Moons of Jupiter and Great Red Spot

This series of four images was taken on January 28, 2012 during an evening of public observing.  While visitors were observing features on Jupiter with the observatory's main 16" telescope, and using the observatory's other telescopes to study our own Moon, these images were taken using the finderscope riding on the 16" telescope.

The images were taken at 7:28, 7:35, 8:22, and 8:28 pm.  Over the course of this hour, the Galilean moons of Jupiter shifted position.  They all orbit in ellipses around the gas giant planet, but from Earth's point of view in the same plane as the moons' orbits, they appear to move in a line toward and away from Jupiter.

The innermost moon, volcanic Io, is hidden behind Jupiter.  On the right, enormous Ganymede approaches Jupiter.  Ganymede is the largest moon in the Solar System, larger though less massive than the planet Mercury.  Just to the left of Jupiter, the icy waterworld Europa approaches Jupiter and then crosses in front of Jupiter's disk, vanishing from our view against Jupiter's glare.  (The finderscope is not a large enough telescope to permit us to see Europa against Jupiter's brightness.)  On the far left, the large moon Callisto is slowly approaching Jupiter from its point of greatest elongation: its largest angle from Earth's point of view.

By watching the progress of these four largest moons of Jupiter over several nights in the winter of 1609, Galileo deduced that these "stars" must actually be orbiting the planet.  This posed a serious challenge to the dominant theory at the time that everything in the Universe orbited the Earth.

The images also show stripes across Jupiter's surface: the tops of the gas giant's dramatic cloud bands.  In the top three images, the giant hurricane called the Great Red Spot is distinguishable as a paler interruption in the thick southern cloud band, rotating toward the right in the later images.

Telescope: Finderscope attached to 16" Boller & Chivens.

Camera: SKYnyx 2-2M.