This past Veterans Day the tiny planet Mercury was scheduled to cross the face of the Sun in an event visible in its entirety from my vantage point in North America. Such alignments are infrequent yet not as rare as those when we get to see Venus interposed between us and the Sun; we get two of those within a decade and then the interlude is over a century before the next transit pair. For Mercury we get to witness roughly 13 such events in a century. Like any celestial phenomena that takes place in under 12 hours, not every point on the globe gets to see the transit - in some locales the entire event happens while the Sun is below the horizon (a.k.a. night time).
I've been fortunate enough to catch a couple of prior Mercury transits. My first was on Saturday May 9, 1970, just about two months following the amazing total Solar Eclipse for the east coast that took place on March 7th. My notes have long since been lost on that event but I do recall seeing the tiny dot of our smallest planet against the Sun using my RV-6 Newtonian using a solar filter by the same company. The next transit that I have a clear memory of (and some notes) was Monday May 9, 2016. It's not just coincidence that both are on May 9th - the orbital mechanics dictates that a transit of Mercury can only occur within a couple days of May 8th or November 10th when Mercury's orbit intersects Earth's plane. If Mercury happens to be undergoing inferior conjunction at that time we have ourselves a transit.
Looking at the predictions for Mercury transits beyond 2019 showed that while there was one set for 2032 and another in 2039 neither would be visible from my side of the planet. That makes the next candidate May 7, 2049 - putting me well into my nineties. So for me the reality was that the November 11th event would be my swan song for any planetary transits. In a year that brought several reminders of my own mortality here was the universe offering yet another commentary upon it.
I decided to try to make this last Mercury transit the best yet. The prediction for 1st contact was 7:35 a.m., which meant the Sun would be quite low in the sky. If I could find a suitable location I might be able to witness that 1st contact and maybe even the "black teardrop" effect. But a more realistic goal was to try to obtain some nice photographic captures of the tiny orb as it marched its way across old Sol. I planned to take the RV-6 on the Atlas mount with me and the Canon Rebel t6s camera and the DFK21AU042 planetary video camera. I gathered everything together the evening before and then fashioned a solar filter using some Baader solar film, sandwiching it between stiff cardboard. The weather forecast was iffy - most prognostications had high clouds moving in as the morning wore on. I set out the equipment so that when I got up it would be easier to load it into the Rogue and set off in search of a venue with good eastern horizon.
The pre-dawn was not encouraging. While portions of the sky were clear the eastern direction had a buildup of high altitude clouds - the Sun was clearly not going to penetrate it. Regardless I set off looking for a location. I toyed with the idea of heading to the parking lot at Leidos where I work. It would be pretty empty on Veterans Day (a government holiday) and the horizon is pretty good. But the commute could be 30 minutes or more meaning the transit would likely be underway by the time I made my own transit and got set up. In the end I set up on the western edge of the ball field by the BYKOTA senior center in Towson, trying to position myself to catch the Sun soon after it rose. I had used the spot before in 2004 to catch the Venus transit soon after sunrise.
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| Setup outside BYKOTA, waiting for clouds to disperse |
The 1st and 2nd contacts came and went without my witnessing them, a combination of clouds and obstructing building. Finally by about 8 a.m. the clouds thinned just enough that I could target the Sun using the shadow technique. I popped in the 16mm Plossl and focused. It took a moment but then there it was - a tiny black silhouette of planet Mercury against a solar disk completely devoid of sunspots. Yay! I could at least say I had successfully witnessed my third transit of Mercury!
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| Fighting clouds & buildings at the start |
My initial attempt to record the phenomena was with the DFK21AU042 video imager, but it proved a frustration. With the Sun over my shoulder making it hard to see the screen and focus at the same time I was not getting any worthwhile results. I switched to the 35mm camera adapter for eyepiece projection using the 16mm and the camera's live view mode, working to bring the solar limb into sharp focus. Even though I finally got to what seemed to be a good sharpness it was challenging to see if the view contained the tiny dot of planet Mercury. Without any sunspots that could serve as landmarks to guide me to position the best I could do was approximate, My approach evolved into taking a shot, bringing it up for review and enlarging it on the tablet to see if I by chance had caught the messenger planet. If not I used the RA/Dec control pad to slew to another part of the Sun to take another shot. It took a little while but finally ended up with a pretty decent image of the transit.
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| Mercury Transit - ISO 400 at 1/15 sec using 6" f/8 with 16mm Plossl |
As I worked to get some photos there was a gradual stream of dog walkers, joggers, and curious neighbors wondering what the heck was going on. I obliged most of them with a peek through the scope so that they could tell friends and family they had seen it. By a little before 9 a.m. I decided to pack up and head home to finish observing and capturing the transit. I was back in business on the driveway of 404 within about a half hour, setting up the Vixen 80mm as well so that I could take some whole disk shots of the Sun sporting Mercury. The clouds continued to threaten - in the short video below you can see them crossing the face of the Sun. There were a few times when the clouds won but surprisingly the bulk of the transit window the Sun was visible.
Around 10:30 a.m. I decided to start taking a set of bracketed shots of the whole disk every 15 minutes in the hopes of creating a final product that would document the tiny speck making its way towards 3rd contact. I got most of the shots but the 10:45 one was a bit out of focus. It was quite challenging to get a sharp focus on the Samsung tablet that was connected to the Canon due to the Sun making it hard to see the screen. I resorted to having a pillow case draped over my head every 15 minutes as I tried to recenter the Sun and check the focus.
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| Mercury marches across the Sun on Nov. 11, 2019 (times EST) |
As we slid past noon the tablet was running low on battery, signaling that photography would soon be over. I took a few more looks at the tiny, silhouetted dot to appreciate the scale of things in our solar system. As the clouds began to thicken yet again I decided to conclude observations and began to breakdown the setup. I may have missed the ingress and egress but overall it was a fine and memorable event to mark my last planetary transit!
