Planetary Nebulae

Planetary Nebulae are designated as such because they look like the disks of planets at first glance. This holds true in particular for their discovery in the 18th centrury when the quality of telescope optics was not comparable to nowadays' technique. Towards the end of their lifetime, stars with a mass comparable to that of our sun go through an astronomically short phase (a few 10.000 years), in which they rid a lot of mass, owing to instabilities. The left-behind is a rather compact and hot White Dwarf. The ejected gas envelope forms a nebula. The emerging surface of the star is extremely hot - up to 30000 K - and emits intensive UV radiation, which heats the ejected gas to about 10000 K, thereby ionizing it.

Dumbbell Nebula M 27 (NGC 6853)

Maksutov-Newton, Canon 1100Da, 5.9 hours

Another example is the Dunbbell Nebula, 1400 ly away. Its diameter is about 3 ly, somewhat less than the distance from us to the next star. The central star blows off its gas envelope 'in agony': the blue-coloured gas in the inner part is oxygen, while the purple one is hydrogen.

Helix Nebula NGC 7239
Maksutov-Newton, Canon 1100Da, 10.2 hours

A nice planetary nebula is the Helix Nebula. One can just see it with a good binocular. As it is only 650 ly away from us its angular size is much larger than for instance that of M 57. The Helix Nebula is located at a low (-21°) declination. It was only after cropping a couple of trees close to my observatory that I could reach this marvellous object...

Ring Nebula M 57 (NGC 6720)

Maksutov-Newton, Canon 1100Da, 33 minutes

With 2300 ly the Ring Nebula is a lot more distant and hence appears at a much smaller angular size. Its structure and colours are similar to those of the Helix Nebula. High up in the summer sky, this is a worthwhie target for all amateur astronomers, and a little challenge for beginners.