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FAQs

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.

Can sharks smile? Do they even feel happy?

The Discovery Channel’s Shark Week is coming up (starts August 10) and sharks are on our mind ….

Attributing emotions to animals is almost irresistible to most people, and some animals do seem to show happiness, anger, fear, and other feelings. Dogs, cats, dolphins, and monkeys can be especially expressive. So … how about sharks?

Will the Andromeda galaxy someday collide with our Milky Way?

Image Credit: NASA, ESA et al.

This image represents Earth’s night sky in 3.75 billion years. The Andromeda galaxy (left) will fill our field of view then, astronomers say, as it heads toward a collision with our Milky way galaxy. Image Credit: NASA, ESA et al.

It’s a question people ask us… Will our home galaxy someday collide with the next-nearest spiral galaxy, in the direction of the constellation Andromeda? And if so, when?

Does Earth have a second moon?

Image of Earth with two moons, generated in Celestia software, by Grebenkov in Wikimedia Commons.

Many planets in our solar system have more than one moon. Mars has two moons, Jupiter has 66, Saturn 62, Uranus 27, Neptune 13. But our planet Earth has just one moon. Doesn’t it?