Enjoying EarthSky? Subscribe.

231,530 subscribers and counting ...

Adrian Strand captured this photo on a beach in northwest England.

Watch for earliest sunsets before solstice

Year’s shortest day comes at winter solstice. But, for Northern Hemisphere, earliest sunsets happen around early December. Southern Hemisphere? Your earliest sunrises are around now.


How long to orbit Milky Way’s center?

One journey of our sun and planets around the center of our Milky Way galaxy is sometimes called a cosmic year. That’s approximately 225-250 million Earth-years.

Sun halo captured on June 6, 2016 by Amy Gray in Aiken, South Carolina.

Why a halo around the sun or moon?

A large ring or circle of light around the sun or moon is called a 22-degree halo by scientists.

Photo by Rebecca Lacey in Cambridge, Idaho

What is a supermoon?

Are supermoons hype? In our opinion … no, just modern folklore. And they cause real physical effects, such as larger-than-usual tides.

Brocken Spectre via Micheal Burke.

What is the Brocken Spectre?

The Brocken Spectre is your own shadow, cast on mists below you, when you are mountain climbing. The shadow may appear enormous and has a ring around it.

Earth's shadow and full moon rising via Birgit Boden.

When can you see Earth’s shadow?

You can see it any clear evening …

As the sun sets one the stark Martian landscape, stars come into view. Will future Mars colonists have a North Star to guide them? Image via NASA.

Does Mars have a North Star?

Earth’s north star – Polaris – is located nearly directly above Earth’s north pole. There’s a star above Mars’ north pole, too, but it’s very faint.

Our friend Dave Walker in the UK caught another iridescent cloud in 2013. He wrote, "There's been a lot of very high cloud recently, always a cue for me to look out for more atmospheric optics."

What causes rainbow colors in clouds?

Iridescent clouds – clouds with rainbow colors – happen when especially tiny water droplets or small ice crystals individually scatter light.

Photo Credit: NASA

What is the sun’s proper name?

You’ve no doubt heard star names such as Polaris or Betelgeuse. But what about our star? Does the sun have a name, and if so what is it?


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.

Sliding stone at Racetrack Playa via Chris Tinker

What causes Death Valley’s sailing stones to move?

People used to think that strong winds – which can reach 90 mph in the Death Valley desert – caused the rocks to move. In fact, that’s not what happens.