The Hydrogen Sky

Space isn't really empty. Sure, it's a better vacuum than any we've ever created on Earth, but it's still not quite empty. Most of the material in the interstellar medium is hydrogen gas, which we can map using radio telescopes. And make no mistake - thin it may be, but the structures in it are even more spectacular than what we see in normal visible light. It fills a much larger volume than the stars do, so even though it's very thin its total mass is comparable to that of the stars. Most people regard hydrogen as a galaxies "fuel tank" from which new stars ultimately form.

These images show what the sky would look like from various locations - using real data - if we could see the hydrogen directly with our eyes. You can learn more about how these images were created, and what the hydrogen tells us about our own and other galaxies, on my blog, which also has larger versions of the images.

One particlar feature - if we select just the right frequencies to study - really stands out. The Magellanic Stream is known to be around 200 degrees in lenght, more than half the sky ! It's thought to be gas removed from two nearby galaxies, the Magellanic Clouds. Only about 40 degrees would be visible from high northern latitudes, like Cardiff and Prague...

... but its full splendour would be revealed in the southern hemisphere :

And of course, you can also view this in animated form :