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Moon and Regulus

November 1, 2018

In the original “Star Wars” movie, Han Solo brags that his ship, the Millennium Falcon, can make the Kessel run in less than 12 parsecs. Since a parsec is a unit of distance, not time, that didn’t seem to make any sense. But in “Solo,” the most recent movie, it’s explained that the Kessel run isn’t a straight path — it maneuvers around several objects along the way. A good ship and a good pilot, though, can take a dangerous shortcut — and cut the distance down to about 12 parsecs.

While the Kessel run is fictional, the parsec isn’t. In fact, it’s the most commonly used unit of distance in modern astrophysics. It measures the distances to objects beyond the solar system — stars, galaxies, and others. It’s equal to about three and a quarter light-years.

The word “parsec” is short for “parallax second.” It’s based on the apparent motion of an object as Earth moves from one side of the Sun to the other. As a result of that shift, the viewing angle to an object changes over the course of a year. How much it changes reveals the object’s distance. The angles are so tiny, though, that the technique works best for objects that are within a few thousand parsecs.

A star whose distance is easily measured with the technique is in good view early tomorrow: Regulus, the bright heart of Leo. It’s close to the upper right of the Moon at first light. The best measurements to date say the star is about 79 light-years away — just 24 parsecs.

Script by Damond Benningfield

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