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FAQs

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.

What is a sun pillar, or light pillar?

U.S. West Coast got an amazing sun pillar on the first evening of spring. Thanks, Lyle Evans

The U.S. West Coast got an amazing sun pillar on the first evening of spring. Thanks, Lyle Evans!

EarthSky Facebook friends occasionally post beautiful photos of sun pillars, or light pillars. For example, there was a beautiful one seen from the U.S. West Coast on March 20, 2016 … a beautiful prelude to the first full night of spring. Click inside to learn what makes them, and for more photos.

Why beware the Ides of March?

Image credit: veraukoion

Image credit: veraukoion

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.

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

This Renaissance woodcut is called Empedocles Breaks through the Crystal Spheres.

This Renaissance woodcut is called Empedocles Breaks through the Crystal Spheres.

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.

Are solar eclipses more common than lunar eclipses?

Image by Joshua Valcarcel via Wikimedia Commons

Image by Joshua Valcarcel via Wikimedia Commons

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

Why no eclipse every full and new moon?

Photo credit: pizzodisevo

A solar eclipse happens at the new moon – when the moon passes between the sun and Earth. A lunar eclipse happens when the Earth, sun and moon align in space, with Earth in the middle. Why aren’t there eclipses at every full and new moon?

What causes Death Valley’s sailing stones to move?

The video above shows a famous sliding stone of Death Valley’s Racetrack Playa in motion. See it? It’s the big rock in the foreground.

Although their tracks across Racetrack Playa – a dry lake bed in Death Valley – have been observed and studied since the early 1900s, no one had ever seen the stones in motion … until recently. What’s more, the researchers who captured this video say they now know what causes the stones to move.