Away From The Terminator

by David North

I recently read an article by Jay Freeman extolling the virtues of inspecting the moon away from the terminator -- that geological contrasts are visible in changing light angles. Also, I was perusing an article by Bill Dembrowski about observing lunar rays, also (of course) at high sun angles.

I think both these were on my mind as I was looking with scantily clad eyes at the moon, waiting my turn at the eyepiece.

Scantily clad?

I just got some new contacts that work lotsa well, and I was quite surprised at how much detail I could make out, just looking. The split of Nectaris and Fecunditatis was obvious, as was the extension of Frigoris and the tonalities in the massive Procellarum.

But what really stood out was the darker nature of the surface in the area of Humorum. In fact, my initial impression was a darkness to the north of Humorum, but I broke out my binos and got a slightly better look, only to find I had confused the complex of Lacus Excellentae and Timorus plus Palus Epidemarium with Humorum; the "dark spot" was Humorum itself.

Click.

Just the previous night we had been discussing the incredible colletion of arcuate rilles in these two areas, and speculating that there are perhaps more per square mare mile than anywhere else on the moon.

Now here I was noting a distinct color difference.

This would imply a different mineral mix in the lavas that formed in this area, perhaps more mafic than the other mare materials -- which may also imply a greater tendency toward the kind of shrink faulting presumed to cause these rille complexes.

This is idle speculation at this point, and there's no telling if I'll ever find the time to chase it down in any detail.

Still, it makes a good argument that there are other places to look than the terminator, and interesting things to see all the time.

It may be that mooning is only -- and always -- as interesting as the ideas that drive the observation.