R Trianguli 
Most of the life of a star like the Sun is pretty dull. It spends billions of years steadily “fusing” the hydrogen its core to make helium, releasing energy as it does so.
When the hydrogen runs out, though, the star undergoes a series of big changes that play out quickly on the astronomical timescale. A star known as R Trianguli, for example, is going through a phase that may last as little as a few centuries.
The star is puffing in and out like a beating heart — the result of the constant tug of war between radiation and gravity. The star is burning the hydrogen in a thin layer around its core. Radiation from that process heats the star’s outer layers and pushes them outward. As they expand, though, some of the radiation escapes into space, so the outer layers cool and fall back toward the core.
In R Trianguli, each of these “pulses” takes about nine months, and the results are spectacular. At its brightest, the star is more than 600 times brighter than at its faintest.
R Trianguli is losing a lot of its gas to space. Eventually, its outer layers will puff away, leaving only the star’s hot, dense core — a white dwarf.
The same fate awaits the Sun — in several billion years.
R Trianguli is in the eastern sky at nightfall, to the lower left of wedge-shaped Triangulum’s brightest star. At its brightest, the star is just visible to the unaided eye. Right now, though, it’s in the “fading” part of its cycle, so you’ll need a telescope to find it.
Script by Damond Benningfield, Copyright 2012