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Ask Dr. Universe orbit
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Why can we sometimes see the moon during the day? – Eli, 7, Texas

Dear Eli,

I love to go for a walk with my dog roommate. Sometimes we see the moon in the sky—even though it’s daytime.

I asked my friend Michael Allen why that happens. He’s an astronomer at Washington State University.

He told me that we have to ask “what is a day” to answer your question.

“The sun lights up the earth,” Allen said. “Since the earth is a round ball, only half of the ball can ever be lit up at any one time.”

The side of the earth that the sun shines on experiences day. The side that faces away from … » More …

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Does the sun orbit anything? – Kingston, 11, Illinois

Dear Kingston,

When we think about orbits, we usually picture the Earth zooming around the sun. But does the sun just sit there? Or is it on its own journey?

I asked my friend Guy Worthey. He’s a space scientist at Washington State University.

He told me that an orbit happens because the gravity from something big pulls on a moving object. The sun has lots of gravity because it’s ginormous compared to Earth. So, that gravity pulls on the Earth and holds us in orbit.

But our sun isn’t the only star. It’s one of many, many stars in the Milky … » More …

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