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Christopher Crockett

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.

Aug 2012 CME

What is a coronal mass ejection or CME?

A CME can launch a billion tons of plasma from the sun’s surface into space, at speeds of over a million miles per hour. 

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.

Stellar parallax

What is a parsec?

Astronomers typically speak of distance in the universe in parsecs, not light-years. One parsec is about 30 trillion kilometers, or just over three light-years.

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.