Io, Europa, Ganymede, and Callisto are all brighter than 6th magnitude and easy detections in most any binocular. (Often, one or more will be passing in front of or behind Jupiter's disc.) In fact, each moon would readily be visible from a dark sky without
any magnification if not for the tremendous glare of the gas giant.
Every so often a brighter field star or two will attempt to sneak into the Galilean plane, but Jove soon gets annoyed and kicks these occasional stellar imposters out of the litter.
During the last days of June 2008 this '5th moon'
is played by a 5.6 mag background star in Sagittarius. Also known as HR 7327, the class A5/FK blue-white sun resides at a distance of just over 191 lightyears.
So while we're admiring our neighbor Jupiter during this close conjunction, it may be interesting to note that; Charles Messier was 85 years old, the bicycle was invented, and Mississippi was admitted to the union as the 20th state when that light from distant HR 7327 began its journey toward us.
Enjoy the show.
Other Jovian/stellar conjunctions through 2008:
Jul11 7.9mag sao187846 (occultation)
Jul29 6.9mag h129 (double; 8.4mag at 8")
Aug19 5.9mag sao187468 + 7.6mag sao187480
Sep21 same as above (direct motion)
Oct17 6.9mag h129 (double; 8.4mag at 8")
Dec02 8.0mag sao188346 + 7.9mag sao188355
Dec13 7.5mag bu467 + 8.0mag sao188551
Saber Does The Stars at
www.astronomyblogs.com/member/saberscorpx
