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The night sky for August 2015

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during August 2015.

Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during August 2015.

The Planets

At the beginning of the month three bright planets appear low in the western evening sky soon after Sunset. Brilliant silvery Venus is the brightest and highest with golden Jupiter below and right. Mercury is well below the two bright planets on August 1st, but moves quickly up the sky, night to night, as Venus and Jupiter sink lower. On the 7th Mercury is just a full-moon's diameter to the right of Jupiter. Venus is left of the close pair of planets, and all three set about 70 minutes after the Sun.

After passing between us and the Sun mid-month, Venus will appear in the eastern dawn twilight. By August 20th it will be rising in the east an hour before the Sun. Venus will remain the 'morning star' for the rest of the year.

Mercury continues its ascent of the evening sky through August while Venus and Jupiter disappear in the twilight. By month's end Mercury is setting due west after 8 pm, making its best evening sky appearance of the year. The bright orange star Arcturus is setting in the northwest, well to the right of Mercury, often flashing red and green as it goes.

Saturn is the only bright planet in the late-evening sky. A small telescope shows Saturn's ring system and biggest moon, Titan, looking like a star about four ring-diameters from the planet. More powerful telescopes should reveal faint banding in the planets atmosphere along with gaps and variation in colour of the rings.

The Stars

In the north, to the left side of the Milky Way is Vega, the fifth brightest star in the sky, which forms part of the constellation of Lyra that represents an ancient stringed instrument. Opposite Vega, in the south, Canopus is the second brightest star in the night sky and twinkles with a yellow tint. To the Polynesians this star is Atutahi, the navigator, considered by Māori as the chief of all the stars in the sky. Canopus was also the navigator of Argo Navis, the ship in which the argonauts searched for the Golden Fleece. Argo Navis, once the biggest constellation in the sky, was subdivided into Carina (the keel, or the hull, of the ship), Puppis (the poop deck, or stern), and Vela (the sails). These constellations now hold the asterisms known as the false and diamond crosses which are adjacent to Crux, the Southern Cross.

Above Crux are Alpha Centauri, the third brightest star, and Beta Centauri, the 11th brightest star in our night sky, which point you towards the Southern Cross and appear to follow it around the sky. To the north of Beta Centuri lies the brightest globular cluster, Omega Centuri, which can be seen as a fuzzy star. With a small telescope the cluster becomes a glowing, shimmering ball of stars, with many individual stars visible towards the outskirts of the cluster.

Sitting about half way above the southern horizon as the Southern Cross sinks towards its lowest position in the sky is the faint constellation of Tucana, the Toucan. Alpha Tucanae is a magnitude +2.8 star about 200 light years away. Beta Tucanae is a loose group of 6 gravitationally bound stars approximately 140 light years away. The two exceptional objects in the Toucan are the Small Magellanic Cloud (SMC) and 47 Tucanae the second brightest globular cluster in our sky.

The SMC is a dwarf galaxy visible to the unaided eye as a cloudy smudge in the sky. The secret to viewing it properly is to use peripheral vision to bring out more detail. Peripheral vision is a trick that visual astronomers use to spot very faint objects such as nebulae, clusters or galaxies. Try to look at the object with the tip of the eye rather than directly at it, as if you are looking just to side of it, and you should be able to see much more. The Small Magellanic Cloud is best viewed from a dark location and it is bright enough to be seen from many suburban locations as long as the Moon and local lighting are not too bright.

There is another larger and brighter cloud to the right of the SMC. This is the Large Magellanic Cloud, another of our galactic neighbours lying just 160,000 light years away. The Magellanic Clouds, the crosses, alpha and beta centauri and all the beautiful clusters in the south are objects that can always be seen in our southern night sky as they are circumpolar, meaning they never set below our horizon.

A Final Note From Claire...

Thank you for listening to the August jodcast. I will shortly be heading off on maternity leave so our new Curator of Science, Haritina Mogosanu will be stepping in to produce the Southern skies section over the next few months. I look forward to catching up with you all again when I return in the New Year.

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The Night Sky This Month is one part of the Jodcast. The full show contains the latest news, interviews with astronomers, answers to listener questions and more.

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