The sun consists largely of hydrogen gas. Its energy comes from
nuclear fusion of hydrogen to helium.
There are essentially two types of planets in our
The four inner (terrestrial) planets consist mostly of:
Four of the outer planets are gas giants, consisting of :
thick outer layers of gaseous materials, perhaps with a small rocky core.
The fifth outer planet Pluto has an unknown composition, and appears
Moons are natural satellites of planets that vary widely in
Comets orbit the sun and consist mostly of
Asteroids are rocky or metallic iron objects ranging in size from millimeters to kilometers. They are the source of
Much of our knowledge about the solar system is
a result of space exploration efforts. These efforts continue to improve our understanding of the solar system.
was the first manned landing on the moon.
The Big Bang Theory
states that the universe began as a dense sphere that expanded and eventually condensed into galaxies.
The solar nebular theory
explains that the planets formed through condensing of the solar nebula.
Stars form by
condensation of interstellar gas.
are collections of large numbers (billions) of stars. The sun is in the Milky Way galaxy.
The solar system
is located in the Milky Way Galaxy.
The basic types of galaxies are :
spiral, elliptical, and irregular.
is the distance light travels in one year and is the most commonly used measurement for distance in astronomy.
The Hubble Space telescope
has greatly improved our understanding of the universe.