April 2025
The Sky Tonight - April 2025
April brings us into the season of Djeran, characterised by cool evenings giving way to cooler mornings, if we’re …
ExploreFirst Quarter
May 4
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The casual observer
May continues the season of Djeran – the season where the cooler weather begins. Maybe it will get here eventually? Please?
May is all about Star Wars. The perfect night to go outside is May 4, also known as Star Wars Day (May the Fourth be with you). On this date, start your night sky observations by looking to the north-northwest where you will see three pairs of interesting things – Mars and the Moon, as well as the constellations of Gemini and Canis Minor, both identified by two easy-to-see stars each.
Image: The northern evening sky on May 4. Credit: Stellarium
The First Quarter Moon is the brightest object by far, and nearby is the fainter, red Mars. Interestingly, scientists have recently proposed a new model for why Mars is red. Instead of hematite – a ‘dry’ kind of iron rust with no water locked up inside – scientists have found evidence of ferrihydrite, a ‘wet’ iron rust that has water locked up in its molecular structure. This is exciting because it is another piece of evidence suggesting that Mars once had great oceans on its surface.
To the lower left of the red planet is the red giant star Pollux, in Gemini. Compared with its ‘twin’ Castor, a closer look reveals the twins couldn’t be more different. The single, enormous, red giant star Pollux is vastly different to the six-stars-in-one system that we see as the single ‘star’ Castor.
Image: The ‘star’ Castor is actually six stars all bundled together. Credit: NASA/JPL-Caltech; edited by Nicholas Beeson
If you time your observations right, at exactly 7:13 pm on May 4 you’ll see a bright light moving across the northwestern sky. Passing between Castor and Pollux it will slide under the Moon before fading out of sight in the northern sky. That’s no Moon, it’s a space station. Specifically, the International Space Station. See the table below for more information.
Image: Instantaneous location of the International Space Station (blue box) at 7:13:44 pm on May 4
Finally, Canis Minor shines with the bright star Procyon and the fainter Gomeisa. These make up the body of the Small Dog in the sky and the companion to Canis Major which we wrote about here.
Image: Yeah, looks like a dog to me. There’s some serious “somebody else’s problem” energy in the star maps of this part of the sky. Credit: Stellarium
Next to this spectacular sextuple is the constellation of Leo, the lion. A zodiacal constellation, Leo is one of the few constellations that actually kind of looks like what it is supposed to represent (albeit upside down from our point of view)
Image: Leo, the lion, in stick figure. Moon and Mars for reference on May 4. Credit: Stellarium
After you’ve taken in these night sky delights, you can either go to bed early or stay up all night. Either way, the Eta Aquarids meteor shower puts on a show before sunrise on May 5, but I’m still calling it the night of May 4.
Image: Apparent location of the sky of the Eta Aquarids meteor shower at 5am on May 5. Venus and Saturn guide the way.
This is a vibrant meteor shower whose bright streaks actually originate from the illustrious Halley’s Comet. You can think of a comet as a dirty snowball, or, if you prefer, a snowy dirtball. As Hally’s Comet moves through our Solar System on its approximately 75-year orbit, it occasionally passes close enough to the Sun to get hot enough for some of the fragile material in the comet to boil away into space. This ‘outgassing’ carries with it lots of dirt and pebbles which are left free floating in space. Eventually, some of these pieces of dirt collide with Earth and light up our sky as they slam into the atmosphere, causing a meteor shower.
The Eta Aquarids meteor shower is not to be missed. In good conditions you should see a meteor every minute or two. These meteors move fast across the sky, and the shower actually lasts all month. The best way to see it is to look to the east before sunrise on May 5 or 6, but don’t panic if you forget to set the alarm on these days, you can try again the next day throughout the month of May.
While you are watching the meteor shower, you can’t not-see Venus. Fabulously bright and dominating the eastern morning sky, this Earth-(sort of)-twin makes for wonderful viewing as it glows against the twilight of sunrise. At Scitech we get a lot of phone calls and emails asking about ‘the big bright thing in the sky’ during the early morning or evening, depending on the time of year. It “seems to be following me.” It’s “there every morning. Almost white it’s so bright.” These are all sightings of Venus. It takes its name for the godess of love, so named because it burns so bright, just like the fires of passion that love ignites in our hearts.
This also reminds me, I need to set my automatic replies:
Image: Sorted.
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 |
| 2 May 7:10 PM | 10° above SW | 82° | 82° above NW | -3.8 | 3 min |
| 3 May 6:21 PM | 10° above SW | 49° | 12° above ENE | -3.5 | 6 min |
| 4 May 7:10 PM | 10° above WSW | 22° | 10° N | -1.3 | 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.
If you are wondering why the station disappears in the middle of the sky on May 2, read our article here.
Dates of interest
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Star Wars Day, Moon near Mars. Eta Aquarids meteor shower peaks tomorrow morning
May 4
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Eta Aquarids meteor shower peaks before sunrise
May 5
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Eta Aquarids meteor shower peaks before sunrise
May 6
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45th anniversary of Star Wars: Episode V - The Empire Strikes Back release in cinemas
May 21
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Moon near Saturn and Venus
May 23
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48th anniversary of Star Wars: Episode IV - A New Hope release in cinemas
May 25
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42nd anniversary of Star Wars: Episode VI – Return of the Jedi release in cinemas
May 25
Planets to look for
Mars makes for decent viewing in the north-northwest this month. You can see it next to the Moon on May 4 as described above.
Jupiter is visible for an hour or so after sunset in the northwest. Catch it this month before it disappears behind the Sun. It will reappear in the eastern sky before sunrise in early July.
Image: Mars and Jupiter in the northwestern evening sky on May 4. Credit: Stellarium
Venus and Saturn are visible in the eastern sky before sunrise. The bright Venus dominates the scene while the fainter Saturn hangs a bit higher in the sky above it. Mercury is also there closer to the horizon, but it moves behind the Sun in the latter part of the month and gets lost in the glare.
Venus and Saturn separate noticeably in the sky this month. Interestingly, this is the opposite of what it looks like. It appears that Saturn is racing higher in the sky, and Venus is standing still, almost hovering above the horizon. What’s really happening is Earth’s movement around the Sun makes Saturn appear to move quite a lot. Not to be outdone, Venus moves even faster, effectively ‘cancelling out’ the movement of Earth and making it appear to hang in the same place. This is much more obvious if you look at the background stars and compare where Saturn and Venus are against them.
Video: A Saturn – static point of view shows Venus is moving much faster against the background stars compared to the ringed planet which only moves a small amount. Motion of the background stars is because of Earth’s movement around the Sun. Credit: Smith/Scitech, Stellarium
Constellation of the month
Leo – The Lion
Leo is a large constellation visible in the northern sky during Autumn. It is a very distinctive constellation whose stars from an upside down question mark sitting next to a triangle and are collectively seen as a lion.
Image: Leo, the Lion, with the question mark (left) and triangle (right) easily discernible.
In mythology, Leo is often seen as the Nemean Lion associated with the story of Heracles (Hercules) and his twelve labours. The first labour of Hercules was to kill the lion, a task made infinitely more difficult by the fact that the lion’s hide could not be pierced by weaponry, rendering swords and spears useless. Problem solving on the spot, Heracles strangled the lion with his bare hands, where upon Zeus placed it in the sky as Leo.
The brightest star in Leo is the magnitude 1.35 Regulus, meaning ‘little king’. This 4-star system consists of two pairs of stars orbiting each other and is the namesake of Regulus Black from the Harry Potter stories. One could argue that the star is better described by its Arabic name Qalb al-Asad, meaning ‘the heart of the lion’.
Leo is a treasure trove of fascinating sights, including the Cosmic Horseshoe. This peculiar observation is what happens when you have one very distant background galaxy on almost exactly the same line of sight as a foreground galaxy.
Image: The Cosmic Horseshoe. Credit: NASA, ESA
Einstein’s general relativity predicts that the gravity of a massive object – like a galaxy – should bend the path of light as it passes by. In this case, the reddish galaxy in the foreground (excitingly named LRG 3-757) has enough gravity to act like the lens of a magnifying glass, focussing the light from the background galaxy in a process called gravitational lensing. A slight misalignment from exact line of sight leaves a small gap at the top, giving the horseshoe appearance. A perfectly circular lensed galaxy is called an Einstein Ring. The effect is that it allows us to peer around the foreground galaxy to see what is behind it, albeit in a very distorted view.
Image: Schematic diagram of gravitational lensing. Imagine this happening on every side of the massive object and you can see how a ring of light is formed. Credit: NASA
Speaking of gravity and galaxies, Leo is also home to the Leo Cluster – a group of about 70 galaxies bound together by gravity located about 300 million lightyears away.
Image: The Leo Cluster of galaxies and many more distant background galaxies. Apart from two stars, marked by horizontal lines, every other point of light is a galaxy. Credit: By Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev – Own work, CC BY-SA 4.0
Together with the Coma Cluster – a collection of about 1000 galaxies located in the neighbouring constellation of Coma Berenices – they form part of a larger cluster of galaxies called the Coma Supercluster which itself is part of an even larger cluster of galaxies called the Great Wall. Astronomers group clusters of galaxies together based on their proximity and motion through space to better understand the large-scale structure of the Universe and how it got to be the way that it is today.
Object for the small telescope
The Leo Triplet – A cosmic trio of galaxies far, far away
The Leo Triple is a throuple of galaxies close together in both line of sight and real-life proximity. Consisting of the Hamburger Galaxy (yes, seriously) and the Messier objects M65 and M66, the Leo trio are all located about 35 million lightyears away.
Image: The Leo Triplet with M65 and M66 (top right and middle right) and the Hamburger Galaxy (middle left). It does kind of look like a hamburger. Credit: Chuck Ayoub – Own work, CC0
A long time ago, a close encounter between M66 and the Hamburger Galaxy severely distorted both of them. The huge, bright streak trailing behind the Hamburger Galaxy, called a tidal tail, consists of material pulled from the galaxy by the gravity of M66. Meanwhile, M66 shows obviously distorted spiral arms with more dusty material in them and an unusual distribution of gas compared to other galaxies. A great target for the keen stargazer.
Fiction meets fact: Finding Tatooine-like planets and successfully navigating an asteroid field.
The planet Tatooine in the Star Wars saga famously has two suns. Despite sounding like something that would only appear in science fiction, astronomers had previously discovered 16 planets in a two-star system just like Tatooine, and in April 2025, astronomers from the UK and France presented evidence for the 17th example. But this one has a twist, literally. Rather than orbiting the stars in the same plane, like peas all rolling around on a plate, this proposed planet jumps up out of the plate and moves at a right angle to the orbit of the stars. Theoretical models had suggested this was possible under the right set of circumstances, and now it just might be confirmed.
Image: Artistic representation of the planet orbit (orange) tipped sideways to the orbit of its stars (blue). Credit: ESO
Scientists had already previously found disks of material in strange orbits like this, so from a certain point of view it was only a matter of time before a planet in this inclination was discovered.
But things do get more unusual though. The ‘stars’ in this system, excitingly named 2M1510(AB), are technically not stars in the usual sense of the word. They are brown dwarfs – objects that are much, much heavier than even the biggest planets, but still not quite big enough to be main sequence stars. They exist in a strange no-man’s-sky between the two concepts.
Image: Artist impression of a brown dwarf. Not quite a star, not quite a planet. Credit: NASA
But for a movie made when Pluto was still a planet and we hadn’t found any planets around other stars, we have to give a nod for the surprisingly prescient foresight of Star Wars.
On the contrary though, despite C3P0’s urgent insistence, the possibility of successfully navigating an asteroid field is significantly better than 3720 to 1. For the asteroid belt in our Solar System – a collection of millions of rocky objects between the orbits of Mars and Jupiter – the individual asteroids are so far apart that the most dangerous thing about flying a spaceship through there is dying of boredom. You have to deliberately go out of your way to get a close look at one of them, and that’s exactly what NASA’s Lucy spacecraft did on April 21, flying close by the asteroid named “Donaldjohanson”.
Image: Asteroid Donaldjohanson up close. At about 8km long, the asteroid is larger than the camera’s field of view. Credit: NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab
Lucy is on a mission to study 8 different asteroids. While asteroid Donaldjohanson was not a primary science target for the mission, this flyby served as an excellent test of the spacecraft’s capabilities. The Lucy spacecraft is named after the Lucy fossil, a 3.6-million-year-old early humanoid from a family of common ancestry to modern humans known to walk upright on two feet. The fossil was discovered in Ethiopia by palaeontologist Donald Johanson in 1974 and was itself named for the song ‘Lucy in the Sky with Diamonds’. Interestingly, this is the second asteroid that Lucy has visited, the first one being asteroid Dinkinesh in 2023. Dinkinesh is the Ethiopian phrase for “you are marvellous” and was Johanson’s preferred name for the fossil.
Image: The Lucy fossil on display.
The Lucy spacecraft is a hugely ambitious mission. In the same way that the Lucy fossil is a time capsule revealing humanity’s past, the Lucy spacecraft has the potential to reveal secrets to the origin of our Solar System, our planet, and even us.
Scientists think that the planets in the Solar System formed by a process of accretion. Basically, from little things big things grow. Pieces of dust stick together to make pebbles, pebbles stick together to make rocks, rocks stick together to make bigger rocks and so on until they are the size of planets.
The asteroids in our solar system are leftover remnants of this process from more than 4.5 billion years ago when the planets were taking shape. But there’s a problem. Planets and asteroids have changed a lot since they were new. On Earth we have weather and geology that long ago buried and blew away any clues to how our planet formed. Asteroids themselves frequently collide with each other, losing their original information.
Except for a few near Jupiter.
Image: The Trojan and Greek asteroids (green) near Jupiter are time capsules to the history of the Solar System.
Jupiter’s enormous size has allowed it to ‘bully’ the asteroid belt, and along the way it captured a few asteroids – the Trojans and Greeks, collectively called “the Trojans” – knocking them into a special orbit called a Lagrange point. These asteroids share Jupiter’s orbit away from the main belt.
Because of the way gravity works, asteroids in these Lagrange points are stuck there forever. They can’t escape or interact with the rest of the Solar System, and they have been stuck there in cold storage ever since Jupiter first formed more than 4.5 billion years ago. This means they are older than Earth. They are time capsules to the beginnings of our Solar System. They contain answers to what the Solar System looked like when it was forming, how minerals were distributed, and maybe even the molecules that later formed life on Earth. Visiting them to find out what they are made of and how they behave will give us clues to how life formed on our planet and how Earth got to be the way that it is today.
Where the Lucy fossil lit the candle on humankind’s past, the Lucy spacecraft will do the same on a much grander scale with the spacecraft visiting six Trojan asteroids over the next eight years. Interestingly, asteroid Donaldjohanson is not a Trojan asteroid, but it was close enough to Lucy’s flight path for it to take a look, and so it did.
Image: Lucy’s flight path will take it to visit six Trojan asteroids by 2033.
It is once again worth pointing out that over this twelve-year journey, Lucy is crossing the main asteroid belt several times as well as passing through both clusters of Trojan asteroids, yet it will only get close enough to 8 asteroids to study in detail. Asteroids are really, really far apart. Rather than needing the Millenium Falcon to dodge them, you need Lucy to actually get close to them. Lucy’s next asteroid encounter – the first Trojan asteroid it meets – will be asteroid Eurybates on August 12, 2027.
Until then, scientists will be keenly studying the information Lucy collected about Donaldjohanson to confirm that the spacecraft is working properly.
Does anybody else have Lucy in the Sky with Diamonds going through their head right now?
