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Transit of Mercury (and Clouds)

Posted: 11 November 2019

Cloudy skies continued on Tuesday, 5 November 2019. Before sunrise Wednesday morning, 6 November, had a brief thundershower (0.02") with lots of lightning, as seen in these webcam photos.

photo photo
photo photo

Thursday, 7 November, was mostly overcast. That morning I had planned to do a dry run for the Transit of Mercury which occurs on Monday, 11 November, but the clouds prevented it. My next opportunity to do a dry run was Sunday, 10 November, as I attended the International Dark-Sky Association (IDA) Annual General Meeting (AGM) on Friday and Saturday. I was a panelist on Saturday. When I arrived home after the AGM Saturday night, the waxing gibbous Moon was visible high in the sky with a full 22° halo around it:


Sunday, 10 November, was overcast so I was not able to do a Transit dry run then. The forecast for Monday during the Transit of Mercury was for a partly cloudy sky and Monday, 11 November, did dawn mostly cloudy.

Hoping that I would be able to get some images of Mercury in front of the Sun I decided to open the observatory anyway. Mercury was already about half way through its pass across the Sun. This would be my fifth attempt at viewing a Transit of Mercury. The previous four were all very successful: 9 May 1970 while a student at Indiana University, 15 November 1999 with an ETX-90RA, 8 November 2006 with the ETX-90RA and PST, and 9 May 2016 with the 12" LX600.

Open: Monday, 11 November 2019, 0751 MST
Temperature: 57°F
Session: 1404
Conditions: Party cloudy

Equipment Used:
12" f/8 LX600 w/StarLock
2" 24mm UWA eyepiece
Solar Filter
Focal Reducer

iPhone 11 Pro Max

Upon arrival at the observatory the sky towards where the Sun woud rise over the hill looked like this:


I SYNCed the observatory clock to WWV time signals. I then attached the Thousand Oaks Optical Solar Filter to the 12" telescope.

0758 MST: the Sun appeared over the hill to the southeast.

0800 MST: LX600 ON, StarLock OFF, High Precision OFF.

0802 MST: did a GOTO the Sun using the "Sun as Asteroid" AutoStar object. Viewed the Sun and Mercury in transit, 102X. No sunspots were visible on the Sun. 0804 MST: grabbed this quick handheld iPhone 11 Pro Max afocal 102X image of Mercury near the middle of the Sun's disk with the Sun still behind a tree.


0806 MST: viewed the Transit of Mercury using the Lunt SUNoculars (8x32). I viewed the transit frequently with the SUNoculars.

Mounted the D850 DSLR at prime focus, with and without the visual back extension. The Sun's entire disk would not fit in the field-of-view (FOV). Had I been able to do a dry run in the days leading up to the transit I would have known this, but the clouds and AGM prevented doing a dry run. I knew it would be a close fit as I knew what the angular diameter of the Sun would be and what the DSLR FOV is. I switched to the focal reducer for imaging the Sun's entire disk. Set the DSLR clock to the observatory clock.

This is the set up.


0828 MST: took this (uncropped) image of the Sun (1/640sec, ISO 400; all DSLR photos used this exposure setting) showing small Mercury near the middle of the Sun's disk. Mid-transit was at 0819 MST. Focusing was a challenge due to the small scale of Mercury and poor seeing through tree limbs. Even using Live View on the DSLR screen did not help. Focusing continued to be a challenge throughout the transit.


I planned to image the Sun every 15 minutes from 0845 MST to 1100 MST, then exposures every 30 seconds 110200-110430 MST to capture Contact III (110233 MST) and Contact IV (110414 MST).

0845 MST: the Sun cleared the tree and there were no clouds near the Sun. Began imaging. As the morning progressed clouds would occasionally approach and even cover the Sun. 0922 MST: this photo shows clouds in the northwest sky that were approaching the observatory.


This photo shows the Sun and sky reflected in the solar filter.


A view of the sky towards the Sun with clouds over the Sun.


And a selfie at the 12" telescope viewing the transit through the DSLR viewfinder.


1000 MST: this photo (cropped) shows how the Transit of Mercury appeared with a lot of clouds in the way.


1051 MST: took a final look at the Sun using the SUNoculars. Mercury was now too close the Sun's limb to be seen using only 8X magnification.

1101 MST: breezes began picking up.

1105 MST: ended imaging.

I merged several photos (except the 1000 MST one with the clouds) for this image of the Transit of Mercury.


The appearance of a wiggle in the path of Mercury is due to focus changes throughout and aligning errors for the Sun's disk.

The clouds mostly cooperated and it was fun to observe the Transit of Mercury once again. The next one is in 2032, but won't be visible from Cassiopeia Observatory.

1106 MST: LX600 OFF.

Close: Monday, 11 November 2019, 1121 MST
Temperature: 87°F
Session Length: 3h 30m
Conditions: Partly cloudy, breezy

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