I thought I’d take some time over the next few posts to give you some sources and links I’ve found especially useful as introductions to the science of the night sky. When people call to place an order, I’m often asked, with some incredulity, how on earth (love that expression) we can figure out what the sky looked like way back in [insert date here]. Speculation often goes to "do you have a vast archives of photographs? (admittedly, our prints do look photo-realistic, so I suppose this is understandable on some level), or (the most interesting take, in my opinion) to “using Hubble to ‘look back in time.’” Interesting concepts both, but no.

Observational Astronomy is rooted in Celestial Mechanics – the branch of astronomy that explores the slow dance of our moon and planets wandering in procession against the vast canopy of night – those million, million fixed points of light, the stars in our night sky. ‘Planet’ actually comes to us from the Greek, planetai, literally wandering.

The science behind what we do here has been worked out for hundreds of years, though until recently it’s been the exclusive domain of the mathematician/astronomer. Formulas for calculating the orbits of planets go all the way back to Galileo and Kepler in the 1600s.

Let’s start here with that list of resources. Stellarium is free, open source planetarium software for the PC, MAC and LINUX operating system. Seriously cool.

Stellarium is like the software that we use here at Indigo Night. I can’t believe it’s free… it’s really a remarkable piece of work. This will put a virtual planetarium on your desktop. The controls are very simple and intuitive. Elegant. Pick a location, key in a date and time, and there’s the sky. It will give you a horizon line with illustration and compass point to orient yourself, unlike many internet astronomy references that bear no relation to what you see when you look to the sky… at least at first glance. Click and drag to rotate your view.

You can go back and look at the sky on the day you were born, or when your child was born. The night you fell in love. The night you married. And, of course, it’s predictive. That’s how most star-gazers use a program like this: to plan an observation session. What will be visible in the sky tonight? Will Saturn stand above the treetops at nightfall? For the naked eye observer new to the night sky, on the other hand, it tends to be used more as a real-time chart, or legend, of the sky. It answers the question “What’s that bright object low in the southeast at nightfall?” A UFO? Or perhaps Venus?

Play with the date. You’ll see that each year, on a given date at a given hour, the stars are, for all intents and purposes, in the same place. If you look out the window of your grandfather’s upstairs bedroom on say, November 4 of 2009 at 11 PM, you’ll see very nearly the same star filled sky that your grandfather saw at 11 PM on November 4th of 1939.

Now, the moon and planets will be different –– that’s the part I find so interesting. The great clockwork of our night sky. Each planet orbits the sun in it’s own sweet time – earth in one year, obviously. Saturn takes about 30 years. Jupiter about 12, moving through roughly one sign of the zodiac each year. Venus takes about 7 months, moving from ‘Morning Star’ to ‘Evening Star’ and back, as its orbit takes it behind (or in front of) the sun, lost from view to us for several months, then back out into the night sky.

These infinite variations in the pattern of the night sky, this regal dance in the heavens, slow, majestic, and absolutely, steadfastly, correct… that’s the beauty of it, to me, connecting all of us, across cultures and time. We all share a common frame of reference, our small blue-green planet, this island earth. Enjoy the view.