This coming weekend is the best time to catch the annual Perseids meteor showers, named for the constellation Perseus. The Perseus constellation is named for the man who beheaded Medusa. In early star atlases, the constellation is drawn as a sword-wielding Perseus holding Medusa’s head, represented by the bright star Algol, derived from the Arabic word meaning, “The Demon’s Head.”
Before dawn, look to the east to find Jupiter rising — the largest planet in our solar system. Jupiter and the orbiting Galilean moons are visible with binoculars.
Jupiter itself is believed to be the oldest planet in our solar system, and the largest. The sheer size of Jupiter dictates the very shape of our solar system. After the Moon and Venus, Jupiter shines the brightest in the night sky. The Greeks called this planet Zeus, and the Romans called him Jupiter, King of the Roman Gods. Jupiter was the god of thunder, lightning, and storms — he cloaked himself in thick clouds to hide from his wife Juno when she discovered his affairs. Like the mythological king, Jupiter the planet is one giant gas ball.
The four largest moons of Jupiter — Ganymede, Callisto, Io, and Europa — can be seen from Earth with binoculars. The four moons collectively are referred to as the Galilean Moons, after Galileo Galilea, who documented their existence in 1610. Simon Marius, a contemporary of Galileo, named the four moons after Jupiter’s lovers … the ones Jupiter tried to hide from Juno, but she could see right through his cloak. NASA launched spacecraft Juno in 2011 to do just that. In recent years, Juno has returned stunning images of Io and Europa, in addition to Jupiter.
Ganymede is the largest moon in our solar system, even larger than Mercury. It is made of water-ice, and may hold a salt water ocean under the surface. This moon was named after Ganymede, the son of the King of Troy. In the Iliad, Homer describes Ganymede as, “the loveliest born of the race of mortals, and therefore the gods caught him away to themselves, to be Zeus’ wine-pourer.”
Callisto, Jupiter’s second-largest moon, orbits farthest from the planet and is considered a dead moon with a lack of any discernable geologic activity. The colorful surface is heavily pock-marked with impact craters. In Greek mythology, Callisto was a nymph that Zeus tricked into a tryst. When Zeus’s wife Hera found out, she turned Callisto into a bear.
Io is equal in size to Earth’s Moon. Io is the most geologically active body in the solar system, with hundreds of active volcanoes. In Greek mythology, Zeus turned himself into a cloud and engulfed Io without her consent. He then turned her into a white cow. No wonder Io is the most volatile moon in our solar system.
Europa is the smallest of the Galilean Moons. The smooth surface is composed of rock and ice and shows an environment suitable for life. Europa, the Greek, was a great-great-granddaughter of Io. Zeus, aka Jupiter, finds her to be irresistible and transforms himself into a white bull to attract her attention. Europa has an affinity for bovines, perhaps because her great-great-grandmother was cursed. In short order, Europa gives birth to the Minotaur, a half-man, half-bull that moves into King Minos’s labyrinth on Crete.
On Wednesday, Aug. 9, our own Moon formed a predawn conjunction with Jupiter. If, perchance, you sighted a cow jumping over the moon, you could say hello to Io.