The California Nebula is a cloud of interstellar gas set aglow by radiation from nearby hot stars. The cloud's outline resembles that of the state of California. It is about 1,500 light-years away, in the constellation Perseus. The nebula spans dozens of light-years. [Caltech/Palomar Observatory/DSS]
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As anyone who’s looked at the clouds passing overhead on a pleasant autumn afternoon can tell you, it’s easy to see shapes in them. And the same thing is true with the clouds of gas and dust sprinkled through the galaxy. One well-known example is the California Nebula. It really does look like the outline of the Golden State — except that it’s red rather than gold.
The red color actually comes from a blue star, known as Xi Persei. The star is so hot that it emits lots of ultraviolet radiation. Some of this energy strikes atoms of hydrogen gas that make up most of the nebula. That rips the hydrogen’s proton and electron away from each other. The two may later rejoin. As the electron settles into position, it emits red light — the glow that colors the nebula.
The nebula is about 1500 light-years away, in the constellation Perseus, which is low in the northeast at nightfall, and high in the east by the time the Moon sets around midnight.
Even though the nebula spans dozens of light-years, it’s just a small part of a much larger cloud of gas and dust. Normally, such clouds spawn new stars. For some reason, though, this cloud is producing very few. In fact, it didn't even make the blue star that causes the nebula to glow. Instead, that star was born elsewhere, and it’s simply passing near the nebula.
Someday, though, this mostly dark cloud may begin making large numbers of stars — lighting up Perseus, but obliterating the outline of the California Nebula.
Script by Ken Croswell, Copyright 2016