Adrian Dening's Stars Over Somerset

Wednesday, 5 June 2024 17:00

Monday 10th to Sunday 16th June 2024

Over the last few weeks I have been mentioning deep sky objects: open and globular clusters of stars, areas of gas known as nebulas and galaxies which are collections of billions of stars, like our own Milky Way.

Well there are actually five different types of nebulas and I am often asked about them, so thought it would be an interesting topic for Stars Over Somerset.

First of all we have "Emission Nebulas" and the best example is the Great Orion Nebula, M42 in the Charles Messier catalogue. These are large areas of ionised Hydrogen gas that emit light and they are "stellar nurseries" where stars are being born.

Secondly we have "Reflection Nebulas" such as M45. Hang on.....isn't M45 the Pleiades open cluster of stars? Well yes it is, but with a powerful telescope, you can see the remains of the gas that created the stars - the gas isn't giving off its own light anymore, but it is illuminated by the reflection of light coming from the recently-formed stars.

The next type of nebula is known as a "supernova remnant" such as the Crab Nebula M1 in the constellation of Taurus. These nebulas are the leftovers from a star that has exploded as a supernova.

Then we have "Planetary Nebulas" that have nothing at all to do with planets! A good example is the Dumbbell Nebula M27 in the Summer Triangle. These are glowing ionised gases ejected from a dying red giant star. The misnomer originates from the 1700s when using early telescopes, astronomers thought their round shapes looked like planets!

Finally, a "dark nebula" like the famous Horsehead Nebula in Orion is a cloud of gas and dust that is revealed due to the bright material and stars behind it. The nebula is silhouetted against the bright background which creates interesting shapes.