March 2024
The Sky Tonight - March 2024
April brings us into the season of Djeran, characterised by arrival of some much-needed cooler nights. The eastern sky is the …
ExploreNew Moon
January 3
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The casual observer
Summer is in full swing as the outer arms of the Milky Way become easier to see in the eastern sky at reasonable times of night. The Southern Cross is starting to climb above the horizon and is visible in the southeast. Drawing a line from the cross, past Canopus, through Sirius to Betelgeuse allows you to trace out the Milky Way’s outer regions.
Image: Early January presents this beautiful view from the Southern Cross to Orion.
Not far from Saturn and Jupiter, early in the month, comet C/2021 A1 (Leonard) continues its appearance for keen sky-watchers. You will probably need binoculars or a small scope to see it if you are in a light polluted area.
The fairly minor Eta Carinids meteor shower peaks on 21 January with several meteors per hour to be expected.
Mercury is technically visible in the western sky after sunset early in the month, but it’s so low to the horizon that your neighbours fence may be the biggest problem to overcome if you want to see it.
Perihelion
Earth reaches perihelion on 4 January, it’s closest distance to the Sun. Because Earth’s orbit is slightly elliptical, we are sometimes closer to and sometimes further away from the Sun, and 4 January is when we are closest, at about 147 million km. From here on out Earth will be further away from the Sun, until it reaches aphelion on 4 July at 151 million km, and the cycle repeats.
A surprising number of people think this is what causes the seasons. It “makes sense”, doesn’t it? Earth being closer to the Sun means it will be warmer, and being further away from the Sun means it will be colder. Boom.
It’s also especially appealing since perihelion occurs at the peak of Australian summer; the Sun is literally closer to you than it is in the middle of winter. This idea, of course, falls flat when you probe a little deeper, like asking why the seasons are opposite in the different hemispheres. While it is true to say that the distance to the Sun does influence temperature, the effect of Earth’s tilt is much more significant and is the real reason for the seasons.
For the mathematically minded, the temperature goes only as the inverse of the square root of the distance, while a back of the envelope blackbody calculation gives the effect of the tilt as the fourth root of the cosine of twice the tilt angle (not accounting for albedo or any other real things). Crunching the numbers for Earth we get about a 4-degree Celsius difference in temperature from perihelion to aphelion, substantially less than the 56-degree difference from peak summer to dead winter predicted by the tilt calculation. It’s hardly a perfect model, but the point is it’s all because of the tilt.
Dates of interest
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Moon above Mercury, next to Saturn.
January 4
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Earth at perihelion.
January 4
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Moon above Jupiter.
January 6
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Eta Carinids meteor shower.
January 21
Planets to look for
Venus has finally set in the west and will show its face again later in the month in the western sky just before sunrise.
Jupiter and Saturn stick out like sore thumbs in the western sky in the evenings, soon to be setting below the horizon for a long absence from the night sky, so make sure you take the opportunity to get a glimpse of them while they are still visible.
Mars has properly emerged from its trip behind the Sun late last year and is now visible in the eastern sky in the early mornings. If you are a lark or a sociopath, you can catch it at about 4am. Sunrise hovers around just after 5am this month so don’t be late if you want to see it.
Constellation of the month
Carina
Carina is a large constellation in the southern skies, and forms the keel of the boat Argo Navis from the story of Jason and the Argonauts. Argo Navis was once a single giant constellation but is now divided into Carina, Puppis and Vela.
The brightest star in Carina is Canopus. It is the second brightest star in the night sky, and is actually significantly brighter than Sirius in terms of absolute magnitude, but it is just so much further away – 310 light years compared to Sirius’s nearby 8.7 – that it’s relative magnitude is fainter by comparison.
We could recount here the story of Jason and his Argonauts in the quest for the golden fleece and the throne of Iolcos. But let’s not. Instead, let us focus on the story of a boy called Paul Atreides and his journey to a planet called Arrakis.
Arrakis is the third planet from Canopus and is the desert home of the Fremen, the sandworms, and the spice melange. Paul may be the long sought Kwisatz Haderach, the one who can be many places at once. At least, this is the story told in the sci-fi epic, Dune. It’s nice to look up at Canopus every night and give a silent nod to the magnificent story told there.
Carina is home to a number of fascinating objects, the most notable being the Grand Carina Nebula. This complex nebula is home to many exciting features including the star Eta Carina and its surrounding Homunculus Nebula, the open clusters Trumpler 14–16, and the Keyhole Nebula.
Eta Carina is notoriously unstable and is expected to go supernova sometime in the next few hundred thousand years. Perth gravitational wave astronomer Emeritus Professor David Blair wrote an amusing story about this possibility.
And finally, of course, there’s the Defiant Finger.
Image: “This Carina sub-cloud is particularly striking partly because its clear definition stimulates the human imagination (e.g., it could be perceived as a superhero flying through a cloud, arm up, with a saved person in tow below).” – APOD, 2003.
Credit: Hubble Heritage Team (STScI/AURA), N. Walborn (STScI) & R. Barb (La Plata Obs.), NASA
Object for the small telescope
C/2021 A1 (Leonard)
You’ve probably heard of this comet by now after its closest approach to Earth on 18 December. Discovered in January 2021, this long period comet is making its first entry to the inner solar system in about 80,000 years. It is moving on a retrograde orbit so travels the opposite way around the sun to Earth and most other things in the solar system.
Image: 5 January presents a nice alignment of planets to backdrop your comet hunting!
The comet has shown sporadic signs of activity and is hovering around magnitude 5-6, faint but certainly something you can see with binoculars or a small scope in a good sky. The comet reaches perihelion on 3 January, after which it will leave the solar system never to return. Catch it while you can!
Carina Nebula
A beautiful jewel in the southern sky, the Carina Nebula is a must-see over the next couple of months. An intense burst of star formation several million years ago has resulted in a number of massive stars estimated to be 50–100 solar masses.
These stars are furiously fusing material in their core and giving off intense ultraviolet radiation which is ionising the rest of the gas in the nebula. As this gas re-emits the light at lower energy wavelengths the nebula takes on a reddish glow to the sharp eyed.
Image: Carina Nebula. Credit: Sky and Telescope
And if you like what you see, then you REALLY want to see this VLT image of the Carina Nebula in all its glory.
Starship orbital test flights in 2022
If you aren’t regularly keeping up to date with SpaceX, consider this:
Image: Starship 6-engine static fire test. Super Heavy booster in the foreground. Credit: SpaceX
After perfecting the Falcon 9 rocket, SpaceX announced their ambitious plans for a super heavy lift vehicle to take humans to Mars. At inception it was colloquially referred to as the BFR, the Big … Rocket, and over time it has morphed into Starship.
Starship Super Heavy engine steering test pic.twitter.com/VG4RQAGuyk
— Elon Musk (@elonmusk) December 18, 2021
Credit: Elon Musk
The completed vehicle consists of the upper stage ‘Starship’, sitting atop the first stage ‘Super Heavy’ booster, and the whole thing is also confusingly called ‘Starship’ as well.
Currently, Ship 20 seems to be ready to fly, and booster 4 is undergoing tests at the launch site in Texas, with flight 4-20 expected in early 2022.
The (almost) ludicrous number of engines on starship will give it a thrust of about 5500 tonnes, around twice as powerful as the Saturn V moon rocket.
Image: Heavy lift vehicle comparison with capacity to LEO listed underneath. Credit: Thorenn
Throughout 2021 SpaceX have been at a furious pace of building, testing and developing starship, with a few casualties along the way.
The rocket hasn’t gone to space yet, but SpaceX will likely receive approval from the USFAA to conduct 5 starship orbital launches in 2022 pending completion of the environmental review.
Starship is powered by the impressive Raptor engines, a type of engine that has never flown to space before, so SpaceX are breaking new ground here with this technology.
If you think the Falcon 9 landing on a barge was a ridiculous idea, Starship is designed to be fully reusable by being snatched out of the sky by a giant pair or arms, affectionately called ‘the Chopsticks’ by Starship fans.
Image: The Chopsticks atop the tower Mechazilla, ready to catch the descending Starship and place on top of the Super Heavy booster for reuse. Credit: ErcX
It is an interesting case study in engineering: SpaceX have prioritised the build-test-blowthehellup model of the design process, the exact opposite process to NASA who are building the comparably sized Space Launch System – a meticulously engineered project that began in in 2011 and has yet to perform a single test flight. The first SLS test flight, Artemis 1, is currently scheduled for March 2022.
This is not NASA’s failure or shortcoming, however. NASA is constrained by limited funding and a public opinion that wouldn’t appreciate rockets exploding on the launch pad. Consequently, NASA is forced to adopt the ‘everything must be perfect’ approach to rocket engineering. If only more people understood that failure is part of the design process, NASA might already be back on the Moon and on its way to Mars.
If the whole thing actually works, and that’s a medium sized ‘if’, this really will be the dawn of a new space age. Success is not guaranteed, but excitement is!
Video: Animation of starship orbital test flight. Credit: -bass Productions
Meanwhile in the Scitech planetarium
It was time to change over our projector lamps. To produce an image on the screen of the planetarium we have two massive projectors outputting about 20,000 lumens each. The light source for these beasts is a xenon lamp that sits in the back of the projector.
Ionised xenon gas gives off a near continuous spectrum across visible wavelengths somewhat similar to sunlight, and for that reason is an excellent choice for film projectors because the colour levels are naturally balanced for what our eyes have evolved to see. The difficulty is that to get a good amount of light and ionisation you need to keep the xenon pressurised and run a tremendous amount of current through it.
Behold the xenon lamp.
Credit: Scitech (McKie)
At room temperature, the gas inside the bulb is at a pressure of 10 atmospheres. When operating, electricity arcs from the pointed tip (cathode) to the rounded knob (anode) and ionises the xenon in the process. This also heats the gas to several hundred Celsius and raises the pressure to about 30 atmospheres.
These pressures and temperatures take their toll on the materials, and the lamps need to be swapped out every few months. You can even see in the picture above; the part of the anode directly opposite the cathode, where the arc contacts it, is shiny because it has partially melted. No small feat given that it is made of tungsten!
This is a long way of saying that these lamps are not mucking around and are extremely dangerous because of their potential to explode, and require special training and equipment for handling and disposal.
Image: Felt cute, might change a xenon lamp later.
Credit: Scitech
Other space news
THE JAMES WEBB SPACE TELESCOPE WAS SUCCESFULLY LAUNCHED ON 25 DECEMBER!!!
New Zealand based Rocket Lab released an excellent video unveiling their concept for The Neutron Rocket – A rocket for 2050, today.
ICRAR scientists capture black hole eruption spanning 16 times larger than the full Moon.
NASA’s Imaging X-Ray Polarimetry Explorer (IXPE) satellite was launched on a SpaceX Falcon 9 rocket. IXPE will measure the polarisation of cosmic X-rays to tease out details about what sources are creating them.
Soyuz MS-20 launched Cosmonaut Alexander Misurkin and two Japanese tourists to the International Space Station for a 12 day stay.
A solar eclipse occurred on 4 December. This eclipse was also notable for the apparent east to west movement of the shadow caused by it falling on the far side of the earth, a combination of the earths tilt and the eclipses extreme location.
