The galaxy in the photograph, NGC 7331, is sometimes known as the Milky Way's twin. It's 40 million light years from where we spin in space, but it probably provides the best idea as to the Milky Way's colour - a whitish, yellow glow with a faint blue tinge.
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Some galaxies are very blue, usually when they are first born and dominated by large, fast-burning stars that die out relatively quickly; others are red, dominated by smaller slow-burning stars. Ours is in the middle.
''It is actually hard for us to work out the colour of our own galaxy, because we are in the middle of it,'' says Melbourne astronomer Michael Brown, lead author of an international research paper An Atlas of Galaxy Spectral Energy Distributions from the Ultraviolet to the Mid-Infrared, to be published next month. In short, it's a guide to the colours of 129 ''nearby'' galaxies.
Dr Brown, a Research Council future fellow at Monash University, says the atlas is designed to allow astronomers to precisely measure the colours of galaxies - a complicated task given the expansion of the universe stretches light, which in effect changes the colour of an image being beamed from its distant source. ''The classic analogy is to compare sound and light,'' Dr Brown says. ''When a car travels towards you the sound waves get squashed together and you hear a higher pitched engine sound. When a car travels away from you the sound waves get stretched and you hear a lower pitched engine sound.
''When a galaxy travels towards you, the light waves get squashed together and the light becomes bluer. When a galaxy travels away from you the light waves get stretched and the light becomes redder.''
The question then becomes: what was the colour of the galaxy at the time it emitted the light being observed?
''We need some way of determining how much light galaxies produce across the spectrum, including ultraviolet, visible and infrared light. This is a tricky problem, as it requires combining observations taken with a variety of satellites and ground-based telescopes,'' Dr Brown says.
The colour image of NGC 7331 mimics what we would see with our own eyes. ''When constructing the atlas, a total of 23 images of NGC 7331 from a variety of ground-based and space-based telescopes were used, including five Sloan Digital Sky Survey images.''
Further complicating matters is the diversity of galaxy shapes, sizes and colour. As they age, the universe is changing colour, from blue to red. Given current theory holds that the universe will keep expanding for ever, that's going to be one big blush.
