To predict the lifespan of a star, you don’t need a crystal ball – a bathroom scale will do just fine. Heavier stars age faster, so if you know the star’s mass, you have a good idea of its future.

Consider Tarazed, the second-brightest star of the eagle. It’s only about six percent the age of the Sun. But because it’s about three and a half times the Sun’s mass, it’s already completed the “prime” phase of life. Now, it’s well into the next phase – as a red giant.

Mass is critical because, as the star’s mass increases, so does its gravity. Stronger gravity squeezes the star’s core more tightly, increasing its temperature. That revs up the rate of nuclear reactions in the core.

When a star is born, its core is mostly hydrogen. In the prime phase of life, the star “fuses” the hydrogen atoms to make helium. When the hydrogen is gone, the core shrinks, so it gets even hotter. That causes the star’s outer layers to puff up, which is what’s happened to Tarazed – it’s more than 90 times the Sun’s diameter.

Higher core temperatures trigger the next round of reactions. So today, Tarazed is fusing the helium to make heavier elements. Eventually, that will end as well. Tarazed will shed its outer layers, leaving only its tiny, dead core – ending the star’s fairly short but bright life.

Tarazed is low in the east at nightfall. It’s close above even brighter Altair, at the southern point of the Summer Triangle.

Script by Damond Benningfield