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May – Saturn at it’s best

Saturn at its best

The skies of May give us an increasingly better view of the winter Milky Way, our galaxy, spreading itself over the entire sky from west to east. The bright ‘starclouds’ are rising in the east as the sky becomes fully dark, and are best seen away from city streetlights, giving us an advantage over people living in Canberra.

These clouds are not clouds at all; if you look at them through a pair of binoculars, you will see that they resolve into countless thousands of individual distant stars. If you look at the brightest of these ‘clouds’, you will be looking towards the centre of our galaxy.

Bright stars in May include white Sirius low in the west (the brightest star in the whole sky), blue-white Canopus low in the south west, yellow Alpha Centauri (the closest star to the Sun) high overhead, orange Arcturus low in the north east, white Spica higher up, and red Antares (close to Saturn) in the east.

The planets in May: Saturn, Venus and Jupiter shine

On the 23rd May, the ringed planet Saturn will be seen at its best for 2015. Although visible each and every night, the 23rd is important as it is Saturn’s date of ‘opposition’, the day on which it lies exactly opposite the Sun in our skies. This means it is at its closest and brightest for the year, and rises exactly at sunset and sets exactly at sunrise.

Every planet that is further from the Sun than Earth has an ‘opposition’ every year, Saturn’s turn happens this month.

Saturn lies in the constellation Scorpius and appears close to the red supergiant star Antares. As Saturn is fairly bright, it is easy to spot and has a golden yellow colour which contrasts strongly with the red colour of Antares. Look out for both these objects, low in the east after sunset.

Saturn is famous for having a magnificent system of rings, the only such example in the Solar System. They are thought to have been created when a small moon of Saturn approached too close to the giant planet many tens of millions of years ago, and was ripped apart, creating a swarm of orbiting debris which spread out to form the rings.

This debris is slowly raining down onto Saturn’s upper atmosphere, creating a constant storm of shooting stars. One day, millons of years hence, all the debris will have rained down and the rings will be gone. As such, they are a temporary feature.

The rings are seen through even the smallest backyard telescope, and larger telescopes reveal gaps in the rings, the largest is as wide as the Atlantic Ocean and called the ‘Cassini Division’. Telescopes also reveal the shadows cast by both the planet and the rings, giving a very three-dimensional appearance.

Saturn is a gas giant, around 9 times the diameter of Earth, and is composed of hydrogen and helium gases with a small rocky core right in the middle. The combination of various gases give it a yellowish colour with hazy cloud features visible as bands. As a gas giant it has no solid surface, and any probe sent into Saturn would descend until being eventually crushed by the pressure.

Saturn has no less than 62 moons, of which four are most easily seen through backyard telescopes. Larger telescopes can see up to seven. If you have a telescope at home, take this opportunity to see Saturn for yourself, you’ll never forget the first time you see it.

Other planets visible in May include the giant planet Jupiter, visible as a bright yellowish star in the north west after sunset. It is unmistakable as the brightest object in that part of the sky.

Venus is also visible as a very bright white star low in the west after sunset. It is also unmistakable and will be described in more detail later.

In May, the moon is full on the 5th May, at last quarter (half) phase on the 12th, new on the 18th and at first quarter phase on the 26th.

By Dr David Weldrake

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