What is a star?
A star is a ball of hot gas. Stars are born in giant clouds. Stars look small because they are light years away from us. In fact, some of them are even bigger and hotter than our Sun. The stars can be cool and dim, cool and bright, hot and dim, and hot and bright. They can be blue, red, yellow, white, and orange.
Types of Stars
Stars has a size - tells how big or small a star is, luminosity - tells how bright or dim a star is, temperature - tells how hot or cool a star is, spectral class - a letter that tells the temperature of a star, type - tells what stage a star is in and color - tells the color of a star.
There are 4 types of stars: white dwarf, main sequence, giants, and super giants. White Dwarf - has old, small, mostly hot, and dim stars; Main Sequence - has middle age, medium, hot and cold, bright and dim stars; Giants - has middle age, large, bright, hot and cold stars; and Super Giants - has middle age large, bright, hot and cold stars.
H-R Diagram
H-R Diagram, which stands for Hertzsprung-Russel Diagram, is a graphical tool used by astronomers to classify stars based on their luminosity, spectral type, color,temperature, and evolutionary stage. This diagram also shows relationships and differences between stars.
In this diagram stars are represented by a dot. The position of each dot tells us two things about each star: its luminosity and its temperature. A star in the upper left of the diagram would be hot and bright. A star in the lower right of the diagram would be cool and dim.
Nuclear Fusion is a process when nuclear reactions inside a star change 2 hydrogen gas molecules in to a helium molecule. Nuclear reactions help star to born, because when the giant clouds of dust and gas - stellar nebula shrinks because of gravity, it becomes hotter and nuclear reactions start in the middle. Nuclear fusion creates an energy for a star.
The Life Cycle of a Star
All the stars are born in a giant clouds of dust and gas called Stellar Nebula. There are 3 types of stars: Sun-like stars, Huge stars, and Giant stars. Each of them have different cycle of life.
Sun-like stars start with stellar nebula, then it become red giant. After being a red giants, it become cloud of dust and gas called Planetary Nebula. After that, it become a white dwarf, then invisible object called black dwarf.
Huge stars starts with stellar nebula, then become a red giant. After that it explodes into supernova, and begin collapsing into neutron star.
Giant stars also start with stellar nebula, then become red giant. After that, it explodes in to supernova, and become a black dwarf.
