|Date:||26.12.06||Time:||15:33 UT, intervall ~3 s||Exposure:||1/5000s each|
|Field of View:||0.35o||Camera:||Nikon D200||Filter:||none|
|Instrument:||f=1000mm 1/10||Place:||Plettenberg, elevation 1000 m, Germany||Observer:||Till Credner|
Why a blue flash?
A green rim of the setting or rising sun occurs due to differential refraction in the atmosphere. If conditions are extremely clear, also the blue light has a chance to get through, and there might be even a blueish rim.
With a temperature inversion layer in the atmosphere, upper segments of the solar image might get separated from the rest of the solar disc. In the final moments of these elusive segments they do appear green and sometimes even blue (green or blue flash). However, it is not clear to me why in my observations both happens. Most last moments are green, whereas the third frame shows a blue color and at the same time other turbulent segments with a green color (see larger image).
It is the first time I see green and blue flashes simultaneously in one image. I strongly encourage other observers to record video data to show these effects in higher time resolution.