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
Don’t miss Stargazing Live on ABC TV during the first week of April. From 4th-6th April Dr Brian Cox is here in Australia to present a series of live tv shows about the night sky. You can get involved, too, and enjoy lots of pretty pictures and time-lapse sequences of the sky at www.abc.net.au/tv/programs/stargazing-live/.
Orion seems to linger in the west at this time of year. It seems to hang about out there for several months! What’s happening? Shouldn’t it be setting a little earlier each night? Well, it is, but twilight is also ending a little earlier each night too as we head into winter. The combined effect makes Orion seem to hang about for longer than usual.
The second half of April is a good time for a spot of meteor watching. While the hours between midnight and sunrise are the best time to be seeing meteors there is a meteor shower active in the evening at this time of year. Known as the Virginids, as they originate from the constellation of Virgo, they can sometimes produce long green-coloured fireballs in the evening sky. This is one shower you don’t have to stay up late for.
Dates of interest
8th – Jupiter at opposition
10th - Moon to the left of Jupiter, evening sky.
12th – Yuri’s Night
16th – Moon to the left of Saturn, late evening sky.
24th – Thin crescent Moon to the right of Venus, morning sky
28th – Moon the left of Mars, low in the evening twilight.
Planets to look for
As the Sun sets during April, it takes Mars with it. The red planet is now around the far side of the Sun from Earth and is a distance small dot in telescopes. It’s time to be patient while it disappears from view for a while – winter 2018 it will be behind us once again and the view will be the best since 2003.
Turn eastwards to look at Jupiter instead. It’s at opposition on the 8th of April, which means it’s opposite the Sun from the Earth and the best viewing of the planet is to be had. On the evenings of April 6th and April 13th you might see a small black dot moving across the north polar cap of Jupiter; these are transits of the shadow cast by its moon Europa. The Full Moon joins it near the bright star Spica in Virgo on the 10th and 11th. Jupiter will be in between Spica and the Moon, and you should be able to see a slight colour difference between the whiteness of Spica and creamy-yellow of Jupiter. Jupiter will also be brighter than Spica.
Saturn rises around 9.30pm now. It’s moved down near the teapot asterism in Sagittarius. Jupiter is slowly catching up to Saturn for a once in twenty year conjunction that occur in 2020 – only a few years away! It means a late evening during April if you want to enjoy the rings of Saturn before you head to bed as well, but in a month or so we will have both big planets up high in the early evening sky to view.
Venus soars back into the morning sky after its inferior conjunction with the Sun last month. It will stay there until the end of August. Mercury is the last planet to mention, but this month it is largely out of sight, too close to the Sun to be seen. During May it will make a nice appearance in the morning sky, so if you’d like to see it you are probably best waiting until then.
Constellation of the month
Cancer the Crab
Cancer is said to represent a crab who was annoying Hercules while he tried to slay the nine-headed Hydra. Hercules crushed him underfoot in the fight and Hera, always liking someone who had a go at Hercules, placed him in the sky. This seems a rather weak reason for Cancer’s place amongst the stars but we may never know why as Cancer’s origins are far older than the Greeks’ naming of it, a common occurrence in star lore. (Cancer is not named after a disease, but the Latin name for Crab. Early doctors thought that cancers looked crab-like and that is how they became known as such.)
The Tropic of Cancer, running along latitude 23.50 north, is a relic from two thousand years ago, when the Sun reached its most northerly point in the sky in this constellation. If we were to name the Tropic line today it would be the Tropic of Gemini, due to the effects of precession.
Cancer doesn’t have many bright stars in it, so you find it either by locating Gemini to the west and Leo to the east and looking in between them, or looking for the Beehive Cluster that sits in the middle of it. The Beehive Cluster (Messier 44) is still marked as Praesepe on most star charts. Praesepe means the Manger, and the two bright stars either side of it are known as the Northern Donkey (Asellus Borealis) and the Southern Donkey (Asellus Australis).
Rho Cancri, better known by its Flamsteed number 55 Cancri, but now also known as Copernicus as renamed in the first round of renaming of stars with exoplanets, is a double star that has five exoplanets circling around it. The last planet found orbits within what is sometimes called the “Goldilocks Zone”, the zone where is the planet is the right distance from its star (that is, not too close and not too far) for liquid water to be found. But since the planet itself seems to be a gas giant, we will have to search for water on any moons found circling it.
Cancer occupies an area of relatively faint stars between Gemini and Leo.
Objects for the small telescope
The Beehive Cluster
The Beehive cluster is a large open cluster of stars found in the middle of the constellation of Cancer the Crab. An open cluster is a group of stars that all formed out of the same cloud of dust and gas. In a dark sky you can see this cluster without the aid of binoculars or telescope, but in the city you may need some help. Locate Gemini to the west and then Leo to the east and roughly halfway in between is the Beehive cluster.
The Beehive stands out well at low power (it actually looks best in binoculars). You should be able to spot a square house with a triangular roof, much like a stick-figure drawing of a house, which is the hive and the hovering bees are the surrounding stars. This cluster lies about 520 light years away.
Help Find Planet 9
Here’s an astronomical citizen science project for you to get involved with on a rainy night. Astronomers believe there is a large planet about ten times the size of Earth lurking in the outer solar system and they would like your help to find it. They would rather ask people to help than machines, as people are much better than computers at pattern recognition.
Astronomers have gradually narrowed down the area where Planet 9 is currently thought to be by confirming where it definitely isn’t and they think that is in the area of the constellation Cetus the Whale. This lies on the celestial equator, so both northern and southern hemispheres can see it. The images used for the Zooniverse project come from the Skymapper telescope at Siding Spring Observatory in Coonabarabran, NSW. It’s still a very large area to find a very small, distant object so there is a lot of sky to be searched.
Once you sign in to the project site there is a very brief two page tutorial that shows you how to look for the out-of-place colour spots that indicate a moving object on the image, and away you go! It’s very easy.
If you’re lucky enough to be one to find Planet 9, you will be invited to help name it. At worst, you might just find another plain old asteroid, in which case you still should get to help name it!
If you get really keen and want some more citizen science to do, check out the other projects Zooniverse runs; you could decipher old ships logs for climate records, or handwritten notes and diaries from the Anzacs at Gallipoli, or even help to identify animals on night video taken by the Western Shield camera watch here in the jarrah forest of Western Australia.
The direct link to the Planet 9 project is www.zooniverse.org/projects/skymap/planet-9.
For more background on the history of the search for Planet nine the Wikipedia page has the clearest description I’ve seen: en.wikipedia.org/wiki/Planet_Nine.