Wednesday, 12 March 2014

Jupiter - always interesting

I "videoed" Jupiter on the 8 inch Schmidt-cassegrain at the observatory tonight (11th March 2013). I got better results with just the 2x barlow than with 2 2x barlows. I was operating at f/20-22 (focal length just over 4m) and exposures of 1/54 of a second. I captured 2500 frames in 1min40, and stacked the best 1760 of them in Registax 6. The three moons made a beautiful triangle and Callisto cast a rare shadow on to the disk - something I noticed in the eyepiece, plus the red spot was in view. What chance! The Imaging Source (non-cooled) DBK colour camera was pushed into the scope and off I went. The moons to the right were (top to bottom) Europa, Io, Callisto - and you can see it is Callisto causing the shadow. Each moon seemed to have an independent motion to each other as the conjunction developed over the course of an hour or two.

Aurora borealis!

Yeah! I caught a glimpse of the Northern Lights for the first time this solar 'season' on Thurs 27 Mar 22UT. It was not too impressive aesthetically, but lovely to see the lights again. A colourless dim glow was hovering, detached from the horizon and for a time, a shaft of light appeared in the sky just beneath Cassiopeia. The advances in Camera technology (and mine is well out of date) meant an easy capture of the wonderful colours.
Here I've done a stack of 8 x 15s images pointing N, just N of Norwich. I stacked on the ground, not the stars, so they are trailed. The green, lower glow is from atomic Oxygen, i.e. O atoms, emitting during the decay from excited singlet S state to the singlet D state, an allowed transition. The red light, also from atomic O, is only seen at higher altitudes, where the air is much thinner, this would occur at lower altitude but the excited state causing it is knocked back down by collisions with other air molecules. This excited state is the singlet D mentioned above, the 'first' or lowest energy excited state, and it releases its red light with a time constant of about 107 seconds. This means it needs to avoid getting hit for about a minute, in order for it to have a change to spit out its red light. The reason for this slow time is because the transition from singlet D to the 'ground state' (triplet P) is forbidden, as the spin has to change from singlet to triplet, something not allowed by quantum mechanics.