The May 2016 Night Sky

It’s the middle of May! Let’s go out tonight and look at the stars! At this time of year in the UK and Ireland, our nights are getting later and shorter, partly due to our planet’s axial tilt and partly due to daylight savings time, with the Sun setting soon after 11.00pm and rising at approximately 4.00am. Let’s wrap up and go at midnight on 16 May, as it will only get truly dark at that time.

 

The Odd Couple: giant Saturn and little dusty Mars together. (image credit: Colin Johnston/Armagh Planetarium/Stellarium)

The Odd Couple: giant Saturn and little dusty Mars together. (image credit: Colin Johnston/Armagh Planetarium/Stellarium)

 

There are two planets low in the south. One is the unmistakable red orange orb of Mars, a planet that has recently been invaded and occupied by robots. The other is pale yellow Saturn. The famous rings are well-positioned so do try to see them with any kind of binoculars or telescope.

Libra is also low in the south, just west of Virgo. The constellation Libra has been thought to represent a set of scales from as long ago as ancient Babylonian times. Some say this was because during the autumnal equinox back then when the days and nights were the same length (or “balanced” like scales) the Sun was in Libra. The ancient Greeks saw Libra as an extension of the constellation Scorpius (the Scorpion), representing the venomous arachnid’s claws. This is reflected by the names of the stars in Libra, their current names are Arabic translations of their Greek names. Libra is marked by the three brightest stars in the constellation, one of which has been said since ancient times to be a rare example of a green-coloured star. It is called Zubenelchemali (Beta Librae) which means “Northern Claw”. Here is your chance to prove your superiority over all those ancient civilisations! Look at Beta Librae, what colour does it look to you? Chances are it won’t be green!

Another star in Libra is called Zubenelgenubi (Alpha Librae) which means “Southern Claw” and is a multi-star system about 75 light years away. A pair of binoculars will show Alpha Librae as a pair of stars but there are at least two more in this star system. The third bright star is called Zubenelakrab (Gamma Librae) which means “Shears of the Scorpion.” The best-known star in Libra though cannot be seen without a major telescope. This is Gliese 581 a red dwarf about 20 light years away. It has a family of at least six planets some of which have potentially habitable surface temperatures.

 

image of Juno probe

Joy! Juno journeys to Jupiter (Image credit: NASA/JPL)

 

Looking westerly we can see giant Jupiter between Virgo and Leo. It’s unmissable. On 4 July 2016, NASA’s Juno mission arrives there in the form of a huge “Y”-shaped robotic spacecraft. Each arm of the Y is a 8.9m long solar array to power the probe from the faint rays of the distant Sun. The spacecraft will go into a polar orbit around the planet to study Jupiter’s composition, atmosphere, gravity field, magnetic field and magnetosphere in its polar regions.

Looking to our own planet’s northern polar region, as usual, the circumpolar constellations are still visible in the north (if they aren’t then tonight there is a really bad glitch in the Matrix), with Ursa Major, the Great Bear, directly overhead facing west, Draco the Dragon directly overhead facing north, and Ursa Minor the Little Bear just tucked in below Draco. Cepheus the King and the very faint Camelopardalis the Giraffe are midway up the sky in a northern direction and Cassiopeia the Queen, is low in the north. These constellations are always visible and appear to rotate around the star Polaris which marks the tail of the Little Bear.

 

Look north about mid night. (Image credit: Colin Johnston/Armagh Planetarium/Stellarium)

Look north about midnight. (Image credit: Colin Johnston/Armagh Planetarium/Stellarium)

 

Almost directly north is the familiar constellation Cassiopeia, then there is a little constellation just to the right of this celestial “W” which is sometimes called Little Cassiopeia because it looks like a smaller “w”. This is Lacerta, the Lizard, a simple constellation with no outstanding features. Does that sound unfair? Its stars aren’t particularly bright, all of 4th magnitude. There are no pretty Messier objects or fancy galaxies. Maybe it is up there to commemorate a thrilling story from mythology about a giant rampaging reptile? Alas no, there is not an interesting story behind Lacerta.  What a slacker! There is an open star cluster (or possibly not) called NGC 7243, just right of the central peak of the “w”, and Lacerta is home to the “weird, warm and fuzzy” exoplanet HAT-P-1b (which cannot be directly observed) but these are about the only things of note. One night in 1687 Polish astronomer Johannes Hevelius (1611 –87) made up the constellation, just like that. Hevelius initially wanted to call it “Stellio” (the stellion). The what? Don’t worry. I had to look it up too, although a stellion may sound like what a posh English person would call a boy horse, a stellion is actually a member of a genus of common and spotty lizards. The spots remind some people of stars, so the little beasts are sometimes called “star lizards”.

The Summer Triangle has also just risen in the east. It will slowly make its way south over the next few months. The Summer Triangle is a pattern made up of three stars from three different constellations. These are brilliant blue-white Vega (Alpha Lyrae) in the constellation of Lyra the Harp, midway up the eastern sky; distant Deneb (Alpha Cygni) in the constellation Cygnus the Swan, half way up the ENE sky; and near neighbour Altair (Alpha Aquilae) in the constellation of Aquila the Eagle which is low in the eastern sky.

So that’s the May night sky. Make the most of it, because the nights are getting shorter and shorter!

 

(Article by Colin Johnston, Science Education Director)