Enjoying EarthSky? Subscribe.

206,818 subscribers and counting ...

FAQs

How long would it take to get to Alpha Centauri?

Credit: Mark Rademaker/Mike Okuda/Harold White/NASA.

What a spaceship with warp drive might look like. Credit: Mark Rademaker/Mike Okuda/Harold White/NASA.

Alpha Centauri is the nearest star system to our sun at 4.3 light-years away. That’s about 25 trillion miles (40 trillion km) away from Earth – nearly 300,000 times the distance from the Earth to the sun. How might we travel to Alpha Centauri, the next-nearest star? And how long would it take to get there? Read about star travel via conventional propulsion, warp drives, and more.

What makes a red rainbow?

Frances Pelletier caught this double red rainbow - and the planet Venus - on February 9, 2016 from Myrtle Beach, South Carolina.

Frances Pelletier caught this double red rainbow on February 9, 2016 from Myrtle Beach, South Carolina.

Red rainbows happen when the sun is on the horizon. They’re created in much the same process that causes a sunset or sunrise to look red. Details – and more photos – inside.

What are star trails? How can I capture them?

Montauk Point lighthouse. Photo: Neeti Kumthekar

Montauk Point lighthouse. Photo: Neeti Kumthekar

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.

Why is 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 in 1970.  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

April 22, 1970 – Arbor Day – was the first Earth Day. Today, a common practice in celebration of Earth Day is still to plant new trees.

Mars is getting bright! Here’s why

Earth will between between the sun and Mars on May 22, 2016.  Then, the distance between our two worlds will be at its least for this two-year period, and Mars will appear brightest in our sky.  Image via Fourmilab.

Earth will pass between between the sun and Mars on May 22, 2016. Then, the distance between our two worlds will be at its least for this two-year period, and Mars will appear brightest in our sky. Image via Fourmilab.

We’ll pass between Mars and the sun just one month from today, on May 22. Watch Mars brighten dramatically between now and then!

What gives rainbows their curved shape?

View larger. | Photo taken January 10, 2016 by Jennifer Khordi.

Photo taken January 10, 2016 by Jennifer Khordi.

A rainbow isn’t a flat two-dimensional image on the dome of sky. It’s light along a three-dimensional cone, with your eyes at the tip.

What is a glory?

Photo by Judy Sweeny. It's an airplane glory - shadow of the plane with a halo of light around it - which she took out the window flying from Addis Ababa to Dubai.

EarthSky Facebook friend Judy Sweeny captured this glory from an airplane window in March 2015, while flying from Addis Ababa to Dubai.

Glories are common. They’re seen all the time by people traveling in airplanes. You need the sun to be directly behind your head. In front, you need an ordinary cloud. As you look toward the cloud, look for the shadow of the airplane. The plane’s shadow may be surrounded by a multi-colored circle of light. That’s the glory.

What is earthshine?

The moon and Venus over  North Carolina by Ken Christison.

The moon and Venus over North Carolina by Ken Christison.

That glow over the unlit part of a crescent moon – called earthshine – is light reflected from Earth.

Beautiful photos in this post!

Why does the moon seem to follow you?

Full moon photo by EarthSky community member Fernando Alvarenga in San Salvador.

Full moon photo by EarthSky community member Fernando Alvarenga in San Salvador.

You, or your kids, might notice this. When you’re moving in a car, earthly objects get left behind, but the moon seems to follow. Why?

Video: What is a pulsar?

A pulsar is a rapidly spinning neutron star which is the small, incredibly dense remnant of much more massive star. How dense? A teaspoon of matter from a neutron star weighs as much as Mount Everest.