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Transit of Mercury

Posted: 9 May 2016

On three previous occasions I have been able to observe and twice photograph a Transit of Mercury. The first was 9 May 1970 as I was completing my senior year in Astrophysics at Indiana University. I was part of a small group that observed the transit using a 6" reflector telescope. Some of us independently made an unusual observation. Two of us conferred with our solar astronomy professor about it, and then we submitted our report to Sky and Telescope magazine, which published the report in the July 1970 issue. You can read the report here. The second transit was on 15 November 1999 when I used my Meade ETX-90RA. The third was on 8 November 2006; used the ETX-90RA and Coronado PST. I also observed and photographed the 5 June 2012 Transit of Venus using the PST, ETX-90RA, and a Meade 8" LX200-ACF. The 9 May 2016 Transit of Mercury was already in progress when the Sun rose over the hill east of Cassiopeia Observatory.

Open: Monday, 9 May 2016, 0532 MST
Temperature: 53°F
Session: 958
Conditions: Clear, breezy

Equipment Used:
12" f/8 LX600 w/StarLock
Wireless AutoStar II handset
Solar Filter

D7200 DSLR

0544 MST: 12" LX600 ON, StarLock OFF. Mounted the D7200 DSLR at prime focus + visual back + focal reducer. Added the full-aperture solar filter.

Slewed to the Sun (using the "Sun as Asteroid" AutoStar object). I would focus the Sun's image on the camera once it rose over the hill.

Just prior to the Sun appearing I took this photo of the setup:


0608 MST: sun rose over the hill. Focused and began imaging using 1/100sec, ISO 100, White Balance. As the Sun rose higher in the sky I increased the shutter speed up to 1/1000sec in steps. I did images every 15 minutes until 3rd Contact approached when I did images more frequently, finally doing them every 15 seconds. Here is a sequence of images:

0645 MST:

0915 MST:

1045 MST:

1138 MST:

113929 MST:

As the transit progressed I would observe it through the DSLR viewfinder:


1120 MST: moved the observatory dome onto the PZT to continue imaging as the Sun was nearing the Zenith.

The final image was taken at 1142 MST.

I have assembled the images into this 39 second video clip:

Click or tap on image for video

Close: Monday, 9 May 2016, 1158 MST
Temperature: 85°F
Session Length: 6h 26m
Conditions: Mostly clear, breezy

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