Timeline: the Story of the Planets
Science correspondent Alok Jha observes the rise and fall of Pluto.
The word planet comes from the ancient Greek for "wanderer" because early astronomers would see them moving in the sky against a stationary backdrop of stars.
Ancient Greeks and Romans recognized five planets, each circling the Earth according to laws laid out by Ptolemy in 2AD. These were Mercury, Venus, Mars, Jupiter and Saturn.
1612 - Galileo Galilei spots Neptune; at first he mistakes it for a fixed star.
1781 - William Herschel discovers Uranus, the first planet to be found using a telescope.
1930 - Pluto was observed by Clyde Tombaugh at the Lowell Observatory in Arizona and immediately named the ninth planet.
1992 - First large object found in the Kuiper Belt, a mass of comets and rocks that sits on the outer edge of the solar system.
2003 - A Kuiper belt object called 2003 UB313 (later re-named Eris) seen by astronomers and measured to be of a similar size to Pluto, re-igniting debate over whether Pluto should be defined as a planet.
2006 - International Astronomical Union clarifies the definition of a planet to ensure two conditions are met: a planet must orbit a star without being a star itself, and it has to be big enough for its gravity to pull it into a spherical shape. Pluto and Eris are put in the category of dwarf planets.
Ancient Greeks and Romans recognized five planets, each circling the Earth according to laws laid out by Ptolemy in 2AD. These were Mercury, Venus, Mars, Jupiter and Saturn.
1612 - Galileo Galilei spots Neptune; at first he mistakes it for a fixed star.
1781 - William Herschel discovers Uranus, the first planet to be found using a telescope.
1930 - Pluto was observed by Clyde Tombaugh at the Lowell Observatory in Arizona and immediately named the ninth planet.
1992 - First large object found in the Kuiper Belt, a mass of comets and rocks that sits on the outer edge of the solar system.
2003 - A Kuiper belt object called 2003 UB313 (later re-named Eris) seen by astronomers and measured to be of a similar size to Pluto, re-igniting debate over whether Pluto should be defined as a planet.
2006 - International Astronomical Union clarifies the definition of a planet to ensure two conditions are met: a planet must orbit a star without being a star itself, and it has to be big enough for its gravity to pull it into a spherical shape. Pluto and Eris are put in the category of dwarf planets.
Use the feedback form below to submit your comments.
Use the form below to email this article to your friends.
- Facts about Venus
- Planet Jupiter
- Pluto the Planet: Facts about the Planet Pluto
- Mercury Planet: Facts on the Planet Mercury
- Moon Facts
- Venus - Beauty & the Beast
- The Planet Venus
- Puzzling Pluto
- Marvellous Moon
- Space Mission to Photograph Apollo Landing Sites
- Space Probe Paves Way for European Moon Landing
- Largest Telescope Starts Gazing
- Pluto Loses 'battle of the Planets'
- One Giant Blip for Mankind As Moon Landing Tapes Are Mislaid
- European Mission to Venus Blasts Off
- Spaniards Go Goggle-eyed for Rare Solar Eclipse
- China and Japan Launch Race to the Moon
- Probe Lands on Saturn Moon
- US-European Mission Explores Saturn's Moon Mysteries
- Astronomers Say Farewell to Planet Pluto