Imagine that you’re standing on Earth and there’s a satellite right over your head, parked perfectly still in the sky. For months, maybe even years, … Read More

It is a little geometry and a little energy. Two numbers, the farthest point (apoapsis) and the closest point (periapsis) (form the shape of an … Read More

The shape of an orbit conveys much information. The easiest case is that of a perfect circle, but as we all know, nature doesn’t deal … Read More

An elliptical orbit is defined by its size: the semi-major axis. This are the average distance of a satellite to the body around which it … Read More

Imagine how an object orbits. Think off throwing a baseball. Throw it hard, and it arcs to the ground. Throw it even harder, and it … Read More

Light will show you things (but so too will the dark). You can learn much about the universe from the night sky. Each galaxy and … Read More

When you point your telescope to some distant galaxy, what you see isn’t what it is; it’s what it was. And that difference, between when … Read More

Maybe you picture the universe like a stage with stars and planets sitting still while you travel about among them. Instead, idea of expansion revealed … Read More

The beauty of Hubble’s idea, which was surprisingly elegant, was this: The more distant a galaxy is, the further away it moves; and all those … Read More

That’s where Redshift comes in. It is sort of like Doppler shift, except instead of moving closer or farther from an object, we’re stretching out … Read More