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FAQs

What are cloud streets?

cloud-streets-bering-sea-20jan2006-540

Cloud streets over the Bering Sea on January 20, 2006. Image Credit: Jesse Allen, NASA.

Your Friday FAQ. Find out what they are and how they form. And check out these cool images!

What is a supermoon?

What most call a Blue Moon isn't blue in color. It's only Blue in name. This great moon photo from EarthSky Facebook friend Rebecca Lacey in Cambridge, Idaho.

Moon photo is from Rebecca Lacey in Cambridge, Idaho.

It’s a super Harvest Moon in 2014. A few years ago, we in astronomy would have called it a perigean full moon – that is, a full moon closely coinciding with perigee, the moon’s closest point to Earth in its orbit. But, like almost everyone else, now we enjoy calling them supermoons. This post explains what a supermoon is, how many occur in 2014, which moon is the most “super” of all the 2014 supermoons (August 10), and gives a list of upcoming full supermoons for the years ahead.

What’s the birthstone for September?

The Logan Sapphire Brooch, the second largest sapphire known (at 422.99 carats), is on display at the National Museum of Natural History in Washington, D.C. Image Credit: Andrew Bossi

The Logan Sapphire Brooch, the second largest sapphire known (at 422.99 carats), is on display at the National Museum of Natural History in Washington, D.C. Image Credit: Andrew Bossi

Happy birthday to all you September babies!

Your birthstone, the sapphire, was said to represent the purity of the soul.

What is the blue hour?

Blue hour by Marianna Bucina Roca in Gloucester, Massachusetts.

Blue hour by Marianna Bucina Roca in Gloucester, Massachusetts.

When you see a strong blue tone to photographs, it could be that the photographer has taken advantage of the blue hour. That’s a time of day when the sun has just set or is about to rise, when the sky overhead takes on a deep blue color, and when the landscape is suffused with bluish light. The blue hour is a good time to take photos of the moon, because then the moon’s glare isn’t so bright in contrast to the sky. It’s also a good time to take landscape photos, as the photos in this post show.

What makes a red rainbow?

Göran Strand of Sweden captured this double red rainbow.  Used with permission.

Photo by Göran Strand. Used with permission.

Astrophotographer Göran Strand of Sweden kindly gave us permission to publish this photo, which a phenomenal double red rainbow. Details … inside.

How far is a light-year?

The Orion Nebula, 1,500 light years from Earth. Image credit: NASA/JPL-Caltech/STScI

The Orion Nebula, 1,500 light years from Earth. Image credit: NASA/JPL-Caltech/STScI


Here’s your FAQ for this Friday ….

Light is the fastest-moving stuff in the universe. It travels at an incredible 300,000 kilometers (186,000 miles) per second. That’s very fast. A light-year is the distance light travels in one year. How far is that?

How to see a green flash

San Diego, California on October 25, 2012, taken by EarthSky Facebook friend Jim Grant.  Thanks Jim!

San Diego, California on October 25, 2012, taken by EarthSky Facebook friend Jim Grant. Thanks Jim!

It’s said that once you’ve seen a green flash, you’ll never go wrong in matters of the heart. Here’s all you need to know to see the legendary green flash, plus great pics.

Video: Why does the moon look so big on the horizon?

The August 10 supermoon might look super big seen near a horizon. But all full moons look big near a horizon, due to an illusion called the moon illusion.

What’s the birthstone for August?

Peridot

Peridot

Happy birthday to our August friends! This is one of your birthstones, peridot. Your other birthstone is sardonyx.

Read about both your birthstones….

How to see anticrepuscular rays

View larger. | Anticrepuscular rays - seen in the east at sunset - in Nevada.  Shreenivasan Manievannan posted this photo on EarthSky Facebook in July 2014.  Visit Shreeniclix Photography.

Anticrepuscular rays – seen in the east at sunset – in Nevada. Shreenivasan Manievannan posted this photo on EarthSky Facebook in July 2014.

Next time you see crepuscular rays or sunrays extending from the horizon … turn around. You might catch a glimpse of elusive anticrepuscular rays.