Last week I became the proud owner of an International DarkiSky Association T-shirt, complete with cool ying-yang motif and slogan - as they so eloquently put it, 'Every day needs a night'. How true, yet so often we don't realise what we are missing.
For example, when I was a child, the sodium street lights that lined the bypass of my home town lit up the night sky for many miles around with a sickly orange glow, completely wiping out all but the brightest stars. I don't remember noticing the Milky Way at all until I moved to Turkey. But now every time I go camping or sleep out on the roof in the summer, I am blown away by the glorious white arch across the night sky of our home galaxy.
Viewing our home galaxy, the Milky Way
Astronauts get an even better view, as you can see in this image taken from the International Space Station. The Milky Way is a disc-shaped spiral galaxy around 100,000 light years in diameter, and we are located towards the edge in one of the arms. That misty band of stars is actually the side-on view into its central disc. Looking away from the white band the stars are much sparser, as we are then looking outwards, through a much less dense part of the galaxy. All individual stars that we can see in every direction are actually part of own galaxy.
You have to look pretty hard to see anything outside the Milky Way. But it's possible! In good dark conditions, one of the furthest objects visible with the naked eye is our huge neighbour, the Andromeda Galaxy, also known as M31. It's over 2 million light years away, and with the naked eye it's a just small, fuzzy oval blur but clearly not a star. With a telescope it is spectacular – this view in ultraviolet light is from NASA's space-based GALEX telescope. It's a spiral galaxy like our own, but 2.5 times greater in diameter. Based on observations of its position in the sky, astronomers calculate that the two galaxies are moving together, and will eventually collide. But not for another 5 billion years, so there's no need to panic.
A universe teeming with galaxies Any further than this, and distant objects become incredibly faint. To maximise the chance of observing them, space agencies have placed a number of telescopes in space, to avoid the negative effects of light pollution, and atmospheric distortion – the best known is Hubble, which observes in visible light, but other successful ones include Chandra (X-rays) Spitzer (infrared). The results are often incredible – the multitude of jewel-like points in this image are all galaxies, some at unbelievable distances, up to 12 billion light years away. That means that their light has taken 12 billion years to reach us, and so we are actually seeing these galaxies as they existed when the universe was much much younger. We are actually looking back in time! Maybe we earth-bound observers have no chance of seeing such distant exotica with our own eyes, but find a dark-sky site and just look up - the night sky is full of wonders closer (relatively!) to home. |
http://www.darksky.org/
http://www.youcanseethemilkyway.com/#home
http://www.space.com/26901-milky-way-summer-observing-tips.html
http://www.space.com/15590-andromeda-galaxy-m31.html
http://astronomynow.com/2015/01/13/hubbles-high-definition-panoramic-view-of-the-andromeda-galaxy/
http://www.spitzer.caltech.edu/mission/235-Distant-Galaxies-and-Origins-of-the-Universe
1. NASA/Reid Wiseman http://www.nasa.gov/sites/default/files/thumbnails/image/iss041e045469.jpg
2. NASA/JPL-Caltech http://www.nasa.gov/mission_pages/galex/pia15416.html#.VVz1p0YqQvQ
3. NASA/JPL-Caltech http://www.nasa.gov/jpl/spitzer/pia18472