Archive for May 21, 2018

05/21/2018 – Ephemeris – 408 years ago Galileo discovered that Jupiter had moons

May 21, 2018 Comments off

Ephemeris for Monday, May 21st. Today the Sun will be up for 15 hours and 2 minutes, setting at 9:10, and it will rise tomorrow at 6:07. The Moon, at first quarter today, will set at 2:55 tomorrow morning.

Jupiter is the bright star-like object in the southeast in the evening. In telescopes and even in binoculars the observer can spot up to four stars nearby. These aren’t stars, but moons or satellites of Jupiter. Galileo discovered them 408 years ago with his small telescope. Jupiter has 69 satellites in all at last count, but the rest are tiny objects. Of the four ‘Galilean’ satellites all but one is larger than the Moon. They are, in order from Jupiter Io, a volcano riddled world which is constantly resurfacing itself. Next is Europa an icy moon with a good probability of a salty ocean beneath. Giant Ganymede is next, larger than Mercury, it is also icy with the possibility of an ocean. Last is Callisto a dark moon with bright craters.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Galileo's moons

Multiple night sightings of Jupiter’s moons by Galileo.

Jupiter and its moons tonight

Jupiter and its moons tonight, May 21, 2018. Created using Cartes du Ciel (Sky Charts).