December 2024
The Sky Tonight - December 2024
December takes us into the season of Birak and brings with it the unwelcomely hot weather for the next few months. Fittingly, …
ExploreNew Moon
December 4
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The casual observer
The bright centre of the Milky Way is mostly below the western horizon by now, which means all the good stuff is in the east during the evenings. The relative position of the Earth and Sun mean that we are facing away from the centre of the Milky Way and now seeing the outer arm of the galaxy, called the Orion Arm. It gets its name from the constellation Orion (in case that wasn’t obvious). This is prime real estate of the night sky, with the striking patterns of stars making for easy stargazing.
The Pleiades, Taurus, Orion, and his hunting dogs Canis Major and Canis Minor make their welcome return to the evening skies, spawning all manner of mythological tales. Sirius reminds us that it is the brightest star in the night sky (so it’s in charge), as it marks the collar of Canis Major, the ‘big dog’, while Orion has to negotiate with Taurus, the Bull, if he ever wants to take the Seven Sisters out on a date.
A waxing gibbous Moon will present on 21 December against this wonderful backdrop.
Venus, Saturn and Jupiter continue their impressive nightly display in the western sky.
The summer solstice occurs on 21 December. If you regularly watch the sunrise or sunset you’ll know that it rises and sets in a different place each day relative to the horizon. Due to a combination of the Earth’s tilt and orbit, over the course of a year the place against the horizon where the Sun rises and sets moves north, and then south, and back again, and the days where it reaches its maximum and turns around are the solstices. The word ‘solstice’ actually comes from ancient Latin – sol: sun, sistere: stand still.
In this case on 21 December the Sun has reached its southern most extreme. Following this, it will then appear to move north a little more each day. It can be a fun little project over the next few months to make a note of where the Sun sets. You don’t have to do it every day, but try it maybe once a week, note where the Sun has set against the horizon and watch it move week after week. You should catch the last of its southern motion before the turning point on the 21st and the subsequent northern motion.
The December solstice is also the day of the year with the most amount of daylight for those in the southern hemisphere, and from here on out the days will get shorter. Note that this doesn’t mean that sunset will be earlier – in fact, it’s still getting later as summer progresses, but the later sunrises each day will start to shave time off the length of the day, making this a maximum length day.
There is a solar eclipse this month on 4 December, but its path is so far out there that we won’t be able to see it. People in the far southeast of Australia will get a glimpse of a partial eclipse, but just barely.
Image: Time and Date
This month’s Full Moon occurs on 19 December when the Moon is at apogee – its greatest distance from Earth. Usually there is a lot of media attention when the full moon occurs at perigee (shortest distance), a ‘super moon’ as it is called. An apogee Full Moon is called a micro moon, because the Full Moon is at its furthest distance from Earth and thus looks smallest, but these don’t get anywhere near enough attention even though they are just as pretty.
What’s in a name?
Harry Potter and the Prisoner of Azkaban gets off to a frightening start with the news that fearsome criminal Sirius Black has escaped from prison. Along with this development, Harry is being stalked by a mysterious black dog. The big twist later in the story is that the dog turns out to be none other than Sirius Black. But you already knew this (ever since page 5), didn’t you? Sirius is the brightest star in the constellation of Canis Major, Orion’s hunting dog. It is often called the ‘dog star’. So, the name Sirius Black can almost literally be translated as ‘Black Dog’. Plot twist? What plot twist? Astronomy – ruining fantasy stories since 1687.
Dates of interest
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Moon close to Venus.
December 7
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Moon close to Saturn.
December 8
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Moon close to Jupiter.
December 9
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Summer Solstice.
December 21
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Launch of the James Webb Space Telescope.
December 22
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Celebrate the birth of the great Sir Isaac Newton.
December 25
Planets to look for
Venus, Saturn and Jupiter are still nicely lined up in the western sky in the evenings. The waxing crescent Moon adds its charm to make a nice alignment on 9 December.
Image: Be ready for a nice alignment on 9 December.
It must be the month for things turning around in the sky. Eagle eyed observers will be able to spot Venus entering retrograde motion from 19 December onwards. Use the stars making the teapot of Sagittarius as a reference to see Venus’s motion relative to the sky, and you should have no trouble spotting the change in direction.
Of course, Venus is not literally changing direction, it is overtaking Earth on its orbit around the Sun, and since we are a moving observer on an elliptical orbit watching another object moving on a faster elliptical orbit, it’s position relative to the background stars occasionally changes direction across the sky depending on the relative positions of it and us. And no, this won’t fix your failed marriage either.
Jupiter and Saturn continue to look great. You should take this opportunity to look at them through a telescope while they’re still there. There are very few astronomers who don’t answer, “The first time I saw Saturn’s rings through a telescope” when asked, “When did you know you wanted to be an astronomer?”
Whether it is the first time or the ten thousandth time, do yourself a favour and point something zoomy at these two planets.
Constellation of the month
Lepus the Hare
Lepus is in the smaller half of the constellations, and is located under Orion’s feet. Remember that since Orion is upside down in our sky this means it appears higher in the sky for us in the southern hemisphere.
The two brightest stars, Alpha Leporis and Beta Leporis are easy enough to see even in light polluted skies, and from there the rest of the asterism can be constructed. Beta Leporis is only one twenty-fifth the age of the Sun, but being several times more massive, has raced through it’s evolutionary life cycle and is now swelling to giant stages in the advanced stages of its life.
Alpha Leporis meanwhile is heavier, younger, and even more advanced in the stellar life cycle than its dimmer competitor. It’s greater mass has driven more furious energy consumption in the stars core, burning through its fuel quicker, and it now appears to be on the verge of going supernova, within a million years, perhaps.
Lepus doesn’t have any particularly prominent stories associated with it, apart from as an accessory to Orion’s hunting exploits. One day Orion and his dogs hunted a hare, that’s all there is to it. This leaves the door wide open for you to make up your own stories!
Object for the small telescope
Messier 79/NGC1904
Everybody loves a good globular cluster, and NGC1904 looks as fantastic as they get.
Located in the constellation of Lepus, it contains about 150,000 stars tightly packed together, 40, 000 light years away from us. There are around 150 globular clusters – agglomerations of thousands of stars in a spherical group – orbiting the Milky Way; ancient relics of the Universe whose role in galaxy evolution is still uncertain.
This cluster is a part of the hotly debated topic of the Milky Way Galaxy devouring the Canis Major Dwarf Galaxy (CMDG) of which NGC1904 is a part. Galactic cannibalism is common across the Universe and in this case all the stars, gas, dust and globular clusters of CMDG will be assimilated into our own galaxy. This fits nicely with the idea that globular clusters around the Milky Way came from the hearts of smaller galaxies ‘abzorbaloffed’ by the Milky Way.
The problem is that astronomers aren’t sure if the Canis Major Dwarf Galaxy even exists, suggesting observations could be due to the warped shape of the Milky Way instead. Amusingly, recent observations by ESA’s Gaia satellite hint that the warped shape of the Milky Way may be because of a galactic collision, just not with CMDG.
If you pull on a thread what will you unravel? Science lights the way. Anyway, it’s a beautiful sight through a telescope.
The James Webb Space Telescope
The time is finally here. After a troubled development, NASA’s James Webb Space Telescope (JWST) will be launching on 22 December, if all goes well. Cancel your Christmas plans, this is far more important! Launching from French Guiana atop the very reliable Ariane 5 rocket, the observatory is on a one-way trip to the Earth-Sun L-2 point to begin a long and successful career.
Image: If all goes well.
Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez
JWST has been plagued by delays and cost overruns. In one mishap the protective insulating sunshield ripped, delaying the project by a year. Most recently, a clamp on the launch vehicle adaptor sprung loose unexpectedly, causing unplanned-for vibration in the $10 billion spacecraft.
The telescope is so large it has to be folded up to fit inside the rocket payload faring, so must complete a spine-tingling deployment process before it is ready for use. The L-2 point is 4 times further away from Earth than the moon, which means that once Webb is launched it will be unable to be visited and serviced by astronauts, unlike the Hubble Space Telescope which had multiple servicing missions to upgrade its equipment and extend its life.
Image: An exciting Christmas present! Credit: ESA
The JWST is an infra-red telescope, so it sees a lower energy part of the spectrum than our eyes. This allows it to do what Hubble cannot: it will be able to peer through the cosmic dust around protostars to see planets and stars in the earliest stages of formation, as well as look to the most distant galaxies in the Universe which have been redshifted beyond visible light and out of Hubble’s range, the furthest away in space and the furthest back in time. Studying the formation of galaxies, stars and planets will lead to a better understanding how the Universe got to be the way that it is today, and will reveal secrets of the answer to the question that drives us all: how did we get here?
Meanwhile in the Scitech Planetarium
You may be aware that in its past life the Scitech Planetarium used to be an Omnimax theatre. We decided to crack open the storage crates and bring the old projector out for a look see. Behold its beauty.
Credit: Scitech
As you can see it needs a dust off and some TLC, but hopefully we can get some activity out of it. The plan is to put in on display where you can press a button and *something* will happen. Watch this space.
Other space news
What’s that? A history of Soviet rocket engines? Yes Please!
The Bureau of Meteorology has declared a La Nina event is taking place. This means cooler waters in the eastern pacific while an overabundance of warm water and air in the western Pacific, leading to wetter weather in north-eastern Australia. This is the counterpart to the El Nino oscillation and the reason why it’s been a bit wet lately.
NASA’s Dart mission launched successfully on a SpaceX Falcon 9 rocket on a collision course with the Didymos-Dimorphos asteroid system. Avenge the dinosaurs!!
A Russian anti-satellite missile test “succeeded” in destroying a low earth orbit satellite, creating thousands of pieces of debris. This appalling demonstration deservedly drew international criticism, even endangering Russian cosmonauts in the International Space Station.
Up and coming rocket company Astra finally succeeded in getting a spacecraft to orbit, after their last attempt turned into a lawn mower.
New Zealand based Rocket Lab also succeeded in launching to orbit their beautifully named ‘Love at First Insight’.
Musical chairs on the International Space Station as Crew 2 returned and Crew 3 was launched.
Blue Origin and Jeff Bezos failed in their lawsuit to stop NASA from following through with their plans to use SpaceX to build Lunar Starship to land astronauts on the Moon as part of the Artemis Program and the Human Landing System. SpaceX and NASA can now proceed to actually design and build Lunar Starship.
SpaceX conducted a full 6-engine static fire test of (regular) Starship. The beast is slowly coming to life.
Image: That’s just a test fire.
Credit: SpaceX
