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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.

Why the night sky can tell us a fair bit about time. Photo: eArches National Park/Flickr

What is time?

… And why does it move forward?

From late January, and through mid-February, 5 bright planets were visible at once in the predawn sky. This image is from February 8, 2016.  It's by Eliot Herman in Tucson, Arizona.  View on Flickr.

See 5 bright planets at once

First time we can see 5 planets at once since 2005. All 5 are up before dawn, still, and all 5 will remain visible until Mercury disappears in the dawn just after mid-February.


How do snowflakes get their shape?

Depending on the temperature and humidity of the air where the snowflakes form, the resulting ice crystals will grow into a myriad of different shapes.