Constellation of the Month – August: Lyra

August marks the return of proper darkness down south, or as proper as darkness gets in Lahndahn Town. This is the time when the serious astronomer dusts down their telescope and prepares to sally forth once more…

 
So, in a new feature on this blog, I'm going to present a monthly guide to one constellation. And to kick us off I choose… Lyra, the Lyre.

 

The Summer Triangle

Lyra

Lyres are maybe not familiar instruments to us these days. Basically, they're like little harps, and it doesn't actually take much imagination to see a Lyre in this pattern in the sky. This is quite rare for astronomy, where four really faint stars can make up the constellation of the Giraffe. To find Lyra you'll need to look high in the sky for a large triangle of stars colloquially known as the "Summer Triangle." The highest one is Deneb, the lowest is Altair and the middle one is Vega, and this last one is the brightest star in Lyra. In fact it happens to be the fifth brightest star in the sky. Next to Vega you'll be able to make out a parallelogram (Going back to those school maths classes) of four other stars, and this makes up the bulk of the constellation.

Image credit: free software Stellarium, http://stellarium.org

It was one of the original 48 star-patterns named by Ptolemy the Greek-Egyptian astronomer around the 2^nd Century. You might be wondering whose Lyre it is – it belonged to the mythical Greek musician Orpheus whose musical abilities were such that he could charm all living things and even stones. Quite why he wanted to charm rocks is unknown – go with it, this is Greek myth. He was eventually killed and his Lyre was thrown in the river – Zeus ordered an eagle to find it and then put both Lyre and Eagle into the heavens where they because the constellations of Lyra and Aquila. Why an eagle? That's not an aquatic bird – an osprey would have been a far superior choice. Or a gannet.

 
Joking aside, Lyra packs quite a punch for such a titchy constellation. Here's a guided tour of the highlights:

• Vega – Alpha Lyrae is kind of a gold standard for stars because it's at magnitude 0 (Well 0.04 to be precise). The brightness of all other stars is measured relative to the brightness of Vega, which is something of a claim to fame. Look at it through a telescope and you'll see it's pretty bright and a cold bluey-white colour. Most of its interesting facets are invisible to the eye, even with a telescope – it lies at 25 light years so is pretty close by, and it's twice the mass of the sun. This means that its lifespan will be a tenth of our own star's. Most bizarrely, its rotation is so rapid that it bulges outwards at the equator, something that can only be inferred rather than viewed directly. 
• Epsilon Lyrae – The Double-Double – A lot of stars are not solitary like our sun, but are double star systems, mutually bound together by gravity. Epsilon Lyrae outdoes these though because it's a quadruple star. With the naked eye it appears as a single star above and to the east of Vega. Through binoculars you get a different story as it resolves into two separate stars staring down at you like cat's eyes. But with a telescope and a bit of magnification you'll see that each star is actually two stars, very close together. It can be resolved easily, even from London, and is a bit of a classic test of the seeing conditions. 
• M56 – An example of a globular cluster, a dense conglomeration of ancient stars formed at a very early stage in the history of the universe. They hover round our galaxy like a halo of flies, and M56 is one of the brighter ones, although still a challenging object here in London. There's not terribly much more to say about it – you really want a telescope to find it and with even my 6'' Dob all I get is a fuzzy disc of light. 

  

  The Ring Nebula - Image Credit: NASA

• M57 - The Ring Nebula – Saving the best until last, we finish with the classic example of a planetary nebula. Once again science seeks to confuse us because it has nothing to do with planets. Planetary nebulae present discs when viewed through a telescope so look like tenuous planets. The Ring is a bit special though and one of my top objects for viewing under light polluted skies. Although it's relatively faint at magnitude 9, it's small so its light is concentrated in one place – high surface brightness. It lies between the bottom two stars of the parallelogram, pretty much midway, but you need a telescope to see its secrets. With low power it looks like a faint fuzzy star, but crank up the magnification and strange things happen… With averted vision (I.e. not looking directly at it) you'll see not a disc, but a tiny ring of light. Using a nebula filter will enhance this effect, and even my little 3'' refractor shows it. The Ring Nebula is the remains of a star – when stars of around the mass of our sun run out of fuel they first expand to use up their supply of helium before shrugging off their outer layers leaving a puffy planetary nebula and a faint white dwarf star; all that remains of the core of the star. It's slightly macabre to think that one day our sun might look like this – makes you want to enjoy life and look after our planet because it's the only one we've got…