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Christopher Crockett

What is a parsec?

Why do professional astronomers speak of distances in the universe not in terms of light-years, but in terms of parsecs, a distance of 3.26 light-years? Explanation here.

What is a coronal mass ejection?

Want to brush up on your knowledge about these solar hiccups – CMEs, for short – that can ripple through our solar system and can interrupt satellites and power grids on Earth?

What is the electromagnetic spectrum?

The electromagnetic spectrum describes all the wavelengths of light. From dark nebulae to exploding stars, it reveals an otherwise invisible universe.

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.

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.

What is the zodiac?

You might associate the word zodiac with astrology, but it has an honored place in astronomy, too. It’s defined by the annual path of the sun across our sky.

Gamma ray burst

What are gamma ray bursts?

Only the most powerful explosions in the universe.

What is a light-year?

Hint: A light-year is a unit of distance, not time.

Eta Carinae

Wolf-Rayets are the most massive and brightest stars known

Wolf-Rayet stars make our sun look tiny. They can be hundreds of times more massive, millions of times brighter, and tens of thousands of degrees hotter.

Elliptical galaxy ESO 325 G004

What are elliptical galaxies?

Elliptical galaxies are among the largest single star systems in the universe and are built by the collisions of many smaller galaxies.