January 2025
The Sky Tonight - January 2025
January continues the season of Birak, and the hot weather isn’t going anywhere anytime soon. The night sky presents a parade …
ExploreNew Moon
September 3
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The casual observer
September brings us into spring and continues the season of Djilba, the season of conception. The rainy days are ongoing but will noticeably be clearing up by the end of the month, and the night sky presents a plethora of interesting sights.
Saturn reaches opposition on Sep 8, meaning if you point one hand at the Sun and the other at Saturn, you will be pointing in opposite directions. This means that Saturn rises in the east as the Sun sets in the west and it will be visible all night for this month, making this the best time of year to view the planet. At a magnitude of about 0.58, it is noticeably yellow to the naked eye as it climbs through the eastern sky in the evenings, and you can use the nearby star Fomalhaut as a reference.
Image: Saturn and Fomalhaut in the eastern sky during the September evenings.
Credit: Stellarium
The Full Moon on Sep 18 is a ‘supermoon’, the term given when the Full Moon occurrs when the Moon is at perigee, the point in its orbit when it is closest to Earth and thus looks bigger in the sky. Humans are surprisingly bad at judging the size of things in the sky, so “looks bigger” is a relative term. You really need a before and after to tell the difference in size – it will about 14% larger – but it will be noticeably brighter, about 30%, as the larger size and shorter distance bring appreciably more light.
Image: Super Full Moon (left) and an average Full Moon (right).
Credit: Stellarium, Smith/Scitech
The Spring equinox occurs on Sep 23. The equinox marks the point in Earth’s orbit where the Sun passes directly over the equator. Seen from space, the terminator (or day-night line) is straight up and down from the north pole to the south pole. This also means that on this day there will be exactly 12 hours of day and night almost everywhere on Earth. From here on out, Earth’s continued motion along its orbit will make the Sun continue to appear to drift in a southerly direction, moving it higher and higher in the sky, bringing with it the warmer days that lead into summer.
Image: Earth seen from space during the equinox.
Credit: NASA, EUMETSAT
The Milky Way still makes for great viewing in the evening sky, moving more to the west as the month goes on. In the southeast you can get a good view of the southern birds – Phoenix, Pavo, Grus and Tucana – before turning and facing the northeast and using the bright star Altair to guide you to Aquila, the eagle, and together these should satisfy all of your bird cravings.
Image: The birds of the spring night sky. Aquila in the northeast, and the Southern Birds in the southeast. You can use also use Achernar, Fomalhaut and even Saturn as a reference.
Credit: Stellarium
ISS sightings from Perth
The International Space Station passes overhead multiple times a day. Most of these passes are too faint to see but a couple of notable sightings* are:
| Date, time | Appears | Max Height | Disappears | Magnitude | Duration |
| 1 Sep 7:08 PM | 10° above SW | 63° | 38° above ENE | -3.6 | 4.5 min |
| 15 Sep 05:38 AM | 10° above NNW | 54° | 10° above SE | -3.0 | 6.5 min |
Table: Times and dates to spot the ISS from Perth
Source: Heavens above, Spot the Station
*Note: These predictions are only accurate a few days in advance. Check the sources linked for more precise predictions on the day of your observations.
Dates of interest
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Moon next to Venus
September 5
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Saturn at opposition
September 8
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Moon occults Antares
September 10
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Moon near Saturn
September 17
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Venus next to Spica
September 18
Planets to look for
Venus is shining brightly in the evening sky all month. You can see it in the western sky, chasing the Sun over the horizon and setting about 8pm. After looking at Venus you can turn around and face east to see Saturn rising. Its opposition on Sep 8 means that this is the best time of year to view the planet. The appearance of the almost-Full Moon nearby on Sep 17 makes for a nice sight.
Image: Saturn and Moon in the evening sky on Sep 17.
Credit: Stellarium
The morning sky presents Mars and Jupiter for great viewing. After their close approach on Aug 15, the noticeably brighter Jupiter is racing higher in the sky while the fainter red Mars still hangs about a handspan above the horizon. Uranus is there as well but you will need a telescope to see it. The whole show is backdropped by Orion and Taurus
Image: Jupiter and Mars in the morning sky, joined by Uranus and some familiar stars to guide the way.
Credit: Stellarium
Mercury is mostly lost in the glare of the Sun this month, but if you’re really keen you can see it peek above the eastern horizon just before sunrise for the first half of the month.
Constellation of the month
Corona Australis – The Southern Crown
Corona Australis is the 9th smallest constellation in the night sky and is named as the southern equivalent of Corona Borealis that we covered last month. Located between Sagittarius and Scorpius, it is still recognisable as a faint but distinct semicircular pattern of stars.
Image: Corona Borealis is located between Sagittarius and Scorpius in the night sky.
Credit: Stellarium
In practice you might find it more useful to look for the teapot in Sagittarius and the hook of the Scorpion and look somewhere on between.
Image: Star patterns to look for to guide the way to Corona Australis.
Credit: Stellarium
Corona Australis is a faint constellation, its brightest star Alphecca Meridiana is a large, hot, main sequence star whose luminosity of 30 times greater than the Sun is dulled to a magnitude of only 4.1 by its distance of 125 light years from us, so you want to be sure to observe this constellation on a moonless evening.
Corona Australis is notable for the Corona Australis Molecular Cloud, an enormous agglomeration of dust and gas about 400 light years away that is actively forming hundreds of stars. Some parts of the cloud block starlight from more distant stars behind, while other parts of the cloud reflect brilliant blue from nearby hot stars giving the cloud a dark appearance with a beautiful blue centre. In the same part of the sky, the much more distant globular cluster NGC 6723 shines along the same line of sight.
Image: The Corona Borealis Molecular Cloud, with the blue reflection in the centre standing out from dark surroundings (not to be confused with blue stars on the periphery), and the Chandelier Globular Cluster (NGC 6723) in the top right.
Credit: Ivan Bok, CC BY 4.0, via Wikimedia Commons
Object for the small telescope
Saturn
Saturn’s location at opposition makes for great viewing. Not only are Earth and Saturn the closest together they’ll be all year, we are seeing the planet face on, capturing its entire daylight side. The magnitude peaks at 0.58, brighter than most stars in the sky and the planet has a distinctly yellowish colour, making it easily stand out from any nearby stars.
Image: Saturn as it appears during September, with some moons shown too. Note the full illumination of the planet and the narrowness of the rings.
Credit: Stellarium
Saturn is approaching its own equinox and consequently we are viewing the planet at a very shallow angle, so the rings appear very narrow when viewed from Earth. They will appear to get narrower and narrower until Saturn reaches equinox on March 6, 2025 and the rings will be edge on to us, seemingly disappearing from around the planet because they are so thin. Unfortunately, by the time this happens, Saturn and Earth will have moved to opposite sides of the Sun, and we won’t get a very good view of it. Which is another way of saying enjoy the view tonight while you have the chance.
Moon-Antares Occultation
On Sep 10 the Moon will pass in front of, or ‘occult’, Antares, the bright heart of the Scorpion. You need to be quite prompt with this; the occultation begins at exactly 10:05 pm and Antares re-emerges at 11:08pm, so make sure you are ready for this window.
Video: Lunar occultation of Antares on Sep 10.
Credit: Smith/Scitech, Stellarium.
EscaPADE to Mars on the New Glenn
If all goes well, the Escape and Plasma Acceleration and Dynamic Explorers (EscaPADE) mission will soon be launching to Mars on the maiden flight of the New Glenn rocket from Blue Origin. That’s quite a sentence so let’s unpack it piece by piece.
EscaPADE is a NASA mission consisting of two identical spacecraft, about a metre in size, named Blue and Gold, whose purpose is to study the magnetic and plasma environment around Mars. Scientists want to know how Mars’s magnetic field interacts with the solar wind – the constant stream of high energy charged particles that emanates from the Sun – and how this interaction affects Mars’s atmosphere.
Unlike on Earth, where our planet’s strong magnetic field comfortably deflects most of the solar wind safely around us, the weak and inconsistent Martian magnetic field is nowhere near as effective, allowing the solar wind to interact much more strongly with the atmosphere of Mars and, over millions of years, strip it away from the planet.
Image: Mars’s magnetic field and atmosphere interact with the solar wind in a complex way.
Credit: NASA’s Scientific Visualization Studio. Image of Martian magnetic field line interactions courtesy of Anil Rao/Univ. of Colorado/MAVEN/NASA GSFC
Ultimately the goal is to understand more about the puzzling history of Mars and its water. As a result of billions of years of exposure to the solar wind, Mars as we know it today has an extremely tenuous atmosphere, 150 times thinner than Earth. Consequently, the air pressure is so low that that liquid water can’t exist on the surface of the planet – it just immediately evaporates away or freezes, or both. There are no rivers or lakes on Mars today. However, the extensive presence of sedimentary rocks and clay minerals – things that can only form in bodies of liquid water – tells us the planet used to have great bodies of water on its surface, meaning the atmosphere of Mars in the distant past was once much thicker and at a high enough pressure to be able to support liquid water. Thus, the need to understand how Mars lost its atmosphere.
Image: Sedimentary rocks on Mars photographed by the Perseverance Rover.
Credit: NASA/JPL-Caltech
Blue and Gold are both equipped with magnetometers to measure the magnetic field strength around Mars, as well as instruments that measure the energy and density of ions and plasma around the planet. After an 11-month flight to Mars the two spacecraft will operate a year-long science mission collecting data around the planet. Cleverly, the spacecraft will spend 6 months orbiting Mars in the same orbit, allowing them both to collect measurements from the same part of the magnetosphere, and then they will each shift to different orbits, allowing for measurements of different and distant parts of the magnetosphere at the same time.
Image: Artistic impression of the identical Blue and Gold spacecraft.
Credit: Rocket Lab.
Interestingly, the spacecraft were supposed to be hitching a ride on the same launch as the Psyche spacecraft (which we wrote about here), originally planned for liftoff in July 2022. Delays in preparing the Psyche mission forced the launch to be pushed back to October 2023, by which time Mars was in the wrong position and EscaPADE could no longer hitch a ride, so NASA had to find a new launch vehicle. And this is where Blue Origin stepped in, seeing it as a good opportunity for the maiden test flight of New Glenn.
Blue Origin – owned by Jeff Bezos – is an aerospace company mostly known for their space tourism flights on the New Shepard rocket. You know, the one that is shaped like an aubergine.
Image: New Shepard in flight.
Credit: Blue Origin
Meanwhile, for the past decade or so, they have quietly (and somewhat secretively) been developing the New Glenn, the much, much, much bigger sibling of New Shepard. Where New Shepard is a tiny rocket, ‘only’ 18 metres tall, that launches tourists 100km straight up and down, New Glenn is a 100-metre-tall heavy lift vehicle designed to haul satellites and spacecraft into Earth orbit and beyond. If all goes well, New Glenn will be taking the Blue and Gold EscaPADE spacecraft to Mars on its maiden flight on Sep 28.
Image: New Glenn (right) compared to the SpaceX Falcon Heavy (middle) and the New Shepard booster (left).
Credit: Everyday Astronaut
At 7 metres in diameter and capable of launching 45 tonnes of cargo into Low Earth Orbit, New Glenn is comically overpowered for the 2 x 500kg spacecraft of EscaPADE, but a test flight is a test flight. New Glenn is designed to be partially reuseable, with the first stage booster separating and landing on a barge in the middle of the ocean, exactly like the SpaceX Falcon 9, while the second stage continues to orbit to deploy the cargo before deorbiting and burning up in the atmosphere so as not to create more space junk.
Image: Hypothetical flight profile of New Glenn.
Credit: Blue Origin
New Glenn is part of the latest generation of rockets developed to use methane as a fuel. Blue Origin has developed a new engine, called the ‘BE-4′, specifically for New Glenn, and 7 BE-4 engines will used to get the rocket off the ground. Interestingly these engines are also used by United Launch Alliance on the Vulcan Centaur rocket.
Image: BE-4 engine in production.
Credit: Blue Origin
As of late August, the EscaPADE spacecraft have been delivered to Blue Origin ready to be installed into New Glenn, and launch is planned for Sep 28, though rocket launches tend have a habit of getting delayed, especially first test flights. Because of the orbits of Earth and Mars, the window of opportunity to launch something to Mars, the launch window, as it is called, is open from late September through to November, so one way or another we’ll see the whole thing take flight soon.
Image: New Glenn on the pad.
Credit: Blue origin
In case you’re wondering…
The New Shepard and New Glenn get their namesakes from American astronauts. Alan Shepard was the first US citizen to go to space. His flight on the Freedom 7 spacecraft launched (more or less) straight up and down, just like the new Shepard does today. John Glenn was the first US citizen to orbit Earth on the Friendship 7 spacecraft, as New Glenn intends to do.
