StarDate: November 25, 2009

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The constellation Triangulum has only a couple of moderately bright stars -- and only one of those has a proper name. Mothallah -- a name that means "the triangle" -- stands halfway up the eastern sky at nightfall, at the tip of the skinny triangle.

The star is about half again as massive as the Sun. That doesn't sound like much, but it has a big effect on the rest of the star's vital statistics -- and its lifespan.

Astronomers have a couple of ways of measuring a star's mass. One way is to plot its brightness against its surface temperature. Heavier stars "burn" the nuclear fuel in their cores more quickly, so they shine hotter and brighter than their punier counterparts. Mothallah, for example, is several thousand degrees hotter than the Sun, and more than 10 times brighter. Plotting those numbers yields a mass of 1.5 times the Sun's mass.

There's a second way to measure mass, and it's more precise than the first.

If a star has a companion, you can measure the mass of both stars by plotting their orbit and applying some math. Fortunately, Mothallah has a small companion. Measurements of their mutual orbit confirm the estimate of one and a half times the mass of the Sun.

A star's mass also determines how long it will live. Since heavier stars use their nuclear fuel more quickly, they live shorter lives. Mothallah, for example, will live only around three billion years -- compared to more than 10 billion years for the Sun.

Script by Damond Benningfield, Copyright 2009

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