Nebulae
Look at the night sky and if you are very lucky you may spot the odd star that looks just a little bit fuzzy, don’t worry its not your eyes. Scattered throughout the Galaxy are patches of material we call nebula. Their name comes from latin and literally means cloud and that’s just what they are, interstellar clouds of predominantly hydrogen gas and dust.
If you are lucky enough to own a telescope or binoculars then try pointing them at a nebula such as the Great Orion Nebula in Orion and you will be reveal delicate filaments and wispy structure that gives them the fuzzy appearance. The Orion Nebula really is a fine example and has a distinctive red and blue look to it which is pretty typical of this type of object. If a nebula lies close to stars then the energy from them is enough to cause the gas atoms to energise and start to shine, we call this an emission nebula and they are usually red in colour. For those that are a little too far from the star to cause it to glow then we see the starlight reflected off the dust particles as a reflection nebula giving it the distinctive blue colour.
Over millions of years, gravity slowly takes control and causes the cloud to collapse and as the temperatures and pressures increase, crucial nuclear processes start. Hydrogen atoms start crashing together forming different elements and in the process release a tiny amount of heat and light and its this, that marks the birth of a star. Inside the Orion Nebula a number of stars have started to shine and you can see some of them through telescopes in the centre of the cloud. Eventually, over many millions of years, the remaining material in the nebula will slowly get blown away into the depths of space to eventually come together again to form more new stars.
Its not quite as simple as that of course as some of the material will remain in orbit around the new hot young stars and form planets which is how our Solar System formed around 5 billion years ago.
Not all nebula on view is as a result of stellar birth, some are the result of the death of stars such as the stunning planetary nebula which, through small telescopes look a little like planets. When our Sun dies in around 5 billion years time, its thought it too will loose its outer layers in its final death throws and form a planetary nebula. More explosive deaths lead to the star being blown to pieces in a fraction of a second leaving behind stunning supernova remnants.
For those clouds that haven’t yet collapsed enough to start the nuclear process of stellar birth nor are related to the end of a star’s life then they appear just as dark clouds lurking in space. The only way to visually see them is if they are sillhoueted against background stars or nebulae. We call them dark nebula and a good example is found close to the Orion Nebula called the Horsehead Nebula.
Mark’s Observing Tip
Through telescopes, nebulae can be stunning. Don’t expect to see them as you see them in pictures though. Camera’s are much better than our eyes at detecting colour when light levels are low so when you look at nebulae, you won’t see the colours that you see in the pictures.
