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Moon and Regulus

November 20, 2016

If you put your face close to the lamp next to your sofa, it looks pretty bright. But if you move back a few feet, the lamp loses most of its luster. Its bulb isn’t any dimmer — it just looks that way because of the greater distance.

The same thing is true of the stars. Some stars that look faint are actually just as bright as some of the ones that look bright, but they’re farther away.

You can see a good example of this in Leo. The lion’s brightest star, Regulus, stands just a whisker from the Moon as they climb into view after midnight.

A pattern that looks like a backwards question mark stretches to their upper left as they rise. The star at the end of the question mark’s loop is Epsilon Leonis.

It looks about one-fifth as bright as Regulus. But if you could place the two stars side by side, and add up all of their energy, Epsilon would be just as bright as Regulus. Regulus is hotter, so a given surface area emits more energy, but Epsilon is bigger, so there’s more surface to radiate light into space.

Both stars are more massive than the Sun, so the nuclear reactions in their cores take place at a much faster rate. Epsilon is the heavier of the two, so its reactions are fastest. Because of that, the star is closer to the end of its “normal” lifetime than Regulus, even though it’s tens of millions of years younger. It’ll soon shed its outer layers, exposing its hot, dead core — a tiny stellar light bulb with the wattage turned way down.


Script by Damond Benningfield

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