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March 14, 2022

It’s impossible to tell how far a star is just by looking at it. The star Xi Puppis, for example, is fairly bright. That might suggest that it’s close by. Instead, it’s probably about 1200 light-years away — a long distance for a naked-eye star.

It’s hard to comprehend just how far that really is. A light-year is the distance that light travels in one year. Since it moves at a zippy 670 million miles per hour, the miles add up. So the distance to Xi Puppis is about seven quadrillion miles — a seven followed by 15 zeroes.

A star that’s that far away has to be especially bright, and Xi Puppis is. When you add up all the forms of light it produces, it’s about 60 thousand times brighter than the Sun. It’s also much bigger and heavier than the Sun.

But looking at this brilliant star is more than just looking across a vast distance. It’s also looking back in time. It takes the star’s light 1200 years to cross that gulf, so we see the star as it looked 1200 years ago — around the start of the ninth century.

Xi Puppis is one of the brighter stars of the constellation Puppis. It represents the stern of the ship Argo, which carried Jason and the Argonauts on their adventures. It sails low across the south this evening. Xi Puppis is visible from most of the country, quite low in the south at nightfall. It’s well to the lower left of Sirius, the brightest star in the night sky — just nine light-years from Earth.

Script by Damond Benningfield

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