Curated playlist
Astronomical objects known since antiquity
- Mercury (planet)Mercury's day, from one sunrise to the next, lasts about 176 Earth days. That is twice as long as its year.
- JupiterIn July 1994, Comet Shoemaker-Levy 9 crashed into Jupiter while observatories watched.
- SaturnSaturn is the only planet in the Solar System that would float in water. It is still more than 95 times Earth's mass.
- MarsMars has a volcano about three times as tall as Mount Everest. Olympus Mons climbs nearly 26 kilometers from the plains.
- ProcyonThe star Procyon has a hidden companion that astronomers predicted in 1844 and first saw in 1896.
- VenusOn Venus, a single day lasts longer than its entire year. The planet also spins backward, so the Sun rises in the west.
- SunA photon born in the Sun's core can take 10,000 to 170,000 years to reach the surface.
- EarthA Mars-sized object called Theia hit the young Earth, and the scattered debris became the Moon.
- MoonThe Moon is drifting away from Earth by 38 millimeters every year. That is about the rate human fingernails grow.
- Milky WayUntil the early 1920s, most astronomers thought the Milky Way held every star in the universe.
- Alpha CentauriAlpha Centauri looks like one bright star but is really three. The faintest was not found until 1915.
- Halley's CometHalley's Comet turned out to be nearly as black as coal. Spacecraft in 1986 found it reflects only 4% of sunlight.