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Moon and Regulus

May 21, 2018

The first-quarter Moon snuggles especially close to a bright companion tonight. Regulus, the heart of Leo, the lion, will stand just a degree or so from the Moon as night falls — less than the width of your finger held at arm’s length. The Moon will pull away from the star later on, but they’ll still be quite close together as they set in the wee hours of the morning.

Their closeness is just an illusion — they just happen to line up in the same direction in the sky. In reality, they’re an extraordinary distance apart.

The Moon is a quarter of a million miles away. That’s a vast distance on the human scale, but the tiniest baby step by astronomical standards.

Regulus, on the other hand, is a bit more than 79 light-years away. In other words, traveling at the speed of light — about 670 million miles per hour — it takes light a bit more than 79 years to reach Earth. So a beam of light that leaves the surface of Regulus tonight won’t arrive at Earth until the year 2097. To put that in perspective, it’s just a few months longer than the life expectancy of a baby born in the United States. So we can truly say that Regulus is a lifetime away.

There’s a bit of uncertainty in the distance to any star. In the case of Regulus, it’s about seven-tenths of a light-year. That doesn’t sound like much until you consider this: That slight margin of error is equal to about 17 million times the distance to the Moon.

Script by Damond Benningfield

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