July 2025
The Sky Tonight - July 2025
July continues the season of Makuru and with it continues the fantastic, cool weather. Ironically, this is the best and worst …
ExploreFirst Quarter
August 1
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The casual observer
August brings us into the season of Djilba. This is a transitional period where winter continues but eventually gives way to new growth.
The Milky Way continues to dominate the night sky no matter where you look. The further you can get away from any lights, the better. Look to Scorpius and Sagittarius to identify the middle of the galaxy with its bright star fields.
Image: Scorpius and Sagittarius mark the centre of the Milky Way. Credit: Stellarium
Facing east, Venus and Jupiter put on a show in the morning skies. All month, Venus seems to hang above the horizon, while Jupiter rises higher in the sky day by day to greet it. On the mornings of August 12 and 13 they will be within 1 degree of each other, less than the width of your thumbnail at arms length, but you can still go and look at them any day this month. Venus is the brighter one in these views.
Image: Venus and Jupiter at closest approach as seen on August 12. Credit: Stellarium
You might see things about the Perseid meteor shower in your news feeds this month. Unfortunately, we can’t really see much of this shower from Australia. If you live right up north or in the Top End you might see some meteors low on the northern horizon on the mornings of August 12/13. From Perth, you’re better off looking at Venus and Jupiter instead.
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 |
| 3 Aug 06:11 AM | 10° above SW | 53° | 10° above ENE | -3.1 | 6.5 min |
| 6 Aug 05:25 AM | 77° above NNE | 77° | 10° above NE | -3.8 | 3 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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Closest encounter of Venus and Jupiter
August 12
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19th anniversary of Pluto being reclassified as a Dwarf Planet
August 24
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Moon close to Mars
August 28
Planets to look for
Venus and Jupiter dominate the eastern morning sky this month. Keep your eye out for the close encounter on August 12/13. They are joined by Mercury low in the sky in the second half of the month.
Mars is there in the northwest after sunset, though it’s not very bright. It will continue to hang there for the next couple of months. Saturn is rising in the east at about 8:30pm this month so if you’re up a bit later its yellowish tinge will make for a good sight in the northeastern sky.
Constellation of the month
Norma – The Set Square
Norma is a small constellation in the southern sky and is often represented as a set square or carpenter’s square. The constellation was named by Nicolas-Loius de Lacaille, that powerhouse of constellation mappers who named 13 more constellations in addition to Norma. All of these were named after tools of the Age of Enlightenment.
Image: Norma, the set square, with Scorpius and Centaurus for reference. Credit: Stellarium
Norma straddles part of the Milky Way – the Norma Arm as it is called – so contains fields of countless millions of stars and also allows views outside our galaxy to the distant universe, all while being quite faint. Gamma Norma – the brightest star in the constellation – comes in at only a measly magnitude 4 and everything else in the constellation is fainter than that.
Offering a view to the distant universe, Norma contains many deep sky objects. Perhaps most visually striking is the Jellyfish Galaxy in the Norma Cluster. This galaxy is moving through a particularly dense galaxy cluster and the surrounding resistance of intergalactic gas strips material from the galaxy into a long tail. The analogy is like putting your head in front of a pedestal fan and letting it blow your hair back behind you.
Image: The Jellyfish Galaxy. Credit: ESA/Hubble, CC BY 4.0.
Astronmers studying distant galaxies in the constellation of Norma noticed that – after accounting for the movement of the galaxies caused by the expanding universe – the galaxies were all still moving in the same direction towards… something. That something is now called the ‘Great Attractor’, whose gravity dominates the nearby universe in this direction. Unfortunately, the Great Attractor lies directly in the line of sight of the Milky Way, so is obscured by the stars and gas in our own galaxy. Further study has lead to the conclusion that the Great Attractor is the central point of an even larger supercluster of galaxies called Laniakea, of which the Milky Way is part.
Video: The Great Attractor and Laniakea Supercluster. Credit: naturevideo
Object for the small telescope
Venus and Jupiter
The close encounter of Venus and Jupiter on the morning of August 12 makes for excellent viewing in even a low powered telescope. You may even be able to resolve some of Jupiter’s moons or the phase of Venus.
Image: Jupiter and the location of the Galilean moons on August 12. Credit: Stellarium.
Image: The phase of Venus on August 12. Credit: Stellarium.
The Companion of Betelgeuse Revealed
“Astronomers find a new star!” might not sound like the most exciting headline ever but trust me on this one.
We all know about Betelgeuse, the red supergiant star in the constellation of Orion.
Image: Betelgeuse in Orion. Credit: Stellarium.
At about 11 million years old and 16 times heavier than the Sun, Betelgeuse is the closest red supergiant star to us, a staggering 700 times larger than the Sun. Put another way, if you replaced the Sun with Betelgeuse, the outer edges of the star would reach all the way past Jupiter.
Image: The Solar System with the Sun replaced by Betelgeuse. Credit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella
Betelgeuse is a variable star, which is to say its brightness changes over time. The star gets brighter and darker every 400 days or so as the star grows and shrinks – think of it a bit like breathing. Variable stars are quite common, with various physical mechanisms explaining their changing brightness.
Image: The variable brightness of Betelgeuse including the ‘Great Dimming‘ of 2019/20. Credit: Pilate et. al 2024, CC BY 4.0.
But there seems to be another more subtle change in brightness of Betelgeuse every 6 years, and astronomers just couldn’t find an explanation that properly described it. Some scientists speculated this was caused by a companion star on a six-year orbit stirring up Betelgeuse’s outer atmosphere. This would match the data. It’s a nice idea, but a good hypothesis has to hold up to observational fact.
Because Betelgeuse has such a detailed observational history, astronomers were able to make highly detailed predictions about the orbit of this hypothetical companion star. They predicted that if this star existed, it would be furthest from Betelgeuse (and thus the easiest to see) on 18 December 2024. So, scientists used the ‘Alopeke instrument on the Gemini North telescope in Hawaii to look for it.
Image: The Gemini North observatory houses the ‘Alopeke instrument. Credit: Noirlab
Atmospheric turbulence is the bane of all ground-based astronomy, causing stars to ‘twinkle’. While somewhat pleasant for amateur stargazing, for professional astronomers this means that pictures of stars tend to ‘smear out’, making it very difficult to focus on small targets like stars in great detail.
The ‘Alopeke instrument takes a novel approach to this problem. Instead of taking long exposure pictures – during which time the turbulence in the atmosphere smears out stars – it takes hundred of pictures per second, each exposure only a few milliseconds long. This essentially ‘freezes out’ any atmospheric distortion, which can be accounted for later, without smearing the image of the star. In the end, the astronomers took 6000 pictures of Betelgeuse in this way. And what was the result?
Image: Betelgeuse’s companion star (blue, lower left) and Betelgeuse (orange, centre). Credit: Howell et. al 2025
This detection, if verified by future observations, is a stunning confirmation of the predictive power of good science. Analysing all the data takes considerable time, and by now the star is once again lost in the glare of Betelgeuse. According to orbit modelling, the next time to see the star will be in November 2027. There will be no shortage of astronomers ready to try and catch a glimpse of it.
