When was Pluto formally downgraded from planet to dwarf planet? A. After The New York Times published an article about Pluto B.
After a vote by the International Astronomical Union C. After Dr. Tyson received a letter from a concerned child D. After the Hayden Planetarium's solar system exhibit opened
B. After a vote by the International Astronomical Union.
Explanation:
Pluto was downgraded following a meeting of the International Astronomical Union (IAU) in August 2006. The Union revised what astronomy defined as "planet," and settled on three essential characteristics that a celestial body needs to have in order to be considered a planet: the object should be in orbit around the Sun, it should have sufficient mass to assume a nearly round shape and it should have cleared the neighbourhood around its orbit. Following a vote, it was established that Pluto did not fulfill the necessary requirements to be considered a planet.
