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The planets (and the Sun)


From the Greek word for "wandering star". Bright enough to be seen naked eye, large enough and close enough to be imaged with a humble webcam attached to a scope.

The webcam succeeds by capturing several hundreds, if not thousands of frames, in an avi. movie file. These individual frames can then be analysed for clarity and focus. This technique of then using the best individual images can avoid the biggest factor that affects planetary observation - the fact that the atmosphere is not static but wobbles and affects the image you see by diffracting the light in constantly changing ways. Try watching a bright light over the top of a hot chimney - then imagine the same effect vastly magnified. The best indiviual frames are then stacked on top of each other and averaged to increase signal and reduce random noise.

The alternative us to build a telescope with active optics that change shape to allow for the changing atmospheric distortion. This is basically done by building a mirror made of many individual segments that can move independently, and are controlled by computer which also monitors a benchmark star, and by analyising the changes in shape of said benchmark star, alters the mirror configuration to adapt to the current effect of the atmosphere - hence the term adaptive optics. The changes are made thousands of times a second and involve fractions of a millimetre in movement. So not cheap or easy, and certainly makes a 55 webcam look very good value for money, madam!

The best amateurs I have seen are using extremely fast webcams that can capture many frames a second without compressing the data, and are shooting from large aperture big focal length Newtonians, usually in Dobsonian/ alt.az form. The large aperture allows good light grasp to keep shutter speeds down, and also allows better definition (which is a function of aperture diameter). Likewise the long focal length gives good magnification. However they are not the sort of tackle you can slip in the boot of your Mini for a trip out. It's a bit more like owning a chimney stack.....

Anyway, here's some of mine......


Note the equatorial banding, the great red spot, and three of its moons having a bit of a day out as well - two appear as small white dots either side of Jupiter but the third is in front of Jupiter itself at about 1 o'clock. If you're really swanky, you can also capture the shadow of the moons on Jupiter's surface.


You'll see that the rings are not all the same and have gaps in between. The biggest is the Cassini division




The same angular size as a grapefruit seen from a mile away. A tricky one to get as it is so small, and the details on it are so fine.



The Sun

It is usually at this point on any other website you will be recommended not to look at the sun through any optical device unless blah blah blah blindness blah blah balh Galileo himself blah blah blah back your head will burn off blah blah blah. I'd guess that if you're capable of using a computer, you've worked this out for yourself. Having said that, the most common accident when solar observing is to forget to cap the finder scope, then let it set fire to your hair/hat as you gaze away. There are two safe ways - a solar filter over the objective, or projection onto a piece of white card. Anyway looking at the sun is fun, and there are three things to look for - sunspots, flares and transits. Sunspots are relatively cool areas that appear black; flares are still unfashionable; transits are the passages of the inner planets across the sun's disc. A transit of the moon across the sun is however called an eclipse. All ist klar?



Taken with a Nikon 995, and a Baader solar film filter. The filter produces a white light image, slightly tinged with violet. If you reall want to, you can then apply false colour (here orange) to make it look like the real sun in pictures that you drew at school.



The transit of Venus

8 June 2004, and tough luck if you missed it as the next one visible in the UK is in about 111 years time I think. Thanks to my proof reader ELR!


First sighting as the cloud parted. The transit was already in progress.

then the exit phase. Large amounts of haze I am afraid but never mind!



And closer....

then gone. Bye bye!



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