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Moon and Regulus

September 26, 2016

The Moon cozies up to a “dwarf” in the wee hours of tomorrow morning: Regulus, the brightest star of Leo, the lion. They’re well up in the east at first light, with Regulus close to the lower left of the Moon.

In astronomical jargon, terms like “dwarf” are relative. There are the tiny stars known as red dwarfs, the failed stars known as brown dwarfs, and the dead stars known as white dwarfs.

Most of the other stars are also known as dwarfs, although in a different way.

The main system for classifying stars uses the letters O, B, A, F, G, K, and M. The letters are based on the star’s color or surface temperature. The letter is followed by a number from zero to nine, breaking each class down into subcategories. And after that comes a Roman numeral from 1 to 5, with supergiants at the low end, then giants, subgiants, and dwarfs.

In this scheme, stars like Regulus and the Sun are classified as dwarfs, even though they’re bigger than most of the other stars in the galaxy. In fact, Regulus is about three times as massive as the Sun, and about four times wider. Only a few percent of the stars in the entire galaxy outrank it.

Dwarf stars are in the prime of life, converting hydrogen to helium in their cores. At the ends of their lives, when the hydrogen is gone, they’ll puff up like balloons — moving from the dwarf section of the scale to the giant section.

We’ll talk about the Moon and another bright morning light tomorrow.


Script by Damond Benningfield

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