Curated category
Astronomical objects known since antiquity
- Mercury (planet)Mercury is the first planet from the Sun and the smallest in the Solar System, with an equatorial radius of 2439.7 km. It is so close to the Sun that it…
- JupiterJupiter is the fifth planet from the Sun and the largest in the Solar System. Its mass is nearly 2.5 times that of all the other planets combined.
- SaturnSaturn is the only planet in the Solar System that would float in water. Its average density is about 30 percent less than water, giving it a specific…
- MarsMars is the fourth planet from the Sun, a desert-like rocky world that glows orange-red in the night sky. The ancient Sumerians called it Nergal, the god of…
- SunThe Sun fuses about 600 billion kilograms of hydrogen into helium every second. In that same second, 4 billion kilograms of matter vanish, converted entirely…
- EarthEarth is the third planet from the Sun, and the only place in the known universe where life has ever taken hold. At 4.5 billion years old, it formed from gas…
- MoonThe Moon is the only natural satellite of Earth, and it orbits at an average distance of 384,399 km. That gap is roughly thirty times the width of Earth.
- Milky WayThe Milky Way is the galaxy that includes the Solar System, and its name comes from how it looks from Earth: a hazy band of light arching across the night…
- Alpha CentauriAlpha Centauri is not one star but three, and the closest of them sits just 4.2465 light-years from the Sun. That makes it our nearest stellar neighbor by a…
- Halley's CometHalley's Comet is the only known short-period comet that returns to Earth's skies reliably enough to be seen with the naked eye, once in a human lifetime.