OVERVIEW The Sun warms Earth and lights our days but what is a sun A sun is a star that is the center of a solar system All suns are stars but not all stars are suns because some stars exist without planets surrounding them A sun is a star that has planets surrounding it Our Sun is one of many in the universe 4
A star is a hot sphere of gases that gives off energy in the form of light and heat Our Sun is one of many stars in the universe Scientists have theorized that there are at least 10 billion galaxies in the universe In our galaxy alone the Milky Way there are about 200 billion stars THINK ABOUT IT MEANOR A Most solar systems have two or more Only a few thousand stars What would stars all from our own a sunrise be like galaxy are visible to the with two suns naked eye The Andromeda galaxy can also be seen but it appears like a single star
STAR LIGHT STAR BRIGHT Stars vary in color from blue to yellow to red Blue stars are hotter than red stars and yellow stars are in the midrange Hotter stars tend to be brighter than cooler stars However the size of a star also affects the brightness Red giants and supergiant stars are relatively Proxima Centauri shown here through the Hubble Space Telescope is our closest neighboring star Because it is small and dim it is invisible to the naked
cool but bright because of their size The diameter of a supergiant can be IOo times that of the Sun In contrast a white dwarf is hot but dim because it is small Our Sun a yellow star is in the midrange of size and brightness THINK ABOUT IT HP 56948 a star 200 light years away from Earth has the same mass temperature and chemical composition as our Sun Scientists wonder if it has a planet in its solar system similar to Earth What might this other Earth be like All stars are big and hot but some are bigger or hotter than others I Our Sun is in the average range of heat and
