M45 Pleiades Cluster 27-11-11

[Carole]

My 2nd image from that lovely clear night on Sunday.

31 x 300sec 800 ISO, Modified Canon 450D, CLS filter
Skywatcher ED120 Pro, guided with PHD and ST 80
Using APT for the first time but PHD was not linked to APT (not got that far yet, tried to link it later and the whole thing froze on dithering, I don't think I have quite set it all up correctly yet, so a job for next time).

Processed in DSS and PS CS3

One interesting feature is the long spike on Alcyone.  I seem to be starting to get long single spikes on bright stars (see the HH image), but this one is the longest yet and I don't have a spider.  I have examined all the subs and every one has it (very faintly) so it can't be a satellite.

[mickw]

Have you cropped and rotated the image ?
Does the line correspond with a plane of the camera ?

Nice image by the way

[Carole]

No Mick, this is exactly how is came out the the camera, no cropping or rotation at all.

Carole

[RobertM]

and I don't have a spider

Have you checked recently ?  If the spike's been growing then the spider must be doing well   Tony knows all about spiders but wouldn't recommend them; spiders and scopes don't mix very well...

Robert

[MarkS]

Which HH image are you referring to?  The Andromeda Galaxy image?

Was the orientation of the spike the same?

[Carole]

HH = Horsehead.

No the orientation of the spike is slightly different.
DSLR not moved between the two images.

Carole

[MarkS]

It's probably a stray hair or similar moving around, probably inside the camera body or maybe around the flattener.

Mark

[Carole]

Well it's strange that it seems to locate itself right over a bright star twice on the same evening in different places.

Anyway, I quite like a few spikes, so I'm not complaining.  So no scientific/photographic explanation then? 

Carole

[MarkS]

Well it's strange that it seems to locate itself right over a bright star twice on the same evening in different places.
Anyway, I quite like a few spikes, so I'm not complaining.  So no scientific/photographic explanation then? 

The hair does not have to be directly in the path of the star. Each star on the CCD has a cone of light going to it from the lens.  Every star whose cone of light is cut by the hair will inherit a diffraction spike.  So the futher the hair is from the CCD, the more stars it will affect.  At the extreme, a hair (or spider) in front of the scope will affect every star.  The fact that only 1 star is affected indicates that the hair must be reasonably close to the CCD.

[mickw]

So Carole is moulting ?   

[Carole]

Well at least it saves putting an artificial spider in front.  I always envied people with Newtonians and SCTs as they always get spikes and I didn't and I quite like them but hesitate to put them on artificially.

Carole

[mickw]

but hesitate to put them on artificially.

Quite right too, for they are Satan's Spikes 

[Carole]

Ah, well I had better not post this one I tarted up for the Home page on my website then. 

[mickw]

Oi I said Satan's Spikes, not Santa's Spikes

Merry Christmas 

[Carole]