This Month, Saturn and Arcturus Show Us How Big Space Really Is

Space is big. Really big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space. — Douglas Adams The Hitchhiker’s Guide to the Galaxy

It really is!

Tonight around 9pm, look up in the Eastern sky to see one of the brightest stars in the sky, Arcturus in the constellation Boötes. This orange-giant star is the fourth brightest in the night sky. If you follow it a bit to the south, you’ll see two other bright objects: the planet Saturn and the star Spica, respectively:

Arcturus and Saturn in the May sky

Big numbers

Arcturus is around 25-times bigger than our Sun (i.e., 25 times the diameter). And, it’s around 36.7 light years away. A light year is how far light travels in a year at a speed of around 186,000 miles per second (see my blog about measuring the speed of light). So, Arcturus’ light took about 36.7 years to reach our eyes. That means we’re seeing Arcturus as it was when Gerald Ford was President, by the way.

Now, since there are around 6 trillion miles in a light year, Arcturus works out to be approximately 220 trillion miles away. Saturn, on the other hand, is around 12-times smaller than the Sun (i.e., 1/12 the diameter), and, it’s around 720 million miles away. So, we’re seeing it as it was just an hour and five minutes ago.

Here’s the mind-blowing bit:

Given that Arcturus is ~220,000,000,000,000 miles away and Saturn is a “mere” 720,000,000 miles away, Arcturus is around 306,000 times further from us than is Saturn! Yet, on the scale of the Universe, it’s practically around the corner!

Now, the Cassini-Huygens probe to Saturn sped along at up to over 50,000 miles per hour. At that same speed, it would take half-a-million years to reach Arcturus.

So, when you look up and see both Arcturus and Saturn, just think about how different and how far apart these two apparently bright objects really are!

Space is big. Really big…