More than 100 billion stars exist in our galaxy, yet on a clear night, only about 3,000 of them are visible to the naked eye. Keep reading to learn all about these magical night sights!
Star Bright
- A bright star, as seen from Earth, is either closer to us than other stars or produces more energy— or both.
- Astronomers rate star brightness by magnitude. Magnitude 1 is about 100 times brighter than magnitude 6.
- Stars with a magnitude of 6 or less can be seen with the naked eye.
- The brightest star seen from Earth, Sirius, is magnitude –1.46.
Not All Stars are White!
The color of a star indicates the temperature at its surface. The hottest stars are blue. The coolest stars are red. (Think of a candle flame. The hottest area is blue!) Astronomers have sorted star colors into classes. More stars are red than any other color.
How Stars Are Born
Stars form in dense billows of gas and dust particles called GIANT MOLECULAR CLOUDS. Gravity constantly pulls the particles together, while pressure constantly pushes them apart until the molecular cloud cools. The particles then gather into clumps called PROTOSTARS.
Gathering creates heat, and some protostars become so hot that they release energy (a process called thermonuclear fusion). This gathering and releasing balances a protostar, and it begins evolving into a star like the Sun.
A protostar that is too small to become a star is called a BROWN DWARF. It produces heat for a few million years.
Fading Stars
When stars run out of fuel, they die. How this happens depends on their mass. A WHITE DWARF is a small, dense, dying star that releases an expanding gas shell called a PLANETARY NEBULA. Stars the size of the Sun will eventually become white dwarfs. Scientists think that white dwarfs become BLACK DWARFS. A black dwarf star emits no light. (There are no known black dwarfs in the universe.)
A large star can collapse in an explosion called a SUPERNOVA when it dies. (When a hypergiant does this, it’s called a HYPERNOVA.) Gas and debris are violently ejected, and the core of the star shrinks into a NEUTRON STAR.
A neutron star is small (6 to 12 miles wide) but dense: One teaspoonful of a neutron star would weigh as much as a small mountain on Earth. A neutron star spins very fast—as much as hundreds of times per second.
A PULSAR is a type of neutron star that emits energy in pulses, sort of like a light beam from a lighthouse. When a massive star dies and collapses, it can form a STELLAR BLACK HOLE. The gravity of a black hole is so strong that it even pulls in light.