Observations

May 2018 night sky guide and sky chart

To help you learn about the southern night sky, Sydney Observatory provides a guide and a sky map or chart each month. This month’s guide is presented by Melissa Hulbert, Sydney Observatory’s Astronomy Programs Coordinator.

In the May sky guide, as well as showing us where to find the constellations Orion, Scorpius, Centaurus and Crux, and the star clusters, the Jewel Box, M6 and M7, Melissa tells us the best times to see the five planets visible with the unaided eye: Mercury, Venus, Jupiter, Mars and Saturn and the best time to see the Eta-Aquarid meteor shower.

Listen to the Audio
You can subscribe to the podcast on iTunes or directly download this month’s guide to your favourite audio listening device.

See the Sky Chart
We provide a May 2018 night sky chart (PDF) which shows the stars, constellations and planets visible in the night sky from anywhere in Australia. To view PDF star charts you will need to download and install Adobe Acrobat Reader if it’s not on your computer already.

Read the Guide
Hello and welcome to the night sky guide for May. My name is Melissa Hulbert and I’m an Astronomy Programs Coordinator at Sydney Observatory.

Before we start our night sky tour, make sure you download the May sky map from our website. Click the Astronomy tab, and go to the Monthly sky guides section.

Armed with your sky map and a small torch with some red cellophane covering it, find a nice dark place away from the glare of the street lights and make sure you know your cardinal directions – north, south, east and west. Remember that the Sun rises in the east, moves through the northern sky during the day and sets in the west; or a small compass will also point you in the right direction. Pick a comfortable spot either on a rug or a deck chair that you can lay back in. Wait about 5-10 minutes and allow your eyes to adapt to the darkness.

Now turn towards the west. Low in the western sky is the familiar constellation of Orion, the Hunter. In Greek mythology, Orion was a hunter of great skill and boasted that he could kill all living animals. Gaea, the Earth goddess, was alarmed by his statement and fearing for all the animals on Earth she sent a scorpion to kill him. Orion was stung on the shoulder but was revived and placed in the stars along with the scorpion. This entire myth is played out in the stars each year. As Scorpius the Scorpion rises in the east, Orion sets in the west, defeated. When Scorpius sets in the west the healer Ophiuchus crushes the Scorpion into the Earth and revives Orion so he can rise in the east again. Orion appears in many cultures, even the ancient Egyptians saw Orion as Osiris, god of the underworld and of regeneration.

If you’re having difficultly picking out the Hunter then look for ‘The Saucepan’. This is a familiar group of stars for those of us in the southern hemisphere and is Orion’s belt and sword. Orion is now on his side as he sets below the western horizon.

Now turn to face the east and there is Scorpius rising in triumph as Orion sets defeated for another season.
The Scorpion is one of the easiest constellations to pick out as it is one of the few that does look like what it’s supposed to represent. It covers about 30 degrees in the sky. Working out degrees in the sky is quite easy. Hold your arm out towards the sky and make a fist. From one side of your fist to the other, this is 10 degrees. Hold your other arm out and spread your hand out as wide as you comfortably can (so the opposite of a fist), from your little finger to your thumb is 20 degrees. Put your hands side-by-side and you now have 30 degrees, the size the Scorpion covers in the sky. This does work for everyone, as your arm length is proportional to your hand size.

Now, look for the Scorpion’s heart, Antares, a red supergiant that is 400 times the diameter of our Sun. Antares means ‘rival of Mars’, and when they are close together in the sky they certainly do look very similar.

If you have a pair of binoculars, then near Antares is a small globular star cluster, M4, which is a group of old stars that lies about 7,000 light years away, making it one of the closest globular clusters to us. Below the sting of the Scorpion are two open star clusters, M7 and M6, which are also worth a look. See if you can see the butterfly in M6. These names I’m giving the clusters are catalogue names. M stands for Messier and is named after Charles Messier, an 18th century French comet chaser. He made a catalogue of 103 fuzzy objects that were not comets so that he didn’t waste his time looking at them. Other astronomers later added a few more objects to the catalogue bringing the total to 110.

Time to turn and look towards the south. High in the southern sky is the constellation Crux, better known to us as the Southern Cross. Crux is Latin for cross. The Southern Cross, like the Scorpion, is another constellation that does look like what it’s supposed to represent. It is surrounded on three sides by the constellation Centaurus, and the two brightest stars in Centaurus make up the Pointers which point to the Southern Cross and this is one way to check you have the right cross as there are many stars in the southern sky that look like crosses. During May the Pointers are to the east and slightly south of the Southern Cross.

The second brightest star in Crux is a marker for a wonderful binocular and telescope object. To find the 2nd brightest star, whose name is Mimosa, look for the star in Crux closest to the Pointers. Now just nearby – at about 7 o’clock if you imagine a clock face over Mimosa, is a wonderful open star cluster called the Jewel Box. It looks like a sideways ‘A’. In a telescope, wonderful colours can be seen with white stars and a red supergiant. Sometimes even green appears but of course there are no green stars – this is just an illusion. The famous 18th century astronomer John Herschel gave the cluster its name as he likened it to a piece of multi-coloured jewellery.

Crux sits within one of the arms of our Milky Way and if you are away from the city lights you will see this arm and notice a dark patch between the brightest and second brightest stars of this constellation. This dark patch is called the Coalsack and is a dark nebula – lots of gas and dust that are blocking out the background stars.
In the dreaming of the Indigenous people, the Coalsack formed the head of the Emu and if you follow the dark dust lanes of the Milky Way east towards the Scorpion, you will see the Emu’s body and legs. There are lots of stories about Crux and the Pointers. Some say that Crux is the Eagle’s foot and the Pointers are the throwing stick used to hunt with. Others see the Milky Way as a river with Crux as a fish or stingray and the Pointers as two white cockatoos sitting in a tree.

Centaurus is a mythical half-man, half-horse and in Greek mythology represented the scholarly centaur Chiron, who tutored many of the Greek gods and heroes. He was put among the stars after he was accidentally struck by a poisoned arrow fired by Hercules.
The brightest star in Centaurus is Alpha Centauri which is one of the Pointers. It is the Pointer which is more distant from the Southern Cross or the brighter of the two stars.
In telescopes, Alpha Centauri appears as two stars, and both these stars orbit around each other once every 80 years and are starting to move closer together; by 2037-2038 only medium aperture telescopes will be able to distinguish the two stars. There is also a third member of this group called Proxima Centauri and it is the closest star to us after our own Sun at about 4.2 light years away or 42 million million kilometres. It takes Proxima about one million years to orbit its two companions and it is a red dwarf star, making it a challenge to see – it is not even in the same field of view as its companions.

What else can we look forward to seeing in the sky in May 2018?

Venus is in the early evening sky after sunset. It spends most of May in the constellation Taurus moving in the last third of the month to Gemini. On the 21st, Venus will pass just to the north of M35, a beautiful star cluster visible to the unaided eye in dark skies. On the 17th, a thin crescent Moon is to the left (west) and slightly below the brightly shining planet.

High in the northeastern sky after sunset is Jupiter. It is easy to find as it is the brightest object in that area of the sky, sitting in the constellation Libra. Binoculars will show you the four largest moons known as the Galilean satellites and small aperture telescopes will show one or two of the Jovian clouds belts. On the 3rd and 4th, Jupiter will be close to the star Nu Librae. Nu Librae is an orange giant star about 765 light years away and although of similar brightness to the Galilean moons, with the star having a distinct orange colour and being south of the plane of the moons, there should be little confusion between them. On the 27th, the waxing gibbous Moon is to the left (north) of Jupiter while the following evening, the 28th, sees the Moon below the gas giant.

Rising later in the evening is the red planet, Mars. It spends the month equally in two constellations, Sagittarius and Capricornus. On the 6th, a waning gibbous Moon will be visible below and slightly to the left (west) of Mars and on the 7th, the Moon is slightly to the right (north) and below the red planet. On the 14th and 15th, Mars passes a mere half a degree (0.5°) from the compact globular star cluster M75. Shining at magnitude 8.5, in binoculars, M75 appears as a fuzzy round smudge though a large aperture telescope is required to resolve the stars within the cluster.
Martian equinox occurs on the 23rd which indicates the start of the southern spring and the northern autumn. Regular telescope observers of the red planet will see the southern polar cap start to emerge from the winter darkness. The southern polar cap is currently at its largest but with the onset of spring it will start to decrease in size.

Rising mid-evening in the east is the beautiful ringed-planet, Saturn. Saturn spends the month in Sagittarius, close to the well-known globular cluster M22, a wonderful sight in a telescope which resolves the stars within the cluster. Also visible in binoculars, M22 appears as a fuzzy smudge. Saturn’s impressive ring system can be seen in even small aperture telescopes and depending on the telescope you are using you may even catch a glimpse of a few of Saturn’s moons including the second largest in our Solar System, Titan. On the 4th, the waning gibbous Moon is above and slightly to the left (east) and on the 5th, the waning gibbous Moon is below and slightly to the right (south) of the ringed planet.

All of the early-birds have not been forgotten as May sees four planets in the morning sky.
Mercury is low in the eastern sky before twilight. On the 14th, a thin waning crescent Moon is to the right (east) of Mercury with Uranus about two degrees to the north (left). Binoculars will be needed to spot Uranus in the early morning twilight with the best viewing about 30minutes before the end of astronomical dawn which on the morning of the 14th ends at 5:43am EST.

The other morning planets are Jupiter, which will be in the western sky as dawn approaches and Mars and Saturn, both high in the north-western sky.

I do have one wildcard for you all this month which is the Eta-Aquarid meteor shower. This shower is linked to Halley’s Comet and is one of the most popular in the southern hemisphere. When comets pass by us and pass close to the Sun they leave a trail of small particles and dust behind. When the Earth passes through this trail we see lots of meteors appearing to come from the one area of the sky. This is called the radiant and each shower is named after the constellation or bright star near which the radiant appears. In this case it’s the constellation of Aquarius and the star is Eta Aquarii. The shower runs between the 19th April and the 28th May, with the peak on the morning of 6th May.
At its peak the rate will often be around 50 per hour. The Eta Aquarids are usually very swift and are a striking yellow colour. They are also known for their trains with about 25% of meteors leaving a train behind.
The best time to observe any meteor shower is after midnight, usually a few hours before dawn, so on the morning of the 6th, look towards the east. There will be a waning gibbous Moon in the early hours of the morning which may interfere with observations, however the brighter meteors should still be visible especially if you are away from city lights.
The Eta-Aquarids have a history of good performance. In 1975 there was an hourly rate of 95 and in 1980, an hourly rate of 110!

If you observe any of the planetary and lunar events or see the Eta Aquarids, we’d love to hear from you via our blog, Facebook or Twitter pages.

I leave you now with a quote from Stephen Hawking: ‘One of the basic rules of the universe is that nothing is perfect. Perfection simply doesn’t exist. Without imperfection, neither you nor I would exist.’

Wishing you clear skies and see you next month under the stars!

If you have enjoyed this monthly sky guide and think you might want to regularly check out what’s in the night sky, why not purchase a copy of Sydney Observatory’s book the ‘Australasian Sky Guide’ for 2018. It not only contains detailed monthly sky guides, but is packed with astronomical information including rise and set times for the Sun, Moon and planets, tides and a detailed look at our Solar System and upcoming astronomical events. Only $17 from Sydney Observatory and Powerhouse Museum shops or you can purchase it online (additional costs apply).
For more information on the night sky, check out our blogs on Sydney Observatory’s website. You can also check Sydney Observatory’s blog, Facebook page and Twitter account for the latest astronomical information.

This has been Melissa Hulbert from Sydney Observatory with the May sky guide podcast.

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