Sunday, October 28, 2018

Queen of the Gods!

Our best image of Juno, showing its highly irregular shape. 
Juno is 145 miles across at its widest.

Exactly 2 weeks from today will be your best chance to observe the third asteroid to be discovered (although by far not the 3rd largest) - Juno, named for the mythical wife of Jupiter.

Bottom line on top: This will be Juno's most favorable opposition since 2005, and will not be this close to the Earth again until 2031 (by which date I will either be 79 years old, or dead). This is due to Juno's highly eccentric orbit, worse than Mars, which makes for some oppositions being far more favorable than others. (See illustration below.)

Although assigned the number 3 due to its order of discovery, Juno is actually only the 11th largest asteroid (exceeded by Ceres, Vesta, Pallas, Hygeia, Interamnia, Europa, Davida, Sylvia, Cybele, and Eunomia). Where it does excel, however, is in its high surface reflectivity, which with an apparent magnitude of 7.5 makes Juno (at opposition) brighter than Neptune. No wonder it was one of the first asteroids to be discovered! Juno was even listed amongst the planets for 38 years before being demoted from that lofty status to mere asteroid in 1845.

Although opposition does not occur until the 17th of November, the 11th will be your best chance of actually seeing Juno, due to its near miss of naked eye star 32 Eridani (magnitude 4.46) on that night. Try to spot it on the 10th (weather permitting, of course), and take a second look on the 11th. See which star in 32 Eridani's vicinity has moved since the night before - that's Juno! And if conditions permit, go for the 12th as well. After that, Juno will increasingly blend in with the anonymous mass of similarly looking points of light which are, of course, the background stars.

Useful hint: Sketch the stars near to 32 Eridani each night as accurately as you can. That will aid you immeasurably in positively identifying Juno, since it will be the only "dot" that moves night to night.

Juno will be bright enough to observe this opposition uning only binoculars - no telescope required. In fact, that is my intention - to spot Juno using only my 8X56 binos. If that does not work, then and only then will I resort to a telescopic search.

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