Bob Moler's Ephemeris Blog

Ephemeris for Friday, September 24th.*  The sun will rise at 7:31.  It’ll be up for 12 hours and 4 minutes, setting at 7:36.   The moon, 1 day past full, will rise at 7:43 this evening.

Jupiter is the bright star-like object in the east and 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 400 years ago with his small telescope.  Jupiter has 63 satellites in all, 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.

*Times are for the Grand Traverse Area of Northern Michigan, USA.