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Star brightness versus star luminosity

Some extremely large and hot stars blaze away with the luminosity of a million suns! But other stars look bright only because they’re near Earth.

Gemini? Here’s your contellation

How to see the constellation Gemini in the night sky, plus some of ancient lore about the legendary Twins.

Got 5 minutes? Learn to see Saturn

June, July and August are especially good months for viewing Saturn in 2017. But you can find it this month, too, especially when the moon sweeps past on February 19, 20 and 21.

Valentine’s Day

Astronomer Guy Ottewell reflects on the planet of love.

Green Comet 45P: Photos and video

Green Comet 45P has been in our sky for months and passed closest on February 11, 2017. It’s a faint one, but intrepid astronomers have captured some wonderful images!

See it! February 10-11 lunar eclipse

A penumbral eclipse is subtle, but has a quiet beauty all its own. Thank you to all who submitted photos of the February 10-11, 2017 eclipse!

What’s a penumbral eclipse of the moon?

During a penumbral eclipse, observant people in the right spot on Earth will look up and notice a dark shading on the moon’s face. Others look and notice nothing at all.

How many eclipses in 1 calendar year?

Every calendar year has at least 4, but 5, 6 or even 7 eclipses are also possible. Why don’t we see them all?

Possible to have 3 eclipses in 1 month?

In 1 calendar month, 3 eclipses are rare. But in 1 lunar month, 3 eclipses are are more common. From 2000-2050, it happens 14 times.

What’s a Blood Moon?

Nowadays, 4 totally eclipsed moons in a row are called Blood Moons. Why? We don’t know for sure, but the answer may lie in a 2013 book by 2 Christian pastors.

What is retrograde motion?

Retrograde motion of Jupiter or Mars or Saturn in our sky is an illusion, caused by Earth’s passing these slower-moving outer worlds. But there’s a real retrograde motion, too.

Circumpolar stars never rise or set

From Earth’s North and South Poles, all the stars appear as circumpolar. Meanwhile, at the equator, no star is circumpolar. And what about in between?

Two stars in Scorpius are harbingers of spring

Go ahead. Treat yourself to something beautiful, and hopeful: a glimpse of two stars that represented a Pawnee version of Groundhog Day.

Groundhog Day has roots in astronomy

Groundhog Day is tied to the movement of Earth around the sun. It’s the year’s first “cross-quarter” day.

EarthSky’s guide to the bright planets

Venus at its brightest as the evening “star,” outshining nearby Mars by leaps and bounds. Plus see Jupiter rising before midnight, Saturn well up before dawn and Mercury closer to the sunrise.

When is the next Blue Moon?

Blue-colored moons are rare. But folklore has defined 2 other Blue Moons, too, which are more commonly seen. The next one will be 1 year from today.

Lengths of lunar months in 2017

Lunar months vary in part because the moon’s orbit around Earth isn’t a perfect circle. Longest (and shortest) lunar months in 2017, here.

Sun's path through the zodiac.

Ecliptic traces the sun’s path

The ecliptic is an imaginary line that marks the path of the sun. The signs of the Zodiac come from the constellations that lie along this line.

Orion Nebula: Where stars are born

To find the Orion Nebula in your night sky, look below Orion’s Belt. Your eye sees it as a tiny, hazy spot. But it’s a vast region of star formation.

Favorite photos from this weekend

The EarthSky community on Facebook outdid itself posting photos over the weekend of January 20-22, 2017. Thanks, everybody! Editors’ picks here.