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Astronomy Picture of the Day


Esilon Lyrae - The Double Double: multile star system

M57 - The Ring Nebula: planetary nebula

Epsilon Lyrae - The Double Double Multiple Star System B L H

This is perhaps the best multiple star system that can be easily observed! Look first with binoculars and find Vega, at magnitude -0.04 the fifth brightest star in the heavens and one of the stars that make up the Summer Triangle. Centre the field of view on Vega and, to the east and a little north, the two "stars", epsilon1 and epsilon?, that make up Epsilon Lyrae will be seen as a double separated by 208 arc seconds. Once found you may, given keen eyesight, be able to "split" the double using just your eyes. Each of the two "stars" is just brighter than 5th magnitude.

If you observe them with a telescope using reasonably high power when Lyra is high in the sky and the atmosphere is steady, you should see that each of the two "stars" is itself a double, one orientated along the line joining the two major components, one at right-angles to it. The former pair (epsilon1) are of magnitude 4.7 and 6.2 separated by 2.6 arc seconds with the latter (epsilon2) having magnitudes of 5.1 and 5.5 and separated by 2.3 arc seconds a small separation, which is why the seeing has to be good to split them. They all appear white to the eye. Each pair is orbiting each other with periods of ~1200 (epsilon1) and ~600 (epsilon2) years whilst the two pairs are also gravitationally bound and orbit each other about once every million years.

Position: 18h 44.3m +39deg 40min

Epsilon Lyrae

M57 - The Ring Nebula Planetary Nebula M H

Perhaps the easiest planetary nebula to observe, the Ring Nebula looks like a smoke ring or doughnut. It lies just below the line joining Gamma and Beta Lyrae being slightly closer to Beta Lyrae. Just sweep a telescope between the two stars and, given reasonably dark skies, it should be immediately obvious. It has a magnitude of 8.8 and is 1.4 by 1.0 arc minutes in angular size. It is now believed that it is a shell or possibly a cylinder of bright glowing gas that was blown off when the progenitor star exploded leaving the very hot (~100,000K) white dwarf star that is seen at its centre in photographs. This bluish compact object, about the size of the Earth, is only 15th magnitude and so, whilst showing up well in photographs, will only be seen in the biggest backyard telescopes. Ultra-violet light emitted by the white dwarf excites the surrounding gas to glow. The most recent estimates give M57 an age of about 7000 years. It is thought to lie at a distance of just over 2000 light years and is about half a light year across - or 500 times the size of the solar system.

Position: 18h 53.6m +33deg 02min

Ring Nebula