May 9th - Mercury Transit - HA & WL - Black Drop?

[paulastro]

      I observed the transit at The Astronomy Centre, where approximately 30 - 40 members and visitors came along at some time.  As predicted the weather was just about perfect with clear skies throughout and generally good seeing.  There were all varieties of solar equipment in use throughout the day.  The event lasted from 12.13 pm to 7.40 pm so it was quite a marathon.  I  used my Lunt 60mm DS with the Olympus E-M5 for HA and my Equinox 80 and Lunt H Wedge for WL.  It was good to have plenty of time for visual observations as well as taking pics approximately every 30 minutes.

The first HA disk was taken at 12.13 and there is a crop from it, which appears to show the black drop - I'd be interested to hear what people think.  The second close-up was taken only a few seconds later and I've included it for comparison.  The second HA disk and close-up were taken around maximum transit, at 3.56pm.  The two white light shots were taken shortly afterwards.

 

 

 

[xtreemchaos]

cracking shots Paul,thay make feel like i saw it myself.thanks  charl.

[Pete Presland]

Not sure be honest looks like you might have done, but a great set of images either way.

[101nut]

I posted in another thread that visually I felt that the Ha 'black drop' effect was insignificant but in white light it hung on for ages.

Not sure with your picture as the surface is so uneven that the 'drop' could just be an undulation in the surface. In Ha I noted that there was an active prominence almost at that point too so the surface was very turbulent. I would suggest 'inconclusive'.

Nice captures though.

AndyG

[Macavity]

Interesting topic. I was initially surprised that no definite conclusion had bean reached.
I had thought it all to be an "atmospheric effect", but...

"We were able to show that the Mercury black-drop effect comes from a convolution
of the instrument's point-spread function and the solar limb darkening" See ref. [1]:
https://en.wikipedia.org/wiki/Black_drop_effect

Clearly there is a significant difference between White Light and H-Alpha images 
- In terms of sharpness alone. I always supposed that was due to differential effects
of atmospheric turbulence effect on the component colours of white light?

[laudropb]

Very nice set of images. Not so sure that is the black drop.

[paulastro]

1 hour ago, 101nut said:

I posted in another thread that visually I felt that the Ha 'black drop' effect was insignificant but in white light it hung on for ages.

Not sure with your picture as the surface is so uneven that the 'drop' could just be an undulation in the surface. In Ha I noted that there was an active prominence almost at that point too so the surface was very turbulent. I would suggest 'inconclusive'.

Nice captures though.

AndyG

Thanks Andy.  I didn't think it was undulation in the surface myself.  Though the spicules do vary in length, I've never seen them  form a concave depression as symmetrical as it  would need to be in this case.  Also, it would be rather convenient for it to form exactly at the time and place where Mercury is starting it's transit.  Of course this by no means indicates it is the Black Drop effect either, I'm interested to hear as many views as possible.  Thanks again.

[David Smith]

A nice crop of images Paul. Glad you had good clear skies for the event.

[paulastro]

1 hour ago, Macavity said:

Interesting topic. I was initially surprised that no definite conclusion had bean reached.
I had thought it all to be an "atmospheric effect", but...

"We were able to show that the Mercury black-drop effect comes from a convolution
of the instrument's point-spread function and the solar limb darkening" See ref. [1]:
https://en.wikipedia.org/wiki/Black_drop_effect

Clearly there is a significant difference between White Light and H-Alpha images 
- In terms of sharpness alone. I always supposed that was due to differential effects
of atmospheric turbulence effect on the component colours of white light?

Thanks Chris, you have some good points there.  Similar to  yourself, I'd always thought it was most likely a mixture of atmospheric turbulence and the affect this has on optical systems.  Interesting non the less.

[paulastro]

8 minutes ago, David Smith said:

A nice crop of images Paul. Glad you had good clear skies for the event.

Many thanks David, it's unusual for us to have the most favoured conditions for an astronomical event.  Usually it a case of the more S or SE toward East Anglia the better.

[paulastro]

2 hours ago, xtreemchaos said:

cracking shots Paul,thay make feel like i saw it myself.thanks  charl.

Thanks charl.  I'm very sorry that you missed out on this occasion.

[michael8554]

Hi Paul

Looks to me that the black drop was forming, I think mercury would have to be just clear of the limb but connected to the limb by the black drop to satisfy the definition.

Michael