26 May 2016 by Brian Jones
For summer, we are turning our attention to the small but relatively conspicuous constellation Scutum (the shield) which, during the months of northern summer, is located a little way above the southern horizon as seen from mid-northern latitudes. The chart below depicts the main stars visible in the night sky during the months of northern summer/southern winter. It shows Scutum along with the three prominent stars Vega (in Lyra), Deneb (in Cygnus) and Altair (in Aquila) which together form the Summer Triangle, a conspicuous configuration of stars that is at its most prominent around this time of year.
As far as stargazers located at mid-northern latitudes are concerned, Scutum is best sought out during the months of July and August when it will be at its highest position above the southern horizon. Given a clear and moonless night, you should be able to spot the stars that form this little group with the naked eye. If you have any problems with moonlight or light pollution, a pair of binoculars will help you to track it down. Located immediately to the southwest of Aquila, as shown here, the whole of Scutum is visible from mid-northern latitudes, and portions of the constellation can be seen worldwide, apart from some regions in the Arctic, which should not pose too many problems for the average rambler and backyard astronomer!
In order to track down the quadrilateral of stars forming Scutum, you first need to locate the bright star Altair in Aquila, the southernmost star in the Summer Triangle. Then follow a line south westwards from Altair, through the nearby trio of stars – Deneb Okab, Lambda and 12 (all in Aquila) – and on a little further to Scutum itself.
Scutum was introduced in 1684 by the Polish astronomer Johannes Hevelius in honour of King John III Sobieski of Poland. The original name given by Hevelius to the constellation was Scutum Sobiescianum (Sobieski’s Shield). This was in recognition of the fact that King John III Sobieski was a distinguished warrior, although the name of the constellation has since been shortened to Scutum.
A closer look at Sobieski’s Shield
Although the overall shape of Scutum is distinctive, none of the stars that form it are particularly prominent, the brightest being Alpha, a magnitude 3.85 orange giant shining from a distance of around 200 light years. The northern tip of the constellation is depicted by the magnitude 4.22 yellow supergiant star Beta, the light from which has taken 900 years to reach us, having set off on its journey towards us around the time King Henry I was on the English throne!
Magnitude 4.88 Epsilon is a yellow giant shining from a distance of about 530 light years, somewhat more distant than Delta, a magnitude 4.70 star situated around 200 light years away. Located at the southwestern corner of Scutum is Gamma, a white star with a magnitude of 4.67 located at a distance of about 300 light years. (Click to read more on star names and colours.)
Scutum lies in a rich and star-packed region of sky, playing host to a large, bright section of the Milky Way, and is a wonderful target for the backyard astronomer using either the naked eye or binoculars. This area is known as the Scutum Star Cloud and is one of the richest sections of the Milky Way. Here, no interstellar dust blocks out the light from the star fields beyond and, when viewed under clear dark skies and from areas unspoiled by light pollution, this portion of the Milky Way really stands out well.
The American astronomer Edward Emerson Barnard described this region of sky as being a ‘gem of the Milky Way’. This echoes the comment made by the American astronomy writer William Tyler Olcott who, in his book Star Lore: Myths, Legends, and Facts, tells us ‘it is said that within the boundaries of Scutum, in a space five degrees square, [the astronomer] Sir Wm. Herschel estimated that there were 331,000 stars.’ These comments certainly highlight the richness of the Milky Way in the tiny constellation of Scutum. Check out the Scutum Star Cloud for yourself and see if you agree with Barnard and Herschel!
Watch out for wild ducks
The open star cluster M11, also known as the Wild Duck Cluster, is situated at the northern edge of the Scutum Star Cloud. Shining from a distance of around 6,000 light years, this prominent object contains almost 3,000 stars and glows with an overall magnitude of 6.3. M11 is a reasonably easy target for binoculars, which will reveal it as a faint misty patch of shimmering light, although you will need a small telescope in order to resolve any individual members of the cluster.
Discovered in 1681 by the German astronomer Gottfried Kirch, who described it as ‘a small obscure spot’, the cluster derives its popular name from comments made about it by the English astronomer William Henry Smyth. He likened its appearance to ‘a flight of wild ducks…a gathering of minute stars’. M11 forms a small triangle with the nearby stars Beta and Eta and, given clear dark skies and a bit of careful searching, you should have little trouble tracking this object down.
So take a trek out to a dark sky site, or simply venture into your own backyard, and check out the tiny but nonetheless interesting quadrilateral of stars that depicts Scutum, the celestial and star-studded shield of King John III Sobieski of Poland. Happy stargazing!
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