Archive for July 24, 2017

Some Thoughts on Transient Lunar Phenomena: 1

July 24, 2017 2 comments

As a few of you might know, I have always had a strong interesting in astronomy and related areas of the sciences. In fact, many years ago, I seriously considered a career in astrophysics or something along those lines. In the end, I chose an area of research which was more likely to result in a well paid job. Anyway, the point I am trying to make is that I always had a strong interest in, and considerable knowledge of, areas of science that concern the study of celestial objects- which also explains why I have a much better than average understanding of rocketry, among other things.

But what does any of this have to do with my thoughts on transient lunar phenomena?

Well.. a lot. One of the reasons I became interested in astronomy, you see, was my interest in the moon. While people had visited the moon many years before I was born, it still remains the easiest celestial object to study. This is especially so if you grew up in a semi-urban area with moderate light pollution. While where I grew up was dark enough to catch a glimpse of many objects in the Messier and Herschel 400 List, there were times when I ended up watching the moon for hours at a time- usually waiting for some deep sky object to reach a decent elevation above the horizon.

This brings me the subject of what I was watching on the moon. While the moon has been well-studied and documented for decades, and even before manned exploration, there are many reasons why amateur astronomers still study it. For one, there is a certain thrill to being able to see, with your own eyes, craters as small as a few kilometers across (4-5 km) on something about 0.4 million km away. The limits to what you see on the moon (in terms of size) depends on the aperture of your instrument (Dawe’s limit), location on the moon and lighting conditions.

Then there is the tiny chance that you will witness an example of what is popularly known as transient lunar phenomenon aka TLP. To be fair, TLPs are a bit like the lunar version of UFOs, in that they were for a long time considered to be observational artifacts- otherwise known as people seeing things. And why not.. over the last hundred years, scientists have been almost unanimous that the moon has been geologically dead for a very long time- like a couple billion years, at least. Moreover many moon rocks collected by astronauts in late 1960s and early 1970s appear to be 3 to 4 billion years old.

But before we go further, let us talk about the two major types of TLPs. The first type, which last less than a few seconds and are not controversial involve the effect of meteors (meteorites) impacts on the moon. It is not unheard of, especially if you have a decent sized telescope and lots of time or a continuous CCD recording to occasionally see very tiny flashes of light on the unlit parts of the moon. Over a period of many years and hundreds of hours of observation with a 8-inch aperture telescope, I have seen a few tiny flashes, especially when looking at the terminator of moon.

An early and fortuitous photo of what appears to be a meteorite impact on the moon was taken in 1953 by an amateur astronomer named Dr. Leon H. Stuart. Since then, others have taken many more photos and videos of similar (but much fainter) events on the moon. Basically, any meteorite with a mass between several tens to several hundreds of kilograms hitting the lunar surface can produce enough light to be picked up CCD devices attached to telescopes with an aperture larger than 12 inches (or 300 mm)- if they happen to be looking at the right area. The event Leon Stuart photographed was however likely caused by a much larger meteorite- probably one weighing several tons, if not more.

The second type of TLPs, which are far more controversial and rarer, appear as highly localized and often colored mists frequently accompanied by temporary brightening or darkening of the surrounding area. These events usually last for somewhere between a few minutes to a few hours. Also, they seem to occur far more frequently near certain craters and features on the lunar surface than would otherwise be the case. An example of this second type of TLP photographed by Audouin Dollfus in 1992 can be seen below. Over the decades, more than a few astronomers have reordered such localized and transient changes on the lunar surface- both in photographs as well as other light-based measurements.

So what is going on? Is it evidence of volcanic activity? Or outgassing? or some weird electrostatic phenomenon? could it be all due to unfavorable observation conditions? or something else? My personal favorite explanation for the second types of TLPs involves a version of the outgassing hypothesis. However, as you will in the upcoming part of this short series, it is somewhat different from the most common version of that explanation- and I will go into some detail about my reasoning for choosing that particular one over others.

What do you think? Comments?