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

The correct answer is B. Pluto was formally downgraded from planet to dwarf planet after a vote by the International Astronomical Union.

Explanation:

Pluto was discovered on February 18, 1930 by American astronomer Clyde William Tombaugh from the Lowell Observatory in Flagstaff, Arizona, and was considered the ninth and smallest planet in the solar system by the International Astronomical Union and public opinion since then until 2006, although its membership in the group of planets in the solar system was always the subject of controversy among astronomers.

After an intense debate, and with the proposal of Uruguayan astronomers Julio Angel Fernandez and Gonzalo Tancredi before the General Assembly of the International Astronomical Union in Prague, Czech Republic, it was unanimously decided to reclassify Pluto as a dwarf planet, requiring that a planet must have orbital dominance. Since September 7, 2006, it has the number 134340, granted by the Center for Minor Planets.

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