[Placidus (Mike and Trish)]

Here is the Crab Nebula, taken under dodgy conditions, and nowhere near enough exposure.

We've been off-air due to technical problems with the dome roof opener. The H-bridge limit switch input (an innocent looking 8015 quad AND gate) was possibly fried after a vicious thunderstorm - we've had some impressive jump-out-of-your-skin thunder. Replaced the chip and we're now operational but yet to see how robust everything is, or whether there is other damage.

Apart from Bildan, everyone else on IIS is wisely leaving the far north alone, perhaps because the seeing has been so appalling. Last night we had and FWHM of 10 pixels, and we lost two subs to intermittent cloud, but we've been waiting for ages and ages, so here's half a crab.

Six hrs of H-alpha mapped to R+G, and only 3hrs of OIII mapped to blue, then palette rotated -15 degrees to give a quarter nod to natural colour. (To recover individual channels, rotate palette +15.)

What can we see that nobody else has mentioned? There is a small and very faint slightly streaky tongue of light (about 90 pixels = 50 sec arc high) heading off toward 9 o'clock, almost to the left hand edge of field, seen in both H-alpha and OIII, that isn't obvious in say the Hubble image or any other that we're aware of.

Question: We've read that the blue glow of the Crab is Cerenkov radiation - electrons spiralling in a powerful magnetic field. Presumably only some proportion of that would go through our 3nM OIII filter. Would we in fact do better with a wideband blue filter? Ordinarily we'd just give it a try, and all would be revealed, but what with Christmas, Cloud, and Crispy Electronics, it's been a struggle.

Field is cropped to only 9.3 min arc. Total exposure 9 hrs in 1hr subs. Aspen CGC16M on 20" PlaneWave.

Best
a slightly crabby
M & T