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Moon and Spica

February 26, 2016

For the light from the star Spica, it’s been a long journey. It began about 250 years ago — around the year 1766. By then, the American colonists were getting angry at their rulers in England, but were still a decade away from declaring independence. Parliament repealed an unpopular tax early in the year, briefly tamping down the fires of revolution.

Since then, the light from Spica has traveled about one-and-a-half million billion miles. To put it another way, if you were flying in a jet airliner at a steady speed of 500 miles per hour, it would take you more than 300 million years to cover that distance.

Spica’s light doesn’t take nearly that long to cross the interstellar gulf because it moves at, well, the speed of light — 670 million miles per hour. According to Albert Einstein’s theories of relativity, nothing can move faster than that.

As the light races toward Earth, some of it is absorbed by gas and dust between the stars. There’s not a lot between here and Spica, though, so most of the light is uninterrupted — it just keeps on cruising.

Spica stands close to the right of the Moon as they rise in late evening, and a little farther from the Moon at first light. And if you happen to look in that direction, some of the star’s light will end its journey across the galaxy by striking your eye — a journey that began on the surface of a brilliant star, and ended on a winter’s night on a planet 250 light-years away.

Script by Damond Benningfield

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