What Is an Object in the Sky?

What Is an Object in the Sky? — page 3
STARS Stars are glowing balls of gases They are grouped into galaxies The Milky Way galaxy alone contains hundreds of billions of stars Most stars are incredibly far away Nearly all stars are mostly made up of a gas called hydrogen A star's core is very hot Great pressure squeezes the core causing some of the hydrogen to change into another gas helium This process makes the star shine a Stars are found in large groups called galaxies Galaxies I can contain billions of