I’ve been on a space and astronomy kick since the 40th anniversary of the Apollo moon landing was celebrated last month. I just finished reading This New Ocean: The Story of the First Space Age, by William E. Burrows. It’s incredibly thorough, covering all aspects of the space program from humanity’s first strivings to fly into space, through Galileo’s discoveries, through the development of rocketry, all the way to the end of the 20th century. (The book was published in 1998.) Now I’ve moved on to The Fabric of the Heavens, a history of astronomy from Babylonian times to the discoveries of Newton.

I’ve also discovered an amazing free downloadable computer program, Celestia, that lets you simulate travel throughout the universe. It contains models of every planet and moon in our solar system, rotating and revolving at their actual speeds, as well as pretty much every star we know about; man-made satellites, such as the International Space Station and the Hubble Telescope, in their proper places; comets; and countless galaxies. You can see things from any vantage point, you can speed way up or slow way down, you can move around. It’s also expandable — you can download addons for numerous spacecraft, comets, asteroids, and even fictional planets and spaceships, such as the Enterprise or the Death Star, Vulcan or Tatooine.

You can do so many cool things with it, and playing around with it can bring interesting insights. For instance, if you zoom way out so that so you can see the sun and the first four planets, and then tell the program to put Earth at the center of your screen and keep it there no matter what happens, and then speed things up, it looks like the sun and the planets are orbiting around Earth, just like the ancients thought. Venus and Mercury do these weird loop-de-loops around the sun, creating the epicycles that we see here on Earth, while Mars looks like the “wandering star” people used to think it was.

Or you can go to the surface of Mars and see the Earth as a tiny dot, just as Mars looks like a tiny dot from Earth. Or you can go to another star and see the Sun itself as just another dot.

Or you can press a button that shows you the lines that make up the constellations, and then you can zoom way, way out from the Sun, past Neptune, past Pluto, without the constellations seeming to change shape at all. They don’t start to change shape until you get about 0.1 light years from the Sun. That’s how far away they are! We know this intellectually, but it’s amazing to see it actually simulated.

I don’t know why I never knew about Celestia, but it’s my new toy, and it’s absolutely free.