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FAQs

What is earthshine?

The moon and Venus over  North Carolina by Ken Christison.

The moon and Venus over North Carolina by Ken Christison.

If you’ve been looking at the moon shortly before sunrise, you might have noticed not only the bright crescent of the moon, but also the rest of the moon as a dark disc. That pale glow on the unlit part of a crescent moon is light reflected from Earth. It’s called “earthshine.”

Which spiral arm of the Milky Way contains our sun?

Our sun is located between two major spiral arms of the Milky Way galaxy, in what is sometimes called the Orion Arm or Orion Spur. Image updated in 2010 by R. Hurt via Wikimedia Commons.

We live in an island of stars called the Milky Way, and many know that our Milky Way is a spiral galaxy. In fact, it’s a barred spiral galaxy. But where within this vast spiral structure do our sun and its planets – our solar system – reside? In fact, astronomers say, we’re not located in one of the Milky Way’s primary spiral arms. Instead, we’re located between the Sagittarius and Perseus Arms of the Milky Way. Our local spiral arm is sometimes Orion Arm, or sometimes the Orion Spur.

Why do stars twinkle?

If you could see stars and planets from outer space, both would shine steadily. But – from Earth – stars twinkle while planets shine steadily. Hank Green of SciShow explains in the video above, and you can read more inside.

What is the electromagnetic spectrum?

Color spectrum via Shutterstock

Color spectrum via Shutterstock


When you think of light, you probably think of what your eyes can see. But the light to which our eyes are sensitive is just the beginning; it is a sliver of the total amount of light that surrounds us. The electromagnetic spectrum is the term used by scientists to describe the entire range of light that exists. From radio waves to gamma rays, most of the light in the universe is, in fact, invisible to us!

What is the sun’s proper name?

Our sun.  By any other name, it'd still be awesome.  Image via NASA.

Our sun. By any other name, it’d still be awesome. Image via NASA.

You’ve no doubt heard some star names such as Polaris the North Star – or Betelgeuse in the constellation Orion. But, although it’s also a star, our sun doesn’t have a generally accepted and unique proper name. It’s just the sun.

Earth and other planets in our solar system have their own names. Does the sun have a name?

Why more Eta Aquarid meteors in Southern Hemisphere?

Eta Aquarid meteor, by Ann Dinsmore, on May 5, 2013.

Eta Aquarid meteor, by Ann Dinsmore, on May 5, 2013.

Everyone around the globe can enjoy the Eta Aquarid meteor shower in early May. But it’s better viewed from the Southern Hemisphere than the Northern Hemisphere. Why? If you traced the paths of Eta Aquarid meteors backward on the sky’s dome, you’d find that these meteors appear to stream from an asterism, or recognizable pattern of stars, known as the Water Jar in the constellation Aquarius. The later sunrises in the Southern Hemisphere at this time of year let Aquarius rise higher into the predawn sky as seen from that part of the globe. More details inside this post.

Why do we celebrate May Day?

Happy May Day! May Day is an ancient spring festival in the Northern Hemisphere. It’s an astronomical holiday, one of the year’s four cross-quarter days, or day that falls more or less midway between an equinox and solstice – in this case the March equinox and June solstice. May Day also stems from the Celtic festival of Beltane, which was related to the waxing power of the sun as we move closer to summer. At Beltane, people lit fires through which livestock were driven and around which people danced, moving in the same direction that the sun crosses the sky.

What’s the birthstone for May?

shutterstock_72094480

Happy birthday to all you May babies! Your birthstone, the emerald, is a type of beryl colored green by chromium. Perfect emeralds are among the rarest of gemstones. Kings and queens wore emeralds in Babylon and Egypt, and Cleopatra owned them as part of her royal fortune. Later, in the Middle Ages, people believed that the emerald held the power to foretell the future. Find out more about emeralds, and the birthstones for all the months of the year.

What is a Blood Moon?

This is what a total eclipse looks like.  This is the total eclipse of October 27, 2004 via Fred Espenak of NASA, otherwise known as Mr. Eclipse.  Visit Fred's page here.

This is what a total eclipse looks like. This is the total eclipse of October 27, 2004 via Fred Espenak of NASA. Visit Fred’s page here. We astronomy writers often describe a totally eclipsed moon as appearing ‘blood red.’ Here’s why the moon turns red during a total eclipse.

The first Blood Moon eclipse in a series of four happened on the night of April 14-15, 2014. The next one will be on the night of October 7-8, 2014.

Why celebrate Earth Day on April 22?

In the late 1960s, there were love-ins, be-ins ... and, like the first Earth Day, teach-ins.  Here are two organizers of the first Earth Day.  Image via earthday2013funphotos.com

In the late 1960s, there were love-ins, be-ins … and, like the first Earth Day, teach-ins. Here are two organizers of the first Earth Day in 1970. Image via earthday2013funphotos.com

The first Earth Day – April 22, 1970 – marked the beginning of the modern environmental movement. Approximately 20 million Americans, especially on college campuses, participated. Since then, Earth Day is always celebrated on April 22. But why April 22?