The August Night Sky

Welcome stargazers to that haven where in the midst of our busy lives, between all our comings and goings, we can look up and find solace, and be inspired by the quiet glittering beauties overhead. So let’s start with the summer triangle, discussed in July’s article, and use it as our springboard to leap across the dark sky to other constellations. Having located these 3 bright stars of the triangle, let’s fix our eyes on Altair, the lower-most of the 3. Approximately halfway down, towards the horizon from this star and a little to the right is a neat little pattern of stars known as Scutum.

Scutum the shield, Image credit: Nick Parke/Stellarium

Scutum is Latin for “shield” and was first introduced by the Polish astronomer Johannes Hevelius in Acta Euriditorium (a leading scientific journal of the day) in 1684. As the fifth smallest in the sky, Scutum Sobiescianum (to give the constellation its full name), was identified by Hevelius in gratitude to King John III Sobieski of Poland. ‘Sobieski’s shield’, which Scutum represents, honours the astronomer’s royal friend and ally who assisted with the reconstruction of Hevelius’ observatory after a devastating fire in 1679. So moral of the story? Never miss an opportunity to do an astronomer a good turn – you won’t regret it!  

Sagittarius the centaur, Image credit: Nick Parke/Stellarium

 

Moving down from Scutum to the horizon we land on the back of a mythical creature – the centaur Sagittarius! A well-known sign of the zodiac, this half-man, half-horse archer appears to want as many eyes as possible on him while he parades himself to stargazers both in the southern and northern hemisphere at the same time!  Since those of us in the northern hemisphere can only really see the top half of this somewhat untidy pattern of stars however, let’s look at it another way. A commonly recognised shape that can be found within these stars is a teapot! Literally resting on the table-top of the horizon the teapot is pouring to the right, with a handle on the left. However the nocturnal fun doesn’t end with a nice cup of tea, what about some chocolate? Or the ‘real’ Milky Way to be precise! With the summer providing observers in the northern hemisphere with an excellent opportunity to witness this huge city of stars in which we live in the outer parts.  The Milky Way Galaxy measures approximately 100 000 light years across (1 light year being about 6 trillion miles) and is populated by an estimated several hundred billion stars, of which our Sun is a fairly typical member.  We are offered a very special treat. For convenience right beside our teapot is the big bulge which forms the centre of our galaxy and where reside the highest concentration of stars and a supermassive black hole no less! So to know where to look, imagine steam blossoming out from the tip of the teapot’s spout and you are more or less there.

 

Galactic centre, Image credit: Nick Parke/Stellarium

 

If you own or can borrow a small telescope or even a good pair of binoculars, dust them down and run your eyes up the faint ‘milky river’ that rises from the horizon and runs overhead. Depending on how free from light pollution your viewing spot is and the quality of your optical aid you may be able to spot nebulae, globular clusters or even open clusters in this fertile patch of the sky! Nebulae are ‘clouds’ of gas and dust in space where stars are born or have exploded on their death. Open clusters are smaller and generally looser congregations of stars than globular clusters, also held together by gravity. Globular clusters however are a dying breed, as they are generally full of old stars and no young ones. One of the most spectacular globular clusters is Messier 15 or M15 which lies 35 000 light years away in the constellation of Pegasus. It measures about 120 light across, and gets more densely populated at its centre where it can be clearly seen with just a pair of binoculars!

 

Messier 15, Image credit: ESA, Hubble, NASA

 

Let’s move back up a little higher again to find another small constellation, often overlooked. To find it we are going we will be aided by a mythical creature and our bright ‘stellar beacon’ in the south – Altair. The mythical creature that will assist us is the Pegasus, a winged horse that in Greek mythology carried the hero Perseus on its back to rescue Princess Andromeda from the jaws of the great sea monster, Cetus. So to find Pegasus swing your eyes East of Altair until you find a large well-formed square of stars. This is the big chest and belly of the magnificent winged creature.

 

Pegasus and Delphinus, Image credit: Nick Parke/Stellarium

 

From here we are going to visit an aquatic animal constellation. So if you run your eyes from the top of the square back over to Altair, approximately two thirds of the way across you should be able to find a small diamond shape of 4 stars. Beneath the diamond and diagonally to the right is the 5th star of our constellation. In your mind’s eye therefore if you connect the stars with lines you would see the celestial pattern of a small kite. This is the constellation of Delphinus. Delphinus is Latin for dolphin and was one of the original 48 constellations catalogued by Ptolemy, the 2nd Century astronomer. Rotanev is the brightest star in this pattern with a magnitude of 3.6. The nearest star to us in the constellation is, in space terms, a relatively close 29 light years away. There are a few legends associated with the dolphin, one of which was that Delphinus was an emissary for Poseidon, the god of the sea. Poseidon admired and wished to marry the nymph Amphitrite who was one of the Nereids. Preferring, however, to stay in the company of her sisters, Amphitrite remained elusive. From the sea god’s point of view however, it was Delphinus that saved the day; although a number of messengers had been sent by Poseidon to Amphitrite, it wasn’t until the nymph heard the soothing tones and words of the dolphin that she was persuaded to return with Delphinus and become Poseidon’s bride.  

 

The dolphin, Image credit: Nick Parke/Stellarium

 

Another phenomena to keep your nocturnal eyes peeled for are Polar Mesospheric Clouds or Noctilucent clouds. These are clouds that can appear to glow across a large portion of sky after sunset, even when there is no Moon in the skyscape. So little was known about them that in 2007 NASA launched a special satellite to study them called AIM (Aeronomy of Ice in the Mesosphere). Since then a lot has been discovered. We now know that these special clouds are found unusually high, between 50 and 86km above the Earth, compared to the normal clouds which are found within the first 10km of the atmosphere. Noctilucent clouds generally have a high density of ice particles which reflect sunlight when the Sun is between 6-16 degrees below the horizon. Thanks to the higher position of these clouds above the Earth, they are able to catch and reflect sun rays after the Sun has dropped below the horizon.  This causes a silvery-blue post-sunset light show for any lucky observers who are in the right place at the right time to see it. 

 

Polar mesospheric clouds, Image credit: STS117-E-6998/NASA

 

Last, but not least, for those stargazers among us who live in a nice flat area or for those of us keen enough to take an evening trip up a mountain or hill to see above the usual skyline obstacles.  Saturn, the second largest planet of the Solar System may still be visible to you this month in the south as it marches its way progressively closer to the horizon. As the Earth turns on its axis, Saturn moves lower in the sky over the course of the evening, so the best opportunity to see it will be between 10:30pm and midnight, just after it gets dark.  So don’t forget to keep your telescope or binoculars handy!

 

 

Article written by: Nick Parke, Education Support Officer

Nick Parke, Education Support Officer