Pluto

7/11 — 數學計算顯示，這一天是矮行星冥王星最後一次在1979年之前進入海王星軌道的日子。

2/18 — 在研究一月份攝攝的照片時，克莱德·托姆博发现冥王星。

3/13 — The news of the discovery of Pluto is telegraphed to the Harvard College Observatory.

5/1 — 矮行星冥王星正式命名。

2/7 — 海王星自發現以來，冥王星首次進入海王星軌道。

4/25 — Pioneer 10 travels beyond Pluto's orbit.

2/11 — Pluto crosses Neptune's orbit, ending a nearly 20-year period (since 1979) when it was closer to the Sun than the gas giant; Pluto is not expected to interact with Neptune's orbit for another 228 years.

5/18 — 哈伯太空望遠鏡第二張照片確認冥王星有兩顆額外衛星，Nix和Hydra。

6/21 — 冥王星新發現的衛星正式命名為尼克斯和海德拉。

8/24 — The International Astronomical Union (IAU) redefines the term "planet" such that Pluto is now considered a dwarf planet.

7/14 — NASA之新地平線探測器進行對冥王星的首次飛越，從而完成對太陽系的首個調查。

2/4 — 美國天文學家和學者克莱德·汤博（Clyde Tombaugh，1997年去世）發現了冥王星。

7/11 — Venetia Burney, English educator, who named Pluto (d. 2009)

1/17 — Clyde Tombaugh, American astronomer and academic, discovered Pluto (b. 1906)