When we look up at the night sky to see the stars, we are amazed at the vast brilliance above us. Especially when you realize that you are on a small rocky, blue planet swirling across this massive, unimaginable ocean of stars. Though there are billions of stars in the sky, there are very few that we can easily see and identify with our unaided eyes. Ancient observers have connected these stars into constellations, a group of stars that appear to form a pattern or picture like Orion the Great Hunter, Leo the Lion, or Taurus the Bull. Constellations help us orient ourselves using the night sky with easily recognizable patterns. As the astronomers study the night sky with the most modern telescopes, they are able to see more stars and understand them better. In all we have around 88 constellation regions.
British astronomer Edmond Halley, who also has a famous comet named after him, was one of the first to observe that stars move. Today we also know that stars age and that the light we see today might have left the star thousands of years ago. So technically, we when we see stars today, we are looking-back! Because of the finite speed of light, when you gaze up into the night sky, you are actually looking into the past.
The Andromeda Galaxy is the most distant object readily visible to the naked eye and it is 2.5 million light years away. The light from it that we see right now is 2.5 million years old. We are therefore seeing the Andromeda Galaxy as it was at a time long before modern humans existed!
The bright star Sirius is 8.6 light years away. That means the light hitting your eye tonight has been traveling for 8.6 years. To explain it in a simpler way, you are seeing Sirius tonight as it was 8.6 years ago.
Are all the stars in the constellations fixed and don’t change? Not at all, as each of the stars vary greatly in size, distance from Earth, and temperature. Sometimes, some of the dimmer stars may be smaller, farther away, or cooler than brighter stars. However, the brightest stars are not necessarily the closest. Of the stars in Cygnus, the swan, the faintest star is the closest and the brightest star is the farthest! So each of the stars in the constellation varies in distance and time and is not necessarily in the same place!
So the next time you look up at the sky, remember you might be looking back in time or a collection of times!