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EarthSky

Clouds that look like waves in the sky

Clouds in the sky can sometimes look like ocean waves. These photographic clouds are called Kelvin-Helmholtz clouds, and occasionally also go by the name billow clouds or shear-gravity clouds.

Why not an eclipse at every full and new moon?

If the moon orbited Earth on the same plane that Earth circles the sun, then we'd have a total lunar eclipse at each full moon, and a total solar eclipse at each new moon. But that doesn't happen because the lunar orbit is inclined to Earth's orbit by about 5 degrees.

Listen: Have aliens already visited us?

A podcast featuring Harvard theoretical physicist Avi Loeb, on the subject of whether 'Oumuamua - the strange object that swept through our solar system in 2017 - is an artifact of an alien intelligence.

Photos of the supermoon, April 2021

The first of 2 spring supermoons in 2021 took place on April 26 or 27 (depending on your location on Earth). We received many wonderful submissions from you, our readers. Here's a gallery of some favorites. Thanks to all who submitted!

When is the next tide? Recommended almanacs here

The EarthSky-recommended tide almanacs listed here are based on astronomical influences on the tides. They'll help you in finding the next high and low tides.

Sunlight through trees in Singapore

When sunlight filters through trees, you may get a corona effect where the rays from the light sources take on the colors of the rainbow.

Before they disappear, watch for Orion and Sirius

Orion the Hunter is one of the sky's most noticeable constellations. Sirius is the sky's brightest star. As Earth revolves around the sun, they're both about to disappear for awhile. Here's how to star hop from Orion's Belt to Sirius.

Use the Big Dipper to find the Little Dipper

Polaris - aka the North Star - marks the end of the Little Dipper’s handle. The 2 outer stars in the bowl of the Big Dipper always point to Polaris.

Is the Hyades star cluster being destroyed?

Data from ESA’s Gaia star-mapping satellite have revealed tantalizing evidence that the famous V-shaped Hyades - nearest star cluster to our sun - is being disrupted. The culprit may be a suspected population of dark matter sub-halos. Wow!

Follow the arc to Arcturus, drive a spike to Spica

If you only ever learn one star mnemonic, make it this one!