Mercury

With snow blanketing the high country, and me without either snowshoes or decent waterproof boots, there’s not much climbing going on lately. But early 2007 brought a very nice evening apparition of Mercury, and at a time when Venus had just returned to the evening sky as well. So I decided to head out around sunset on clear evenings near the 7th of February--Mercury’s date of greatest eastern elongation--and try to snag a decent picture of two of both inner planets in the evening sky.

To minimize logistic problems, I used a decent (not superlative, but decent) observing site just a short walk from home. It’s amazing: From the house, surrounded by trees and within Cheyenne Cañon, the sky near the western horizon is almost totally hidden, and planet watching is virtually impossible. But just a few blocks to the north, just out of the cañon, is the relatively new Stratton Open Space park. The eastern part of it, while not actually flat, consists of gently rolling hills, plus it’s far enough back from all the mountains to the west that the horizon is considerably that the horizon at home, and there are no trees. So, while it’s far from a perfect observing site, it’s much, much better than the back yard, and only six or seven minutes away on foot.

After a little casual looking around, I staked out a site near the crest of one of those hills, marked by a convenient-to-sit-on rock, with the lowest western mountain skyline I could arrange, to use for all my photographic attempts on this venture. The site is located at 38°47’51.47’’N, 104°51’26.86’’W.
My first outing was fully two weeks before the elongation date, when sunset still before 5 pm. I bundled up and headed out just a few minutes after that, and found that I had a long wait. Finally, at nearly 5:30, I spotted Venus (the brighter and higher of the two planets) shining through the sunset glow above the summit of Mt. Rosa. But there was no sign of the dimmer Mercury. I waited until about 5:50, as the sky slowly darkened, until I was sure that Mercury must already have set. This wasn’t an unexpected calamity. Mercury’s appearances are always brief. It rises away from the sun quite rapidly, stays somewhere near its maximum of 22° from the sun for just a few days, and then plunges back out of sight just about as fast as it appeared. So I came away from that first try with a better handle on how early it made sense to go out.
The next clear evening was the 28th of January. This time, I had the foresight to check a couple of online astronomy sites to get approximations of the angular distance between Venus and Mercury, as well as Mercury’s setting time. I knew this last datum would only serve as a rough guideline, since astronomical setting time is when an object reaches the theoretical horizon, 90° from the zenith, and my actual horizon was nowhere near that low. Further, since I didn’t know just how many degrees of sky I was actually losing to the mountain skyline (nope, no sextant!), all I could be sure of was that Mercury would be lost to me, spotted or not, somewhat earlier than its astronomical setting time. I would just have to guess at how much earlier.
By the 28th, sunset was after 5:00, so I didn’t bother going out until about 5:15. Venus came into view almost immediately, farther north than before and higher off the horizon. But still, there was no sign of Mercury by 5:45, when I gave it up.

The 29th was clouded out, but the the 30th was clear. On that date, I was finally able to see Mercury with my naked eye. I spotted it at 5:30, very low to the horizon, and by 5:33--after I had snapped a handful of test photos--it had set. After downloading and inspection, the photos clearly showed Venus, but did not register the presence of Mercury.

Cloudy evenings continued to plague me. I made a few brief visual sightings of Mercury in the ensuing days, but nothing that would photograph. Then, finally, the evening of the 5th of February arrived with clear skies, and I was pretty sure I would finally get something. I snapped nearly two dozen shots that evening, having about twenty minutes to observe Mercury before it set. Despite the fact that I used a monopod mounting to steady the camera, only two of those shots were sufficiently blur-free to be worth keeping. The photo above is what I recorded, just two days before elongation.

Both the 6th, and the 7th, the actual elongation date, brought clouds in the late afternoon, so there are no pictures from those dates. A quick look at my charts, however, confirmed that on the 8th, Mercury would still be almost as far above the horizon as it had been the day before. Thus, I ventured back to my observing site that evening, finding some of the clearest skies to date.

Again, however, focus continued to be my biggest problem, given the long exposure times needed in the failing light. The scene was gorgeous, with the two planets only about 5 degrees apart, but I only managed to get one good photo. As luck would have it, it was the sole one I had taken without zooming in as far as my camera would go, which had become my default mode. Thus, this photo shows more blank sky and horizon than the others. Still, it might be the best one of the whole lot, so here it is: (Yes, Mercury is really in there, right of center and just above the horizon.)



Mercury and Venus will be together in the evening sky later this year, in late May and early June. The geometry, however, will probably not be as good for northern hemisphere observers, and, once again, the Moon will be at the wrong phase to join them in the western twilight. I plan to try taking some pictures all the same, but there’s a good chance that what’s here will still turn out to be the best for the year. And, hopefully, by then, there will be some actual climbing news to report!

Long life and many peaks--