Alien Astronomers

Looking out at the stars tonight, it was so clear that I felt I had to make use of my astro setup.

I was just cruising along the Milky Way, star after star after star. There are three hundred billion of them. Three hundred billion stars make up the Milky Way. I had to look that number up, because every time I see the number somewhere, the estimate has risen again. While looking at some of our neighbours I heard some statistics on a podcast that set me thinking of the Drake Equation. As loathe as I am to say never, I'll risk it this time to say it is one equation that will never be solved.

Professor Drake probably got asked the question a lot more than I am, and almost everyone asks me, 'Are we alone?' So he worked out a formula for estimating the number of planets with intelligent life. It is very long and I won't go through each term tonight but given the last estimate I read on the number of stars in our galaxy was two hundred million, multiplying guesses over guesses and you get a lot of wiggle room in the final figure.

The Kepler satellite has discovered over three thousand planets in our galaxy, with more confirmations all the time. It is no longer news to find yet another. However we can get some surprising figures from the Extra Solar Planets they have discovered. It seems from the figures that there is around one planet for every star in our galaxy. That isn't to say there are planets around every star, there aren't, but as lots of stars have multiple planetary systems, it averages out to one each. One sixth of these are earth sized, that makes fifty billion earthlike planets just in our galaxy. Taking all of the other elements into account, the current guess is a figure upwards of 35 million intelligently inhabited and able to communicate their presence, planets in 'our' Milky Way.

On this planet we have around half a million amateur astronomers, and as only half that number is in darkness at any one time, we should divide by two. Out of those lets say 10% are actually using their scopes at any one time. So from earth we have twenty five thousand people looking through a scope at the sky, every night. If the thirty five million inhabited planets have astronomers in the same way as we do, that means as I was looking up tonight, there were 875 Million astronomers looking back.

So next time you are out at night, look up and smile, say 'Hi' to the neighbours. Some of them must be saying the same thing!