18] It's really big and bright.

[00:40:19] On the opposite side of the sky, just above the western horizon, and near that Paiades star cluster I mentioned earlier, is Jupiter.

[00:40:25] It's not quite as bright as Venus, but it's still prominent.

[00:40:28] It has a slightly sort of off-white tinge to it.

[00:40:31] Probably to say, you wouldn't call it red or yellow.

[00:40:35] Beige, beige sort of.

[00:40:36] Yeah, beige-y sort of.

[00:40:38] Maybe even a slight pinkish tinge, but only the tiniest amount.

[00:40:42] When it's down low on the horizon, you get the murk of our atmosphere changes the colours and things.

[00:40:47] So wait until Jupiter is risen up higher above the horizon.

[00:40:50] It's out of the murk of the pollution and dust and everything down in the lower part of the atmosphere.

[00:40:55] And then you'll see that it looks just slightly off-white.

[00:40:57] And very high in the northwest in the evening at the moment is Saturn.

[00:41:01] Now it's thinner than Venus and Jupiter.

[00:41:04] It's not quite as bright.

[00:41:05] In fact, it's nowhere near as bright.

[00:41:06] But it does have a telltale yellowish colour.

[00:41:08] You really can't miss it.

[00:41:09] And if you do have access to a small telescope, even if it's a tiny one, even a small telescope,

[00:41:13] take a look, or you should be able to see the planet's wings.

[00:41:16] And Saturn in its wings always looks great to a telescope.

[00:41:18] And Stuart, that's the start of December.

[00:41:20] That's Jonathan Nally from Sky & Telescope magazine.

[00:41:23] And this is Space Time.

[00:41:26] And that's the show for now.

[00:41:43] Space Time is available every Monday, Wednesday and Friday through Apple Podcasts, iTunes, Stitcher,

[00:41:49] Google Podcasts, Pocket Casts, Spotify, Acast, Amazon Music, Bytes.com, SoundCloud, YouTube,

[00:41:57] your favourite podcast download provider, and from SpacetimeWithStewartGary.com.

[00:42:03] Space Time is also broadcast through the National Science Foundation on Science Zone Radio

[00:42:07] and on both iHeartRadio and TuneIn Radio.

[00:42:11] And you can help to support our show by visiting the Space Time store

[00:42:14] for a range of promotional merchandising goodies.

[00:42:17] Or by becoming a Space Time patron,

[00:42:20] which gives you access to triple episode commercial free versions of the show,

[00:42:23] as well as lots of bonus audio content which doesn't go to air,

[00:42:27] access to our exclusive Facebook group and other rewards.

[00:42:30] Just go to SpacetimeWithStewartGary.com for full details.

[00:42:35] You've been listening to Space Time with Stuart Gary.

[00:42:38] This has been another quality podcast production from Bytes.com.