This photo of Jupiter was taken on 15-August-2009. To the right of the planet can be seen two of Jupiter's moons, Ganymede (closest to the planet) and Io.
Ganymede and Io, along with two other moons of Jupiter, Callisto and Europa, are known as the "Galilean moons" because they were first observed by the Italian astronomer and philosopher Galileo Galilei in December, 1609 or January, 1610. Galileo observed these moons with a three inch refractor, and after studying them for several nights he concluded that they were indeed satellites of Jupiter rather than stars, which he first believed, and that they were orbiting Jupiter. These observations were in contradiction to the widely held belief of the time that the Earth was the center of the universe and that all celestial bodies orbited the Earth. While Galileo's observations, subsequently confirmed by other observers, dealt a severe blow to the Earth-centered universe theory, Galileo himself believed the Copernican theory that the Sun was the center of the universe, although his new observations proved that other celestial bodies could have their own satellites. The Catholic Church, however, held on to the belief that the Earth was the center of the universe, and Galileo's steadfast refusal to endorse this doctrine eventually resulted in his conviction for heresy. He was sentenced to house arrest for the remainder of his life.
Callisto is outside of the frame of this image on the right side, and Europa is outside of the frame of the image on the left side. The four Galilean Moons are easily seen with almost any telescope, and can even be observed with good binoculars. They can be seen to pass behind and in front of the planet in their orbits, and their positions relative to each other change by the hour, as they all orbit Jupiter at different distances and speeds.
Jupiter is said to be at opposition when the Earth is directly between Jupiter and the sun, and this event occurs about every 400 days. This year (2009) the opposition was on August 14, one day before I took this photo. Opposition represents the closest approach of the outer planets to Earth in a given orbital cycle, and is generally a good time to observe the planets. When opposition occurs close to the winter solstice in late December, viewing is even better from Earth's northern hemisphere as the planet's altitude above our horizon is at it's highest point, resulting in less interference with the view due to our atmosphere. Jupiter's altitude at opposition will continue to increase each year until 2014, after which it will slowly decrease again.
This photo was produced by combining about 150 frames of video out of a sequence of 1200 frames acquired over two minutes (10 frames per second) with a Philips SPC-900NC webcam attached to the prime focus of my 8" newtonian reflector telescope. The "seeing", or effect of atmospheric turbulence, was below average on this night, resulting in a somewhat fuzzy image. Two minutes is about the maximum length for a video sequence of Jupiter if the goal is to produce a composite still image, because Jupiter rotates quite rapidly, completing a revolution in a little under 10 hours. Longer sequences result in blurry composite images as the surface features of the planet move significantly from the start to the end of the sequence.
The next image in this gallery is an animation showing a short sequence of frames from one of the videos captured on this night.
If I can acquire images on a better night in the near future I will replace this image with a sharper one.
