The brightness of a star is called its magnitude, or size. Big stars are brighter than little stars, and so have greater absolute magnitude. Stars close to Earth also appear brighter than those farther away. They have greater apparent magnitude. Our sun appears to be the brightest star to us because it is the closest to Earth.
Stars have different colors, depending on how hot they are.
Very hot stars are blue, and the coolest stars are red. Usually, large stars are brighter and hotter. A group of celestial bodies traveling around a star is called a solar system, and the star in the center is called a sun. The sun and stars shine continuously, but the sun is seen only during the day and the stars are seen only at night. During the daytime, the light from the sun is so bright that the light from the stars is not noticeable.