In which year did the International Astronomical Union reclassify Pluto as a dwarf planet?
- A.1996
- B.2003
- C.2006
- D.2011
Correct answer
Explanation
The correct answer is C, 2006. In that year the International Astronomical Union adopted a formal definition of a planet: a body that orbits the Sun, is massive enough for its own gravity to pull it into a nearly round shape, and has cleared the neighbourhood around its orbit. Pluto, discovered in 1930, satisfies the first two conditions but shares its region with many other bodies of the Kuiper belt, so it was moved to the new class of dwarf planets.
Options A, B and D name years in which no such decision was taken. Since 2006 the solar system has been described as having eight planets, and questions that ask for the number of planets expect the answer eight. Remember also that Ceres, the largest body of the asteroid belt, is counted among the dwarf planets under the same definition.
Read the full article: Solar System and the Earth: Planets, Moon and Motions
Practice Questions
View allWhich is the hottest planet of the solar system?
- A.Mercury
- B.Venus
- C.Mars
- D.Jupiter
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Venus is wrapped in a very thick atmosphere of carbon dioxide, which lets sunlight in but does not let the heat escape.
Read the full explanation →Approximately how long does sunlight take to reach the Earth?
- A.8 minutes 20 seconds
- B.1.3 seconds
- C.4.2 years
- D.24 hours
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The Sun is about 149.6 million kilometres from the Earth, a distance called one astronomical unit, and light travels about three lakh kilometres in a second.
Read the full explanation →Which is the largest planet of the solar system?
- A.Saturn
- B.Neptune
- C.Jupiter
- D.Uranus
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Jupiter is the fifth planet from the Sun and the largest of all by both diameter and mass; it is a gas giant of hydrogen and helium.
Read the full explanation →Apart from Uranus, which planet rotates on its axis from east to west, that is in a direction opposite to most planets?
- A.Mercury
- B.Venus
- C.Mars
- D.Saturn
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Almost every planet, the Earth included, rotates from west to east, which is why the Sun appears to rise in the east.
Read the full explanation →The occurrence of seasons on the Earth is caused mainly by which of the following?
- A.The changing distance between the Earth and the Sun
- B.The rotation of the Earth on its axis
- C.The tilt of the Earth's axis along with its revolution around the Sun
- D.The gravitational pull of the Moon
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The axis of the Earth is tilted about 23.5 degrees from the vertical and keeps pointing in the same direction throughout the year.
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