May 29, 2020

AstroEvent: A 2xJovian Moon Transit.

One of the first things that Galileo noticed with his primitive telescope was the moons of Jupiter. This ‘solar system in miniature’ fascinated him, as he watched and recorded the changes in position presented by these four moons night to night. Even today, watching these changes can be a fun endeavor, and is a view available to even the smallest telescopes. This week, I challenge you to try and view a double transit of the Galilean moons.

The shadows of each moon present a differing character of their own; harder still to spot are the actual bodies of these worlds as they pass in front of the Jovian cloud tops. Io, the closest moon to Jupiter, presents a large, diffuse shadow, while Callisto, the most distant, displays a shadow that is and intense, tiny dot. Io is also the most frequent transit-er, while the outer moons may miss the disk entirely due to the orientation and inclination of their orbits. Jupiter passed quadrature last month on December 18th, which means that it and its moons are casting shadows well off to the east. On the night of Monday, January 24th, you can catch Io, Ganymede, and the shadow of Io all in a nice portrait as simulated above. The Great Red Spot might just be visible, along with an anemic but returning Southern Equatorial Belt. This is the last chance to catch a double moon transit prior to Jupiter’s conjunction with the Sun on April 7th, 2011.

The astro-word for this week is Medician Stars. When Galileo wasn’t busy torque-ing off church officials, he, like many scientists before & since, was busy attempting to secure funding. Galileo first proposed that the new found moons be named the ‘Medician Stars’ in honor of the infamous Medici clan that then ruled Florence and Tuscany. This was even formalized in the first printing of Galileo’s landmark work, Sidereus Nuncius (The Starry Messenger) but thankfully, fell to the wayside along with other astronomical financial appeals such as George’s Planet which later became Uranus, also currently lurking in the general area of Jupiter tonite!

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