Jupiter and Io  (September 2009)

A Dangerous Observation Jupiter is big and fast.  Our solar system's largest planet, its diameter is over 10 times that of Earth, yet it rotates almost 2.5 times faster, so Jovian days are only about 10 hours long.    Jupiter's four largest moons are visible through any telescope (Fig. 1).  They were discovered by Galileo in January 1610, almost exactly 400 years ago, and are known as the Galilean moons in honor of their discoverer.  Io, the closest Galilean moon to Jupiter's surface, takes less than 2 Earth days to complete one orbit around Jupiter compared to the month it takes for Earth's moon to complete an orbit.  Because of their rapid orbital motion, the Galilean moons have clearly different positions when they are observed through a telescope on successive nights (Fig. 2).  This led Galileo to conclude that the moons were actually orbiting around Jupiter, a conclusion that was important evidence that Earth is not at the center of the universe.  After discovering the moons of Jupiter, Galileo began publicly supporting the idea that the Sun, not Earth, was at the center of the universe.  This idea was against Catholic church doctrine at the time, and after several warnings, Galileo was placed under house arrest during the last 10 years of his life.    Listed below are the technical details of how we obtained our image of Jupiter. Telescope:  Celestron C9.25 (235 mm aperture, 2350 mm focal length) Telescope mount:  Losmandy GM-8 equatorial mount with digital clock drive Camera:  Canon EOS 5D Mark II digital SLR Camera coupling:  Positive projection with 15 mm Meade Super Plössl eyepiece inside Meade tele-extender yielding an additional 4X magnification Data acquisition:  High-definition (1920 x 1080 pixels) movie captured at 30 frames/second Image processing:  Exported approximately 900 frames from captured movie with Apple QuickTime Player. Cropped all frames with GraphicConverter. Aligned frames with Registax 5 program. Summed approximately 250 frames with the highest quality according to Registax. Adjusted brightness and contrast in Adobe Photoshop. ( back to home page)

Fig. 1.  Jupiter and its moon Io observed through a telescope from the driveway of our house in Cockeysville, Maryland on 2009 Sep 19 21:45 EDT (2009 Sep 20 01:45 UT).  Io casts a shadow on Jupiter's surface.  Jupiter's Great Red Spot is visible at approximately the 11 o'clock position.  When viewed on a typical computer monitor, the apparent magnification of this image is about 400X. Fig. 2.  A page from the first edition of Galileo's Sidereus Nuncius (Starry Messenger, in English), a treatise published in March 1610 that describes observations he made with his telescope.  This page shows some of Galileo's observations of Jupiter's moons, with a circle indicating Jupiter's position and asterisks indicating positions of the moons on different nights.  (Source: Linda Hall Library)

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