Elara, a moon of Jupiter
7,252,382 miles
50 miles
Elara is a moon of Jupiter. It was discovered in 1905 and takes about 260 days to complete a journey around the planet, orbiting at a distance of approximately 11.5 million kilometres (7 million miles). It has a diameter of only 80 kilometres (50 miles) but is Jupiter's eighth largest moon.
Elara is an irregular prograde moon. This means that it was captured by Jupiter's pull of gravity and orbits in the same direction as Jupiter's rotation. As with many irregular moons, Elara has an inclined (tilted) and eccentric (not circular) orbit. It orbits at an angle of 25 degrees with an eccentricity of 0.217.
Elara is part of the Himalia group of Jupiter's moons. The other moons in this group are Leda, Himalia, Ersa, Pandia, Lysithea and Dia. These moons share similar orbital characteristics and may have the same origin. Himalia is the largest of these moons and gives the group its name. Elara is the second largest in the group. It is thought that Himalia may once have been an asteroid which orbited in the asteroid belt. A possible collision nudged it out of the asteroid belt and towards Jupiter. The collision also caused parts of it to break off to become the smaller moons in the group, with Elara being one of those moons.
Elara was discovered by the American astronomer Charles Dillon Perrine (1867 - 1951) on 21st February 1905 at the Lick Observatory in sunny California. It was the seventh moon of Jupiter to be found. Perrine also discovered nearby Himalia in the previous year.
Although it was discovered in 1905, Elara didn't get its name until 1975. Before this, it was usually referred to as Jupiter VII as it was the seventh moon to be discovered in orbit of Jupiter. For a time between 1955 and 1975, it was sometimes called Hera. In Greek mythology, Hera was Zeus' (Jupiter's) sister and also his wife.
Elara is a figure from Greek mythology. She was a princess, the daughter of King Orchomenus. Zeus fell in love with Elara, as he seemed to do with a lot of people, but to keep her a secret from his wife Hera, he hid Elara deep below the Earth's surface. While there, Elara gave birth to their child Tityos who was a giant. Elara died in childbirth, and Tityos later emerged on Earth's surface via a cave in what is now the Greek island of Euboea. As an adult, Tityos attempted to attack the goddess Leto, so Zeus threw a thunderbolt at him and sent him to Tartarus, an underworld place of torment where he would be stretched while two vultures fed on his liver each night.
There is a rule that all irregular prograde moons of Jupiter must end with the letter 'a', and Elara is an example of a moon following this rule. Well done Elara.
