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FAQs

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.

What makes Venus the brightest planet?

Venus and the moon by EarthSky Facebook friend Mike O’Neal. Beautiful Mike!

Get up early and look for Venus in the predawn and dawn sky before sunrise. It’s bright! In fact, it’s the third-brightest celestial body to light up the heavens, after the sun and moon. Here’s why it’s so bright.

Can you explain why Earth has four seasons?

obliquity_wikimedia_400

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?

What do Phobos and Deimos look like from Mars?

Photo Credit: NASA

Photo Credit: NASA

The Martian moons are tiny. The larger moon, Phobos, is only about about 14 miles across. And Deimos is about half that size. They orbit Mars more closely than our moon orbits Earth, but because they’re so tiny they appear smaller than our moon does.

In fact, Deimos, the more distant moon, looks like a star in Mars’ sky. But it’s twice as bright as any star-like object seen in Earth’s sky. Deimos orbits at nearly the same speed Mars rotates – so it needs three Martian days to crawl from one side of Mars’ sky to the other. And, by the way, a day on Mars is about the same length as Earth’s day.

On the other hand, Phobos – the larger and closer of the two moons – zooms around Mars two and a half times every Martian day. Because it out-races Mars’ rotation, Phobos rises in the west and sets in the east. Phobos appears about a third as large in the Martian sky as our moon does in Earth’s sky.

What is a pulsar?

Today’s FAQ: What is a pulsar?

A pulsar is a rapidly spinning neutron star which is the small, incredibly dense remnant of much more massive star. A teaspoon of matter from a neutron star weighs as much as Mount Everest. This cool video from NASA Astrophysics explains it well.

What are the Ides of March, and why beware them?

Beware-the-ides-of-March-730709

Today is the Ides of March. Happy Ides!

If you have heard of the Ides of March, you know you’re supposed to beware them. Why? In ancient Rome, the ides of March were equivalent to our March 15th. You probably know of the Ides of March thanks to William Shakespeare. In his play Julius Caesar, a soothsayer – or fortune teller – says to Caesar: Beware the Ides of March.

Stellar luminosity: The true brightness of stars

Image credit: NASA

Image credit: NASA

When we talk about the luminosity of a star, we are referring to the star’s intrinsic brightness. We are not talking about the star’s apparent magnitude – its brightness as it appears from Earth.

For instance, most every star that you see with the unaided eye is larger and more luminous than our sun. The stars that we see at night are millions – even hundreds of millions – of times farther away than the sun. Regardless, you can still see these distant suns because many of them are hundreds or thousands of times more luminous than our local star.