Know your constellations: Lyra the Lyre
The northern hemisphere constellation of Lyra the Lyre with its bright star Vega. Drawing Nick Lomb using Stellarium software
Did you know there is an upside down lyre hanging low in the northern sky each evening after dusk? This is the best time of the year to see the famous northern constellation of Lyra the Lyre from the southern hemisphere as it is at its highest (though still low in the northern sky) in the early evening.
The story of the Lyre from the ancient Greeks is that Apollo gave it to his son Orpheus, the musician. Orpheus played the lyre to accompany his mournful songs as he attempted to release his wife Eurydice from the underworld after her early death. The music was so moving that he almost succeeded except that he turned back to look at her earlier than he was allowed to and she vanished for ever.
The only bright star in the constellation is Vega. This is the fifth brightest star in the sky and one that astronomers use as a standard star with which to compare other stars. In recent times this role for the star has turned out to be somewhat awkward for it has been discovered that instead of being a slowly spinning star as had been thought, it is a fast spinning star viewed with its pole facing us. This spin distorts the star so that it is much broader at its equator than at its poles: through its poles its width is 2¼ times that of the Sun while at its equator it is 2¾ times wider than the Sun.
Vega is 25 light years from us and is surrounded by a disc of dust that glows in infrared. Possibly the disc is a system of planets that is forming or that will form from the disc. Another distinction for Vega is that due to the wobbling of the Earth’s axis (precession) in 11 000 years or so it will become the northern hemisphere pole star, a role presently filled by Polaris.
Another famous object in Lyra is the Double Double star. In good conditions from the northern hemisphere where the star can be high in the sky, some people claim to actually make out the two components of the star with their unaided eyes. For us, with the star low in the northern sky, binoculars are necessary to do the same. Still, this possibly is the only double star that can be so easily seen.
Interestingly, each of the components of the Double Double star are themselves double. The close pairs circle each other roughly once a thousand years while the two visible in binoculars are believed to take about 500 000 years. Don’t expect any change as you watch!
A wide-angle view of the Ring Nebula in Lyra. Image taken at Sydney Observatory on 29 September 2004 using a telescope in New Mexico
The most famous object in the constellation is the Ring Nebula in Lyra. A telescope at a dark sky site is needed to see this planetary nebula or dying star. Planetary nebulae are stars that throw off their outer envelopes at the end of their lifetimes and leave behind a very hot remnant . This hot remnant excites the thrown off gas to shine in different colours that depend on the intensity of the radiation, which drops off with increasing distance from the central star.
The age of the nebula can be estimated from its rate of expansion and turns out to be somewhere between 6000 and 8000 years. Like the case with all planetary nebulae, the distance of the Ring Nebula is hard to estimate, but one suggestion is that it is about 2300 light years from us.