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Sic transit mundi

Dave North


“It's no surprise we see weird things such as bridges, canals or cities appearing in the right light.”



In a month where I established beyond any reasonable doubt that I can bore large groups of people, one question did stand out as interesting: What about transient lunar phenomena?

Clearly a lot of people are interested in this issue. If you doubt it, google "transient lunar phenomena" and duck!

Love the term. It's even fun as an acronym. But what it simply means is, what about things that "happen" or "change" on the Moon?

I break them down into three categories: things anybody can see and confirm, things that may reasonably be expected to have happened but are not confirmed, and things that probably didn't happen.

Last month, we had one of those things that probably didn't happen - a crater impact in the 1950s. Turns out it showed up in plates taken as early as 1919, which sort of rules it out.

But every month we have all manner of things that do happen.

Probably the effect I see talked about most often is lunar rays, such as the Hesiodus Ray. These happen when light hits an uneven wall (usually a mountain range) and a ray of light shoots through the gap between peaks.

The classic result is a dark area with a stripe of light running across it: a "ray."

There's even a Predictor for this kind of event at: ... that will tell you when various rays will be visible over the next few months. I'm not really much of a ray fan myself, but I suppose my favorite is the Faye Ray (if for no other reason than the pun).

There are many other similar kinds of events, almost always caused by extremely low or high light (the latter causing extreme reflections and the startling illumination of such craters as Linne - itself famous for "changing" though it has not done so since modern photography started monitoring it).

Some people even include eclipses as TLPs. Why not? They're lunar, they're transient ...

Then we have some fairly famous events such as new craters, or gas emissions in the area of Aristarchus or Ptolemaeus. Though some of the observations may turn out to be legitimate, they are generally called into question because of the singularity and incompleteness of the observation (and data).

On this same subject, there's good evidence that some folks did use a clever way to see craters "formed" on the Moon. By watching the dark side during meteor storms, it's possible to see the flashes of impacts as larger particles "touch down."

There's no surprise there - it's just a clever idea that paid off.

However, most of the more sensational observations are either unconfirmed or outright hooey. I'm not sure why some become famous and others drift into obscurity, but the same seems to be true of joke and celebrities. Let's just assume there's some reason and go on from there.

For those who are truly interested, NASA maintains a database of observations of such events at It runs from 1540 through 1969; I'm not sure why it stops there (but we can guess!)

Such things as the idea that the Blair Cuspids are artifacts of an ancient civilization seem downright silly. (The "ancients" are a common theme in these stories - perhaps we finally know where the Anasazi went). Other less unlikely sightings, such as gas emissions, may have some validity. The problem is, there's not much that can be confirmed and much that could just be ...

... some strange effect of light angles and terrain.

Both are extraordinary on the Moon, from our earthly point of view.

There is no air to cause light to diffract or soften; all edges are very hard.

The surface is mostly dark, and dry to an extent that is simply beyond anything on earth. This means crystal faces can get aligned in all kinds of uncharacteristic ways, dark material can heat up remarkably, etc.

On top of that, the terrain itself is curious in that there are virtually no sharp peaks. There's almost no tectonic or volcanic activity on the Moon (nothing significant that we've seen), so the surface is pretty static. Over millions and millions of years, it has been worn to a fine, rounded dustypebbly consistency by the constant bombardment of small particles (such as the meteors that we see every night) and particles ejected by the sun.

The Moon very much does not either look or act in familiar ways. It's no surprise we see weird things such as bridges, canals or cities appearing in the right light.

Well, okay, the canals are there. Called rilles, they're the result of ancient volcanism (mostly) and can be seen almost every night. But they don't change, other than lighting effects.

I don't know a single interested Moon observer who doesn't want to see a really solid transient phenomenon, and I regret I haven't managed to duplicate the above observations.

What most of us would like is to see something like the formation of Tycho or Copernicus: a really big crater impact. That would be such fun!

Not much chance, but if you don't look you can't see.

However, it's best to bear this "wish" in mind whenever you hear about the latest amazing thing seen on the Moon: historically, people see what they want to see.

They have found pyramids, bridges, cities ... you name it. You can find articles such as "Roman City In Kepler" and reports of "diminutive bison" seen.

One thing that is fairly clear: the herds and cities were mostly swept away after 1969.

But if I should see any of these things, you'll be among the first to know. I have certainly seen quite a few remarkable and surprising transient light effects, but every last one has turned out to be just that.

But I still want to see a big one hit.


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