A Check in the Box

The 2016 Transit of Mercury

Yesterday was the last Transit of Mercury until 2032, and the first one observed by me.

Although the event started shortly after sunrise, Maryland time, I didn't arrive at Alpha Ridge Park until about 8:30. But it only took 5 minutes to set up, and another minute to find that unbelievably tiny spot, already almost one quarter of the Sun's angular diameter from the edge. What a difference from the Transit of Venus seven years ago. Venus' disk was large enough that you needed no magnification to see it against the Sun. A pair of properly shielded "eclipse" glasses would suffice. Not so yesterday! I tried spotting it through another member's 8X56 binoculars and couldn't see a thing, even though I knew exactly where Mercury ought to be.

But with my Stellarvue 60mm refractor, I had no trouble seeing Mercury, despite its miniscule size. Using my 9mm Nagler eyepiece, it remained a dimensionless point of un-light, but switching to my 5mm Nagler, it was a definite disk. It almost looked 3 dimensional.

In addition to the Baader solar filter safety attached to the business end of my scope, I inserted a Televue Mars filter between the diagonal and the eyepiece, which gave the Sun's disk a pleasing yellow/orange hue, a definite improvement over the otherwise unfiltered pure white.

Image by James Willinghan

Notice how small Mercury appears against the Sun (slightly above the center of disk)
(To see at full resolution, click on the image.)

Now you might say that sitting for 5 hours tracking a nearly dimensionless black dot as it crawls across the face of a featureless Sun (I was hoping for a few sunspots, damn it!) would be about as exciting as watching paint dry... and in a way, you would be right. But only in a way, for as with most things in amateur astronomy, it all depends on how you look at it.

First of all, there is the obvious but strangely overlooked fact that all this is going on in broad daylight. That, and the fact that the Sun was fairly low in the sky (it being late autumn), had a curious effect of rotating one's vertical axis of perception. The Sun and Mercury were not "up there" but rather "over there". I was acutely conscious of being in the plane of the ecliptic, along with all the other planets. And that perception somehow made what was going on more comprehensible to my Earthbound brain. Mercury was not merely crossing in front of the Sun, it was crossing "left to right" - not above me, but in front of me. I was part of the action! This is an awareness hard to arrive at when admiring a view of the Hercules Globular or the Rosette Nebula, or even Jupiter or Saturn. (It's easier with the Moon, but that's another story. See here: Explorers and here: Explorers 2.) I could clearly visualize the geometry of all the moving parts, and where I fit into it.

Secondly.. well, has it ever occurred to you how often we refer to this rather eclectic group of planets, moons, asteroids, as the Solar System, but fail to take in the meaning of that term? The planets are not just, as was thought in Percival Lowell's time, "other worlds" - they are OUR world. All the planets and everything else that makes up the Solar "System" are intricately and inextricably connected to each other. The Earth does not exist in isolation. In fact, our planet would be uninhabitable were it not for, not only Jupiter, but also Saturn being where they are. And some theories say we would have no oceans without there being a Kuiper belt. Etc, etc. Watching Mercury pass between the Earth and the Sun reminds me of this interconnectivity.

(And it reminds me of my own interconnectivity with the rest of humanity. See here: Foxholes)

And thirdly, it makes me acutely aware of the role of chance in our lives. As I look out the window at this moment, only 24 hours after the event, I see a 100% overcast sky with high winds and mixed snow and rain. Yet yesterday, despite depressing forecasts, was mostly clear with low winds and shirtsleeve temperatures. Had today been yesterday, we wouldn't have seen a thing.

So it's one more "check in the box", along with the 1985 return of Halley's Comet, the 2012 Transit of Venus, the 2017 total solar eclipse, and the 2018 opposition of Mars. The next will be the Great Conjunction of Jupiter and Saturn in Aquarius on December 21, 2020. If I've done my math right, the two planets will be separated by an angular distance of only one fifth of the full moon!