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FAQs

Why don’t planets twinkle like stars do?

If you could see stars and planets from outer space, both would shine steadily. But – from Earth – stars twinkle while planets shine steadily. Why?

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 is coming up on the night of April 14-15, 2014. This total eclipse of the moon will be visible from the Americas. We in astronomy had not heard the term Blood Moon used in quite this way before this year, but now the term is becoming widespread in the media.

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.

Why is Mars sometimes bright and sometimes faint?

In April 2014, Mars and Earth will be on the same side of the sun.  Earth will be passing between the sun and Mars.   Image via Fourmilab.

In April 2014, Mars and Earth will be on the same side of the sun. Earth will be passing between the sun and Mars. April is the best month in 2014 for viewing Mars. Image via Fourmilab.

Mars is the world orbiting the sun one step outward from Earth’s orbit. Earth takes one year to orbit the sun once. Mars takes about two years. The orbits of Earth and Mars are the reason Mars is one of the most fascinating planets to watch in our sky, and they are the reason Mars is sometimes bright and sometimes faint. On April 8, 2014, Earth goes between the sun and Mars. That’s why Mars is so bright this April.

The brightness of Mars in our sky depends on where our two planets are in orbit around the sun. Sometimes Earth is close to Mars, and sometimes we are far away.

We are relatively close – and Mars appears at its brightest in our sky for that two-year period – every time Earth passes between the sun and Mars. That’s what’s happening today.

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.