The Sky Tonight is a monthly update of the amazing things you can find when looking up from here in Western Australia. This section is written by Jacquie Milner, resident astronomer at the Scitech Planetarium.
The casual observer
The Cassini mission at Saturn will end this September when the bus-sized spacecraft is deliberately crashed into Saturn so it won’t accidently contaminate any of Saturn’s moons. Each week leading up the final plunge Cassini will orbit Saturn between the planet and the rings, an area that has previously been considered so dangerous it was only traversed during the initial aero-braking manoeuvre when Cassini first arrived at Saturn in 2005. Cassini has sent us thousands of stunning pictures since then, but the first dive last week promises the best may be yet to come. We’ll follow up on Cassini’s success in September but for now make sure you check out the short video NASA have released as a promotion to this Grand Finale.
Now is good time to see meteors, with the Eta Aquarid meteor shower active during the early hours of the morning in the first week of May. Even if you don’t want to be up in the cold morning hours to see this major shower, keep looking up during the evenings, as there are a couple of smaller meteor showers active just after sunset at this time of year.
Dates of interest
4th – Moon next to Regulus, brightest star in Leo, evening sky
7th – Moon to the left of Jupiter, evening sky
8th – Full Moon to the right of Jupiter, evening sky
13th – Moon to the left of Saturn, evening sky
23rd – Moon next to Venus, morning sky
24th – Moon above Mercury, morning twilight
Planets to look for
This is your last chance to see Mars in the evening sky for 2017 – but be prepared for some disappointment. It is on the far side of the Sun and will just be a small coloured dot in your telescope. Some patience will be required, unfortunately; this time next year we will be watching it grow bigger and bigger as the best opposition since 2003 approaches!
But now both Jupiter and Saturn are in the evening sky! Jupiter is already well up as darkness falls. It is still in Virgo, and on the 8th the Full Moon will make a triangle with Jupiter and the star Spica in Virgo (see the image below).
Saturn begins the month rising around 8pm but by the end of May will be rising as the twilight ends at 6pm, so you will be able to observe it most of the evening. It will be at opposition next month, so it is also coming up to the best time of year to view it and its moons.
Both Venus and Mercury will be visible every morning during May. Bright Venus will rise first, around 3.30am. The Moon will be close to it on the morning of the 23rd, which should be a pretty sight for those out and about in the pre-dawn hours that day. Mercury rises about 5am and around mid-month is a good half an hour ahead of the morning twilight. The morning after the Moon poses with Venus, it hovers over Mercury, helping you to identify this elusive planet. Make the most of it, as Mercury will be out of sight for most of June.
Constellation of the month
Corvus the Crow
Corvus is a small but prominent constellation to the south of Virgo in the sky. He is connected by story to the nearby constellations of Hydra the Water Snake and Crater the Cup. The story form Greek mythology tells of how Apollo asked Corvus to fetch him some water in his Cup. Corvus did this but on the way back he was distracted by some sweet ripe figs. Much later Corvus realised how long he had taken on his errand and snatched up a snake (Hydra) in his claws as an excuse for the delay. Apollo did not believe his excuse and punished the crow by denying him a drink from the cup leaving him thirsty, which is why we still hear them croaking today.
The body of Corvus makes a 'baseball diamond' shape in the sky, with two stubby wings to the north and south. Watch for him flying overhead in the evening sky during the winter months.
If you can see Jupiter in Virgo, look above for the diamond shape of Corvus the Crow.
Objects for the small telescope
The Emu in the Sky
This object doesn’t need a telescope, just your eyes! The Emu is made up of the dark dust lanes in the Milky Way during the colder months of the year and is one of the few Indigenous pieces of star lore that is common across southern Australia.
If you are in a dark location on a moonless night and can see the Milky Way, look to the lower left of the Southern Cross for the large dark nebula known as the Coal Sack. This is a large cloud of cold dust blocking out the stars behind it in the Milky Way. This odd blob also marks the head of the Emu. Follow the neck of the Emu down past the Pointers, alpha and beta Centauri, then the back of Emu is where the central bulge of the Milky Way spreads out near Scorpius.
Autumn is a good time to catch the Emu in the early evening sky. When the full Emu is sitting on the eastern horizon in the early evening, around May, the emus have usually finished their laying and it was time to go and collect some emu eggs.
If you can see the Milky Way, look for the Emu in the sky, using the dark dust lanes in the Milky Way. It stretches from the Southern Cross to the central bulge in the star clouds of our galaxy.
Nine Facts about Comet Halley
Think of a comet and most people will think of Halley’s Comet, the first comet to be recognised as returning periodically. There are always a few comets travelling through the sky at any one time, but they are usually faint and hard to see, just little fuzzy balls that might only show up in images. Halley is one of the few we can rely on to be visible to the unaided eye. As the Earth passes through the debris stream of the comet during the first week of May, here are a few facts about the “first” comet.
1. The Chinese were the first to record a sighting of Comet Halley in 240BC, but it was likely to have been seen before that time as well.
2. Its appearance in 1066 was recorded on the Bayeux Tapestry, which depicts the story of the Norman conquest of England, ending in the Battle of Hastings.
3. The Earth actually passed through the comets tail during the 1910 return. Because it was known that there was the toxic gas cyanogen in the comet’s tail, a deadly gas to humans, some shysters took advantage of the fearful and sold useless gas masks, “anti-comet pills” or umbrellas to shield them from the gas. Others drowned in barrels of water trying to protect themselves. In reality nothing happened – we’re still here, aren’t we?!
4. Six space probes were sent out to meet Halley when it returned in 1985. The most famous of these was Giotto, from the European Space Agency, which returned images of what its nucleus looked like.
5. The nucleus of Halley is shaped like a peanut, and is 15 km long and 8 km wide. This doesn’t seem very big considering its tail of ice and dust can be millions of kilometres long when it is close to the Sun.
6. It takes 76 years to complete one orbit around the Sun. Currently it is at its furthest point from the Sun, known as aphelion. It won’t return to perihelion until 2061.
7. The Earth crosses the debris stream of Halley twice a year, when we experience two meteor showers, the Eta Aquarids in early May, and the Orionids in late October.
8. The 1986 apparition was the least favourable in recorded history, with the comet being on the far side of the Sun to the Earth. The next apparition will be the same.
9. No one actually knows the correct pronunciation of Halley’s name, so whether you want to say “Hail-ee” or “Hal-ley” you’ll be correct!
Halley’s Comet as depicted on the Bayeux Tapestry.