July 2024
The Sky Tonight - July 2024
July continues the season of Makuru, keeping the cold weather going. This is the best time of year to simply go outside and …
ExploreNew Moon
August 4
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The casual observer
August brings us into the season of Djilba, a time of change. The very welcome rainy days will continue, but we should start seeing some clear days as time goes on, making for great stargazing.
The Milky Way is still in prime position above during the evening. Sagittarius and Scorpius mark the centre of the bright star fields with Antares a useful reference point. Now is a great time to see if you can spot the Sagittarius Teapot asterism. By imagining steam boiling out of the spout of the teapot you can locate the centre of the galaxy.
Image: Sagittarius and the Teapot (Green), along with Scorpius, locate the centre of the Milky Way.
Credit: Stellarium
Meanwhile in the north, Hercules, Boötes and Virgo draw the eye, with the distinctive stars Arcturus and Spica to help you find the way.
Image: The constellations low in the north during August.
Credit: Stellarium
Venus returns to the evening sky in the west, staking its claim as the evening ‘star’ and Saturn is visible in the east at a reasonable time of night, getting better as the month goes on.
A New Star
Keep your eyes out for the potential appearance of a new star. Sort of.
The star T Corona Borealis is a faint star, far too dim to be seen with the naked eye. Located in the constellation of Corona Borealis, every 80 years or so this usually unremarkable star suddenly increases in brightness enormously, about 1500 times. When this happens, the star becomes bright enough to be seen with the naked eye and suddenly appears as a ‘new star’ in the sky. It did this is in 1866 and 1946 and you can do the maths to determine that we are due for another event soon.
Interestingly, in these past events, the star was observed to get slightly brighter around 10 years before erupting, and then get slightly dimmer about 1 year before the main event. Well, in 2015 the star got brighter, and in 2023 it got dimmer again, so astronomers are eagerly expecting its imminent showcase sometime before or around September 2024.
Image: Light curve of T Corona Borealis during its last eruption in 1946.
Credit: PopePompus, CC BY-SA 4.0,
What’s actually going on is that T Corona Borealis is a binary system consisting of a white dwarf star and a red giant star. The smaller, but more massive, white dwarf star pulls material off the larger but less massive red giant star which accumulates on the surface of the dwarf star.
Image: Artist impression of a white dwarf-red giant accretion binary.
Credit: NASA
When enough material accumulates on the white dwarf, a temporary furious burst of nuclear fusion occurs, and the material erupts violently. This explosion makes the star bright enough to be seen at nighttime with the naked eye.
Keep your eye out!
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 06:25 AM | 10° above SSW | 34° | 10° above ENE | -2.3 | 6 min |
| 5 Aug 06:24 AM | 10° above SW | 69° | 10° above NE | -3.7 | 6 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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Mercury, Moon and Venus in the western sky just after sunset
August 6
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Moon near Antares
August 14
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Jupiter and Mars extremely close in the morning sky.
August 15
Planets to look for
Saturn is out in the east at a somewhat reasonable time, rising about 8pm but best viewed later in the evening.
Venus is visible in the west in the evening sky and is getting higher as the month goes on. Mercury is also there for the first couple of weeks of the month, but soon disappears in the Sun’s glare again. Both planets are joined by the Waxing Crescent Moon on Aug 6 for a nice display.
Image: Mercury, Venus and the Moon on August 6.
Credit: Stellarium
Jupiter and Mars make for great viewing in the eastern sky before sunrise. Jupiter is racing higher in the sky while Mars continues to just kind of hang there, so Jupiter overtakes it with a close approach on the 14/15th, the two planets separated by less than 1/3rd of a degree in the sky on these dates. The planets are backdropped by Taurus and friends, making for great viewing.
Image: Jupiter and Mars on the morning of Aug 15, backdropped by Taurus and the Pleiades (upper left)
Credit: Stellarium
Constellation of the month
Corona Borealis – The Northern Crown
Corona Borealis is a small constellation visible low in the northern sky during August. It is best spotted by looking for a very distinctive semicircular pattern made of seven stars, perhaps resembling a crown!
Image: Artistic representation of Corona Borealis with Alphecca identified.
Credit: Stellarium
The brightest star in the constellation, Alphecca, meaning “the bright star”, is a magnitude 2.2 eclipsing binary – two stars orbiting around one another that eclipse each other with a 17 day period when viewed from our line of sight.
The constellation is usually interpreted as the crown given by Dionysus to the Cretan princess Ariadne, daughter of King Minos of Crete. The princess helped Theseus escape from the half bull, half human Minotaur (Mino = Minos, Taur = Bull) before being abandoned by him and meeting Dionysus on the rebound. The Ariane family of rockets developed by the European Space Agency is named after Ariadne.
The constellation is home to T Corona Borealis, expected to go nova in the imminent future.
Object for the small telescope
T Corona Borealis – Maybe
If all goes ‘well’, T Corona Borealis will soon erupt in a display of spectacular violence, fusing millions of tons of hydrogen into helium and greatly increasing in brightness. Be sure to keep an eye on the news because it is only expected to be bright enough to see for a few days.
Image: Location of T Corona Borealis circled
Credit: Stellarium
The Polar Satellite Launch Vehicle on display at Scitech
You probably remember seeing this thing in the news when it washed up on the beach in Green Head in July 2023.
Image: Mysterious object from the beach
Credit: Wyper/Scitech
It caused international headlines when it first appeared and now it is being prepared for display at Scitech.
This object is the fuel tank of the third stage of a Polar Satellite Launch Vehicle (PSLV), a rocket built and operated by the Indian Space Research Organisation (ISRO). There have been 60 PSLV rockets launched since 1993 (as of this writing), and it is mainly used to launch Earth science satellites into Low Earth Orbit, though occasionally it has taken on more exotic missions, including launching the Mars Orbiter Mission, the Aditya L-1 solar observatory and numerous small satellites on rideshare missions.
Like any orbital class rocket, the PSLV is designed to discard empty fuel tanks and engine stages as it launches, a process called ‘stage separation’. The third stage shown here ignites after the second stage is detached, about 5 minutes after liftoff, and burns through 7 tonnes of fuel in 2 minutes to push the fourth stage and satellite cargo into space and almost to orbital speed, before detaching and falling several hundred km back down to Earth.
Image: The location of the 3rd stage, shown in orange, in the full PLSV stack.
Credit: ISRO, Scitech
Unfortunately, we don’t know exactly which PSLV launch this piece is from, so it is difficult to know exactly how it got here, however we can make some educated guesses. Many launches of the PSLV place satellites into a special type of orbit called a Sun Synchronous Orbit (SSO). To achieve this orbit, the PSLV launches from the Satish Dhawan Space Centre on the southeast coast of India, before turning sharply to the southwest at an angle about 97 degrees with the equator.
Image: Launch profile of a Sun Synchronous Orbit from India.
Credit: Google Earth, Spaceflight 101
This fuel-inefficient trajectory is to avoid dropping empty rocket stages onto Sri Lanka. Sun Synchronous Orbits are highly useful because a satellite following this trajectory will always pass over the same point on Earth at the same time every day (e.g. over Perth at 10am every day). This is very handy because if you want to look at (say) temperature data, you can’t compare today’s temperature at 9am with yesterday’s temperature at 4pm, because the time of day makes a difference. Having data collected at the same time every day is very useful.
Looking at this launch profile, we can deduce that the third stage of the PSLV often ends up splashing down in the Indian Ocean, if it doesn’t disintegrate on re-entry, and speculate that the piece we have might have been from a PSLV launch to SSO. This particular piece was heavily damaged during its journey, losing the engine nozzle and part of the tank lining, and the amount of barnacle growth on suggests it might have been at sea for some years before finally washing up in Western Australia.
Image: Scitech staff loading the object ready for transport
Credit: Wyper/Scitech
Image: Preparing the object for display
Credit: Wyper/Scitech
After being inspected by the Australian Space Agency for identification and safety analysis, the object was loaded into a truck by Scitech staff and transported to Perth where it was cleaned and presented for display.
The exhibit will be launching (ha!) on August 12 as part of National Science Week activities.
Meanwhile in the Scitech Planetarium
We’ve tallied the numbers. The 23/24 FY was the busiest year in history for us. We presented 2348 shows to 171,713 people. Thank you for coming everybody, you make our world turn!
