4 NOT JUST ANOTHER STAR At its brightest the planet Uranus is just barely visible to someone on Earth looking up at the night sky So ancient astronomers could see Uranus but they could not tell that it was a planet In contrast the planets Mercury Venus Mars Jupiter and Sat urn are easily seen shining in Earth’s night sky to someone who knows where and when to look Astronomers could tell that these bright objects were planets by the way they moved People on Earth can barely see Uranus marked in green above without using a telescope
5 The planet Neptune was discovered after Uranus in 1846 That was less than two hundred years ago What else might we discover in another two hundred years THINK ABOUT IT After the telescope was invented in the early 1600s Uranus was seen several times Those who spotted it though thought Uranus was just another star Then in 1781 an English astrono mer named William Herschel discovered what he thought was a curious star or per haps a comet This unusual object soon proved to be a planet Uranus William Herschel built his own tele scopes using very large mirrors to ob serve the night sky
6 Like all the planets in the solar system Uranus orbits the sun Uranus is the seventh planet from the sun It is found between Saturn and Neptune Uranus is called one of the outer planets along with Jupiter Saturn and Neptune These are the planets that are found past the main asteroid belt in our solar system This illustration shows all the planets in Earthʼs solar system Uranus and the other outer planets orbit the sun beyond the main asteroid belt
7 VOCABULARY AU or astronomical unit is the unit of length scientists use to express distance in space It is equal to the average distance between Earth and the sun which is 93 million miles 150 million km Uranus travels around the sun at an average distance of about 1 8 billion miles 2 9 billion kilometers It is about 1 7 billion miles 2 7 billion km or 18 3 AU from Earth Nep tune the eighth planet from the sun is about 1 billion miles 1 6 billion km past Uranus in the solar system Jupiter Saturn Uranus and Neptune are called the outer planets Uranus is the second farthest planet from the sun
