Know your constellations: Lyra the Lyre

Know your constellations: Lyra the Lyre

Published by Nick Lomb on September 7, 2011 3 Comments

Lyra

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!

Ring Nebula in Lyra with New Mexico telescope 29 Sept 2004

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.

Leave a Reply

3 Responses to “Know your constellations: Lyra the Lyre”

  1. September 09, 2011 at 4:27 am, Andrew James said:

    As a writer specifically on planetary nebula (I.e. The “Neat Southern Planetaries Series” that once appeared in the Astronomical Society of N.S>W. “Universe”, and on-line at the “Planetary Nebulae Observer’s Home Page” @59deccc973e8cced4309a71e5f9f05cf:disqus It http://www.blackskies.org/nsp01.htm )

    The Ring Nebula (M57 / NGC 6853 / He2-452 / PN G 60.8-3.6) is fairly bright, being listed as 8.8v or 7.6p magnitude for its 230 arcsec sized ring. Even 7.5cm. (3-inch) telescope will clearly show the smokey annular ring. At a distance of 700±325 pc. or 2300±1100 ly., the projected diameter is 0.7±0.3 pc (or 2.6 ly) across.
    The Ring is expanding at about the rate of nebula expansion is roughly 1 arcsec per century, making the minimum age about 3300 years. Earlier estimates find ages a low as 1,610±240 years.
    The Ring nebula is also known as an example of the so-called bipolar planetary nebula (BPNe). Simply, the central oval ring is caused by the projected waist aligned about 30 degrees to the line of sight. 

    As for the central star;

    The central planetary nebula nucleus or PNN was discovered by Hungarian astronomer Jenő Gothard on September 1, 1886 from images taken from his observatory in Herény, near Szombathely. This 0.615±0.05 Solar mass PNN white dwarf consists primarily of carbon and oxygen, and has avery  thin outer envelope of lighter elements, with the surface temperature of 125000±5000 K and some 200 times more luminous than the Sun. Visual magnitude is only 15.8v.

    It is the emission of ultra-violet light from the white dwarf PNN that makes the nebulosity glow so brightly.

    When one thinks of planetary nebula, observers tend to think either of the Ring Nebula, the Dumbbell  Nebulae in Vulpecula or the Helix Nebula in Aquarius. Best in the southern skies are the Spiral Planetary / NGC 5189 in Musca or NGC 3195 in Chameleon and the bright, but small “the Blue Planetary” NGC 3918 in Centaurus. [NGC 3918 I have seen from Sydney Observatory too in the large 11.7-inch refractor.] 

    Reply

  2. September 08, 2011 at 3:03 pm, Andrew James said:

    Dr. Lomb. Interesting article that reminded me of my early experiences observing deep-sky at Sydney Observatory.

    At the age of twelve, one of my first views using the observatory’s 28cm Refractor was the two ‘car lights’ of Alpha Centauri. 
    On another night sometime in October in the early 1970s, I asked the night assistant, the late Assistant Government Astronomer Ken Sims, if I could try to find the Ring Nebula in Lyra. 
    I still recall his adamant and direct remarks that it was not possible to see it in city skies. However, he offered to me the opportunity to “control the big telescope”. Pushing the telescope was a little difficult for me at that age, and worst I could not see the object in the finder. 
    After a minute or so, I fixed the telescope mid-way between the two stars at the top of the Lyre. To my own amazement (and likely Ken Sims), I had found the faint misty smoke ring, finding my first true deep-sky object. 
    We also looked at Epsilon Lyrae – the famous double double – but the two closer doubles were not split, probably due to the seeing conditions.

    This observing was neat stuff, and I have been observing ever since!

    Reply

    • September 09, 2011 at 12:34 am, Anonymous said:

      Hello Andrew. Thanks for sharing those remembrances. You did well to find and to see a faint object such as the Ring Nebula from Sydney Observatory, although light pollution would have been less in the the early 70s than today. The only time I saw it through a telescope was from a dark country site and somebody else found it for me!

      Reply

Search

About

The 'Observations' blog is run by the staff of Sydney Observatory which is located at Observatory Hill, The Rocks, in Sydney, Australia.

This site is for discussion purposes only and does not represent the official views of Sydney Observatory. Any views expressed on this website are those of the individual post author only. Sydney Observatory accepts no liability for the content of this site.

Please direct any correspondence about the content of the blog to:
observatory [at] phm.gov.au
and about web matters to:
web [at] phm.gov.au.