Bob Moler's Ephemeris Blog

Wednesday, January 11th.  The sun will rise at 8:17.  It’ll be up for 9 hours and 5 minutes, setting at 5:22.   The moon, 2 days past full, will rise at 8:29 this evening.

It’s time again to take a look at the whereabouts of the bright planets.  Venus is brilliant in the southwestern sky after sunset and will set at 8:25.  Jupiter is the most prominent planet of the evening sky, once Venus sets.  It’s located high in the south and is seen against the stars of the constellation Aries.  It will pass due south at 7:15 p.m.  It will set at 2:00 a.m.. Jupiter is a great sight in a small telescope with its four moons which change position from night to night. Mars will rise at 10:27 p.m in the east northeast and is below the hind end of the  constellation Leo the lion.  It is 88 million miles away and closing.  Mars will pass due south at 4:54 a.m.  Saturn will rise at 1:41 a.m. just to the left of the bright star Spica in the east southeast.

* Times, as always are for the Traverse City/Interlochen area of  Michigan.

Addendum

Overexposed Jupiter and its moons. My archival image.

The four Galilean satellites or moons of Jupiter are in order of distance from Jupiter Io, Europa, Ganymede and Callisto.  They all orbit near Jupiter’s equator, and Jupiter itself has a very small axial tilt of about 3 degrees so the satellites seem to shuffle from one side to the other of Jupiter.  The pattern is different night.

The programs Stellarium, Cartes du Ciel, and other sources including http://www.calsky.com can be used to determine the positions of the satellites.  But there are clues by just looking at them.

• Io is closest to Jupiter and generally appears so.  In the photograph above it appears as a bump on the left edge of Jupiter.  It has a slight reddish tinge.
• Europa is dimmer than Io and also is usually close to Jupiter.
• Ganymede is easy.  It’s the brightest.
• Callisto is usually found the farthest from Jupiter and is also the dimmest of the four.

Based on the photograph alone, which is undated, I’d guess that from left to right we have Callisto and Io to the left of Jupiter, Europa and Ganymede to the right.

Sometimes fewer than four satellites can be seen.  They can hide in front of Jupiter, usually casting their shadow on the planet, behind Jupiter or in its shadow.  Calsky will give you the times for your location.

Update

I located the date of the above image.  It was taken the evening of March 17, 1989.  A check with Cartes du Ciel (Sky Charts) confirm the satellite’s locations and order.  Io was just ending a transit (passing in front ) of Jupiter.