The universe contains everything, ever. It is thought to have come into being by the "big bang" that somehow broke the known laws of physics. In essence, a super-dense particle suddenly expanded. Where the particle originated is a mytery answered only by speculation and/or metaphysics.
Of known laws of physics presumably broken, the chief of these is the law of gravity. This is to say, dense particles tend to collapse in on themselves at some point to create "black holes." After some unknown force caused the expansion the force of gravity is thought to have overcome the force of expansion in local pockets to form all the particular bodies and collectives seen today.
Meanwhile, the laws of physics also indicate that the universe is expanding at an accelerated rate, leading to an assumption of a size far greater than that which has been detected with the most powerful telescopes in existence. Once having determined that the earth orbits the sun, the distance to the local star was determined to be about 93 million miles. In an orbit among relatively stationary local stars, geometry has been used to determine vast distances between stars and, when discerned, galaxies. Based on assumptions hammered out among scientists over the years, the observable universe is a sphere -- from the viewers perspective -- with a radius of about 47 billion light-years (282 billion trillion miles). However, this is is based on measurements of expansion of visible things. Theoretically, the size is thought to be infinite.
Within this sphere, there are an estimated 100 billion galaxies with an average of around 30 billion stars each. Around many of these stars there revolve planets such as those in the local "solar system." These planets often are accompanied with moons. Interspersed in the local system, at least, are smaller bodies known as asteroids and comets. Smaller bits of material, which are mostly debris from deteriorating comets, often enter the atmospheres of the planets, mostly burning up before impact with the surfaces. Impacts do occur, though, as is readily visible upon the earth's moon.
The most familiar galaxy is the Milky Way which includes the Solar System; The Solar System consists of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
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