Go outside and look at your hand. You can say with a reasonable degree of accuracy that the light hitting your palm took 8 minutes to get there. How? Because we know the distance of the sun (~93 million miles) and how fast light travels (~670 million miles per hour). This means the light we see from the sun is actually light from 8 minutes ago. Light is a time machine that allows us to look back in time. This thinking applies to all things. Every person you see is that person slightly in the past. Venus, the brightest thing our night sky other than the moon, is sooo 4 minutes ago. The greater the distance, the further we can look back. Now consider this image:
This mind-blowing view is of the Orion Nebula, and it's the sharpest we've ever captured. It's situated 1,500 light-years away, so it took 1,500 years for the light to reach us from that distance. Let's put that into perspective - the image we're seeing is actually the Orion Nebula 1,500 years ago. Where were we? In a bit of a rut, commonly known as The Dark Ages.
Click the image to grab the high-resolution wallpaper, or learn more about it here.