Castle Point Astronomy Club
Mighty Jupiter by Jim Vincent
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Mighty Jupiter by Jim Vincent
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Image taken on 15/10/11 at 22:21 GMT using a Celestron C11, ToUcam pro with a Televue big barlow x2, giving F20. Seeing conditions 7/10.

You can see more of Jim Vincent's photographs on his website by going to our "Links" page.

One could easily be forgiven for thinking that this quite detailed photograph of Jupiter was taken using very sophisticated equipment, housed in a professional observatory sited at some fairly exotic location, such as Hawaii, the Canary Islands or even the Atacama Desert in Chile! (Jim wishes!) A look at the information above however, reveals that this was not the case. It was actually taken using a relatively small amateur telescope and a readily available webcam from nowhere more exotic than Jim's home in southeast Essex. On that basis it very well demonstrates the fact that, these days, amateurs can obtain images of a quality that the professionals would have given their eye teeth for not so very long ago.

Amongst other visible detail, note the small bright object to the right of Jupiter. This is one of its four so-called Galilean moons, specifically Io. A couple of hours prior to taking this photo, Io was just completing a transit of Jupiter’s disc. Transits of the Galilean moons are not particularly easy to observe in small telescopes – the tiny moon gets lost in the glare from Jupiter. However, transits of the moons are often accompanied by a transit of the moon’s shadow, which is much easier to observe as it appears as a tiny black spot on the bright disc of the giant planet.

Jupiter is of course far and away the mightiest of the Sun's family of planets. It's around 320 times the mass of the Earth and is in fact made of enough material to make all the other planets about two and a half times over. This enormous mass means that it is very much the most influential of all the planets in a number of ways. In particular, its huge gravitational pull has a perturbing effect on the orbits of the other planets. That is to say, it is constantly pulling on them, causing their orbits to change slowly over time. Actually Jupiter isn't acting alone in this. Every planet in the Solar System has a slightly perturbing effect on all the others, but Jupiter has by far the largest affect overall. Some idea of the strength of Jupiter's gravity can be had by comparing the magnitude of its effect on the Earth with that of Venus, our closest planetary neighbour. At their respective closest approaches to the Earth, Jupiter is just over fifteen times further from us than Venus. Nevertheless, as a direct result of being about 390 times the mass of Venus, Jupiter exerts nearly 1.7 times as much pull upon the Earth as Venus does.

Over the last forty years we have learnt a huge amount about Jupiter and its environs. This is largely due to various spacecraft that have visited the planet over the years, albeit in most cases rather fleetingly. The process was started in November 1973 when Pioneer 10 started imaging Jupiter from around 25,000,000 kilometres. The process continued through Pioneer 10's closest approach on 4th December 1973 and then, as Pioneer 10 headed off towards the edge of the Solar System on its way into inter-stellar space, it was followed in due course by Pioneer 11 and Voyagers 1 and 2, all of which made similar fly-bys. Although much was learnt from these missions, including the discovery of an extremely faint ring system around the planet, it was the Galileo craft that probably contributed most to our present knowledge of Jupiter, for, unlike its predecessors, Galileo went into orbit around the giant planet and dropped a probe into its atmosphere. The Galileo craft remained in a constantly changing orbit from December 1995 until it was deliberately deorbited on 21st September, 2003 During its time dancing around the Jovian system it visited all four of the Galilean moons and discovered (amongst an array of other things) a number of new much smaller moons, bringing it current total to an amazing 64. Mm - we’ve got one!

With thanks to CPAC member Paul Cooper for his suggestions in the writing of this article.

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