Uranus (named after a primal Greek god of the sky, the son and husband of Gaia, and father of the Titans) was discovered on this day in 1781 by William Herschel. It’s the 7th furthest planet from the Sun, orbiting at approximately 2.8 billion km, and is often classed as an ice giant with Neptune, as well as being a gas giant. Uranus is the third largest planet by radius (about 25,000km, or 4 Earths), but only the fourth largest by mass (roughly 14 times as massive as Earth).
As with the other giant planets, Uranus has a plentiful supply of moons (27 at the last count). The largest five are Oberon, Titania, Umbriel, Miranda and Ariel. None of the Uranian moons are particularly large, with the biggest, Titania, being less than half the size of our Moon. The naming convention for Uranian moons is that they are all characters from either the plays of Shakespeare or The Rape of the Lock by Alexander Pope. Most of the Shakespearean names were taken from The Tempest and A Midsummer Night’s Dream, but I suppose they started running out after a while, so nowadays anything goes.
Uranus also has a ring system. The rings, of which 13 are known, are dark, narrow, and probably quite young (less than 600 million years old). They are thought to be the remnants of one or more shattered moons. The rings can be clustered together in three groups: nine main rings, two dusty ones, and two outer rings, including the brightest, the ε (epsilon) ring.
The atmosphere of Uranus (by which I mean the outer layers) usually presents a blank face to watching humans, and the Voyager photographs painted a picture of a serene world. But recently (August 2014) a collection of enormous bright spots have been observed, showing that giant storms can sometimes flare up on the planet.
1980 – CALYPSO, one of the smaller of Saturn’s fifty-three named moons, was discovered on this day in 1980. It’s an irregularly-shaped Trojan, trailing 60 degrees behind the larger moon Tethys at the L5 Lagrangian point, something I’m still planning on writing a blog about (another Trojan, Telesto, occupies a position 60 degrees ahead of Tethys, called the L4). Calypso is named after a daughter of the Titans Oceanus and Tethys.
1969 – APOLLO 9, under the command of James McDivitt, splashed down in the North Atlantic on March 13th 1969, after just over 10 days in orbit.
1855 – Birth of Percival Lowell, proponent of Martian canals, and founder of the Lowell Observatory, one of the oldest in the United States.