Enjoying EarthSky? Subscribe.

231,711 subscribers and counting ...


How long to travel to Alpha Centauri?

Read about star travel via conventional propulsion, warp drives, and more.


What makes a red rainbow?

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.

Montauk Point lighthouse. Photo: Neeti Kumthekar

How can I capture star trails?

As Earth spins under the sky, the stars appear to move. When a camera captures that movement, that’s called a star trail. Plus … an astrophotographer explains how he does it.

Photo Credit: wili hybrid

What gives rainbows their curved shape?

A rainbow isn’t a flat two-dimensional image on the dome of sky. It’s more like a mosaic, composed of many separate bits … in three dimensions.

Photo credit: Robbo-Man

What is earthshine?

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

Sun pillar photo by Shanna Dennis

What is a sun pillar, or light pillar?

Sun pillars, or light pillars, are shafts of light extending from the sun or other bright light source. They’re caused by ice crystals drifting in Earth’s air.


Why beware the Ides of March?

What are the Ides of March? We in modern times probably wouldn’t know, if it weren’t for William Shakespeare.

Our local star.  Image via NASA

Are a star’s brightness and luminosity the same thing?

A star’s luminosity is its true brightness. Nearly every star you see with the unaided eye is more luminous than our sun.

Photo Credit: NASA

Are solar eclipses more common than lunar eclipses?

It’s sometimes said that, on a worldwide scale, solar eclipses outnumber lunar eclipses by about a three to two margin. True?

Eclipses for Beginners

Why no eclipse every full and new moon?

This year, in 2016, there are 12 full moons and 13 new moons, but only four eclipses – two solar and two lunar.