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FAQs

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?

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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?

How do astronomers know the mass of Jupiter?

This true-color simulated view of Jupiter is composed of 4 images taken by NASA's Cassini spacecraft on December 7, 2000.

This true-color simulated view of Jupiter is composed of 4 images taken by NASA’s Cassini spacecraft on December 7, 2000.

Jupiter is the largest planet in our solar system and boasts of more than twice the mass (heaviness) of all the other solar system planets, dwarf planets, moons and asteroids combined. But how do astronomers even begin to know Jupiter’s mass?

How to watch a total eclipse of the moon

Total lunar eclipse mosaic by eclipse master Fred Espenak.   Visit his page for the April 14-14 eclipse.

Total lunar eclipse mosaic by eclipse master Fred Espenak. Visit his page for the April 14-14 eclipse.

Get ready to watch the total lunar eclipse on Monday night (April 14-15.) A total lunar eclipse is one of the most dramatic and beautiful – and easiest-to-view – of all astronomical events. During a total lunar eclipse, the sun, Earth and moon form a line in space. Earth’s shadow falls on the face of the moon. Click into this post to learn how to watch the eclipse.

What’s the birthstone for April?

Photo credit: Kim Alianz

Photo credit: Kim Alianz


Have a birthday this month? If yes … happy birthday! Your birthstone is the diamond, symbol of enduring love.

Diamonds’ cold, sparkling fire has held us spell-bound for centuries, inspiring rich, passionate myths of romance, intrigue, power, greed, and magic. Ancient Hindus, finding diamonds washed out of the ground after thunderstorms, believed they were created by bolts of lightning. Read more ….

What are star trails, and how can I capture them?

A two-hour-and-15-minute star trail image from March 21, 2014.  Our friend Ken Christison in North Carolina captured this image.  He wrote,

A two-hour-and-15-minute star trail image from March 21, 2014. Our friend Ken Christison in North Carolina captured this image. Want to see what a single frame of this image looked like? Click inside.

What are star trails? They are the continuous paths created by stars, produced during long time exposure photographs, as shown on this page. In other words, the camera doesn’t track along with the stars’ apparent motion as night passes (actually caused by Earth’s spin under the sky). Instead, the camera stays fixed, while, as the hours pass, the stars move. The resulting photos show the nightly movement of stars on the sky’s dome.

What is a Dyson sphere?

View larger. | Here is a completely fantastic artist's concept of a Dyson sphere.  I like it.  Notice the little moon on the left side, being ravaged for raw materials.  Via FantasyWallpapers.com

View larger. | A fantastic artist’s concept of a Dyson sphere. The image is called Shield World Construction, and it’s by Adam Burn.

Proponents of solar power know that only a tiny fraction of the sun’s total energy strikes the Earth. What if we, as a civilization, could collect all of the sun’s energy? If so, we would use some form of Dyson sphere, sometimes referred to as a Dyson shell or megastructure.

Can you explain why Earth has four seasons?

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Happy equinox!

Nearly everyone enjoys the change of seasons on Earth – from winter to spring, from summer to fall. But why do our seasons change?