July 31st, 2015
Full Moon
Robert Bigelow

“Mister” Sol’s neighborhood

The New Horizons spacecraft is on its way to Pluto. It left Earth back in January 2006. Now it is almost halfway between the orbits of Saturn and Uranus. When will it reach Pluto? Not until July 2015. Why so…

Seth Jarvis

Planets Galore!

There’s an AP news story out today about astronomers announcing the discovery of 32 new planets orbiting stars other than our Sun.  That’s quite a number for a single announcement! I keep a little dashboard widget from NASA on my…

Seth Jarvis

Why are planets spherical?

Anthony Garcia wrote in to ask, “Why are planets perfect spheres, or at least appear to be perfect?” Nature loves spheres. It can’t get enough of them.

Seth Jarvis

Cosmic Quiz Winner

This week’s cosmic quiz question was submitted by Daniel Wallace, who asked, “How do astronomers figure out the size of planets orbiting other stars (and even what their atmosphere is made of)?”

How Big? A look at figuring size and scale

A few days ago, I needed to increase the size of an astronomical table to make it easier for my aging eyes to read. It was about half the size of a standard sheet of paper, so I decided to…

What is dark matter?

The short answer is no one really knows. Dark matter is a name given to something that, so far, has only been detected by the gravitational force that it exerts on visible matter and light. In fact, that gravitational force…

What is gravity?

A common answer to a child’s question of “Why do things fall?” is, “Because of gravity.” But knowing the name of something does not mean that we understand it. Originally, “gravity” was simply the built-in tendency of most objects to…

What is the Doppler Effect?

Stand on the sidewalk and listen to the sound of a car as it approaches and passes by. You will notice that the pitch of the sound is higher as the car approaches and then becomes lower as it moves…