This is a little different to my usual posts. As it is visible on every post on this blog, I wanted to add a little explanation to the picture I chose to use as a banner

Full version of the Hubble image I chose for my banner. Click to go to a bigger version on Astronomy Picture of the Day. Credit: NASA/ESA/Hubble

The image up at the top of the page next to the "Basic Space" was taken by the Hubble Space Telescope and released in February this year. It shows a stellar nursery, known as NGC 2174,1 which is located 6,400 light years away from Earth in the constellation Orion.

Orion is full of nebulae, and NGC 2174 is one of the less well known ones. On the sky, it covers an area larger than the full moon, but is very faint. Because of this, it wasn't discovered until 1877, when French astronomer Édouard Jean-Marie Stephan spotted it using an 80cm reflecting telescope at the Observatoire de Marseille.

The Hubble image shows several young, bright stars (the ones that look pink) in and around the dark stellar nursery. These stars bombard everything around them with intense radiation, making the dust and gas in the nebula glow. NGC 2174 is mostly made up of hydrogen gas, which gets ionised by this radiation. Astronomers call regions like this H II regions because they contain lots of ionised atomic hydrogen (the H stands for hydrogen, the II differentiates from neutral hydrogen which is H I). The young stars in the image are making the gas in the nebulae not only glow, but disperse. Eventually, the mountains of gas and dust you can see will be completely gone.

The image was created by combining four pictures with different filters, all taken by the Wide Field and Planetary Camera 2 on Hubble. In the finished picture, ionised oxygen looks blue, ionised hydrogen is green, and ionised sulphur is red, as is the view through a near-infrared filter. If you are interested in seeing how Hubble pictures are made, there's a good video here showing the whole process. You can find some more information about how colours are used in Hubble images here.

When I was choosing my banner image, I had just been to see Hubble 3D at the Science Museum in London (I would definitely recommend it if you're in the area and have a spare couple of hours), which contains an amazing scene of the Orion Nebula and the young stars forming in it, so I had nebulae on the brain. NGC 2174 isn't part of the more famous Orion Nebula, but it's still pretty amazing in its own right.

  1. NGC stands for "New General Catalogue", and is a catalogue of deep sky astronomical objects that was complied in the 1880s. It contains 7,840 entries, including star clusters, nebulae and galaxies, but not individual stars or objects in the solar system.