Observing Mercury

In recent times, knowledge of Mercury has greatly increased. In the early 1990s, researchers detected ice in the perpetual cold of polar craters. Currently, the MESSENGER probe is mapping the innermost planet and searching for signs of water. Of course, amateurs can't advance our understanding of Mercury. But they can see it themselves.

I first tried over forty years ago. In late March 1971, my lack of experience showed. Taking "just after sunset" too literally, I began looking when the sky was still too bright. Not until the following year did I see it. On March 6, 1972, Mercury appeared as a scintillating speck below three other planets--Venus, Mars and Saturn--in the west.

Since then finding Mercury has been routine. Most amateurs see it during March or April, when the ecliptic is at its highest in the west after sunset. Last month, I saw the little orb on eight evenings. Five of them were after greatest eastern elongation, which occurred March 22. On March 28, for the first time, I saw Mercury six days after GEE. Of course, it was much dimmer then than it was ten days earlier. I knew it would dim as it approached inferior conjunction, prior to vanishing from the evening sky. For me, the denouement of this appearance was unusual. On March 28, it seemed brighter when I first spotted it than it was a short while later. The next evening, the 29th, I thought I saw it, but when I paused to switch to a higher magnification eyepiece, I was unable to find it again (assuming I really saw it). Such an experience is counterintuitive. Mercury should appear brighter as time passes and twilight deepens. I wonder if others have had this experience.