Jupiter from 8-9 october, jetstream or poor seing

[ONIKKINEN]

With 8'' f/4.4 newtonian, 678MC + paracorr and 2.5x barlow, resized to 75% of capture size. 3 minute capture with best 5% of almost 35k frames stacked in AS!3:

Jupiter appeared soft, but no jumpiness in the recording. Just poor seeing or a jetstream in the way i think and due to that focusing was challenging and im not sure it was ideal. There was a wide range of focuser positions where i could not tell the difference if i made it better or worse.

Meteoblue claimed a 1'' fwhm seeing overhead, but a seeing index of 1 (the worst), so not sure how to interpret that as the fwhm value and seeing index are in contradiction. It was a bit misty on ground level too, which may have had a local effect.

 

Edited October 9, 2022 by ONIKKINEN

[vlaiv]

1 hour ago, ONIKKINEN said:

Meteoblue claimed a 1'' fwhm seeing overhead, but a seeing index of 1 (the worst), so not sure how to interpret that as the fwhm value and seeing index are in contradiction. It was a bit misty on ground level too, which may have had a local effect.

It can happen.

In that case - image will be steady but you won't be able to focus properly.

FWHM is measure of average displacement of star from its position and it is good mostly as indicator of seeing for long exposure. It tells you nothing of how "violent" that disturbance/displacement is.

If such disturbance is bending image slowly - then we call that a good seeing (since it is small in magnitude and moves slowly). You can then freeze it in short exposure and have no blur (only mostly distortion) in single frame. If it is very high frequency motion - it will simply present as blur, as even at very short exposure, you won't be able to freeze it - point will move left/right/up/down multiple times although with small magnitude - but enough to cause blur that can be frozen (at least not with reasonable exposure time).

FWHM can be though of as sound loudness, while seeing can be both low and high pitch sound. Low pitch is better for imaging and observing than high pitch sound - even if not it is not that loud.

[ONIKKINEN]

4 minutes ago, vlaiv said:

It can happen.

In that case - image will be steady but you won't be able to focus properly.

FWHM is measure of average displacement of star from its position and it is good mostly as indicator of seeing for long exposure. It tells you nothing of how "violent" that disturbance/displacement is.

If such disturbance is bending image slowly - then we call that a good seeing (since it is small in magnitude and moves slowly). You can then freeze it in short exposure and have no blur (only mostly distortion) in single frame. If it is very high frequency motion - it will simply present as blur, as even at very short exposure, you won't be able to freeze it - point will move left/right/up/down multiple times although with small magnitude - but enough to cause blur that can be frozen (at least not with reasonable exposure time).

FWHM can be though of as sound loudness, while seeing can be both low and high pitch sound. Low pitch is better for imaging and observing than high pitch sound - even if not it is not that loud.

I did deep sky imaging after planetary/lunar and found that the seeing was nothing special, not too much in either direction of average and not nearly as bad as i felt it was just minutes ago with the lucky imaging so this makes sense now. Thanks for the useful explanations as always!

[Pete Presland]

Looks a pretty good image to me, despite the difficulties in focussing