The Andromeda Galaxy is an unfathomably large collection of stars. It is estimated that some one trillion stars lie within it (that's a one followed by 12 zeros). Each of these stars are entire suns in their own right, with many of them likely harbouring planets around them. The Andromeda Galaxy is accordingly the largest galaxy in the local group, which is the cluster of galaxies containing our home galaxy, the Milky Way. Light, the fastest thing known in the Universe, travels at an astonishing 300,000 kilometres a second. Even airplanes, the fastest mode of transport available to most of us, would take nearly 50 hours to traverse across the globe. If we could travel at the speed of light, we could repeat this 50-hour journey 7 times in a single second. 

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Even travelling at this speed, however, the light collected by my camera sensor spent nearly 2.5 million years traversing across the void of intergalactic space. The photons of light that ended its journey inside this camera were emitted by stars in the Andromeda galaxy long before the first human even walked on Earth. Images of distant galaxies, in essence, allows us to look straight into the past. The photograph you see of the Andromeda Galaxy therefore only shows how the galaxy looked like more than 2 million years ago.