Transient Lunar Phenomena

by Nancy Thomas

Transient lunar phenomena (TLPs) also known as lunar transient phenomena (LTPs)
can range from seeing color or brightness changes to an observer possibly
seeing a haze or mist develop or even a lunar feature obscured for a short
time. Some observers have reported seeing glows on the lunar surface while
others have reported seeing flashes. While I have never had the privilege of
witnessing such an event the thought of such a phenomena is something I find
quit interesting. Apparently, the first reports of such a phenomena were
recorded in 1783 and since then, over 1200 sightings have been made. The most
famous and documented report was made in 1958 by Nikolai Kozynev who observed
the crater Alphonsus emitting something gaseous in nature, which turned out to
be, carbon and nitrogen. What the astronomer observed was a reddish glow that
lasted a few minutes. Since that time, amateur astronomers have paid just a
little more attention to the possibility of seeing such a phenomena for
themselves.

Other areas of the lunar surface involved are the craters Aristarchus, Plato,
Gassendi, Fracastorius, Theophilus, Grimaldi, Kelper, and Hercules. One might
also pay attention to areas around edges of regular maria and rills as these
areas seem to be prone to TLPs. Also, it seems TLPs are more apt to be reported
when the moon is at perigee and this is because of the great gravitational
stresses acting on the moon. According to one source, the crater Aristarchus
has been the scene of about 300 sightings, while there have been over 70 near
Plato, and 25 around Alphonsus. These figures are not current, however.
Sensitive instruments on Apollo recorded an emission of radioactive radon gas
near the vicinity of Aristarchus and at the edges of some circular maria.
Otherwise, the lunar astronauts reported seeing nothing in the way of TPLs.
However, the Apollo 17 astronauts did come across patches of orange soil that
would cause a "Moon Blink" device to reveal a blink, but more on this later. At
present, it seems that TLPs are caused by escaping gases from beneath the lunar
surface. Some have even suggested that TLPs are caused by solar activity. In
the past, one might have considered the cause to stem from temperature change,
broken ground, dilution of shadow by reflected light, clouds of dust blown up
by escaping gases, and grazing illumination. Seismic equipment has recorded
some activity going on in the areas where TLPs have been reported, so, this
shows that the moon isn't such a dead and inactive world after all! It is also
thought that such seismic activity is converted into visible light and that is
why observers see the glows and flashes. One source has suggested that flashes
might be caused by meteorites striking the lunar surface in a darkened area.

While there are those that believe the observation of TLPs requires an
experienced observer I believe the beginner can do just as well by becoming
VERY familiar with the area he wishes to keep under observation. So, how does
an observer go about observing TLPs. After the observer has become thoroughly
familiar with the area to be studied the next step would be the utilization of
colored filters. One source lists Kodak Wratten filters No. 25 (red) and 80A
(blue) as the ones to use for the observations of TLPs. With the filters one
can construct a "Moon Blink" device that uses rotating red and blue filters,
plus a clear patch. (More information, on this device, can be found in the book
entitled, The Amateur Astronomer Handbook, by James Muirden, 1983, p. 111). The
feature that the observer wishes to study is viewed in quick succession with
any red area showing up as "winking patch". If one thinks he/she might have
observed a TLP, the next step would be to try and examine other formations in
the area. It is also, at this point, where more than one observer would be
helpful in verifying the presence of a TLP. A r\group of observers working
together would be of great help and is referred to as a mutual alert system.
(As always, the observer should try and make a sketch of the suspected TLP
outlined on a photograph, noting time, weather conditions, instrument used
along with other essential data.) Be aware of the fact that some "TLPs" might
be caused by such things as defective optics, or the type of instrument
(achromatic refractors can give a bluish color to the edges of Aristarchus and
the same is somewhat true of reflectors) also, eyepieces can have some false
color to them. Dirt, atmospheric conditions on Earth, the effects of light and
shadow, and even earthshine can also be cause of some false TLPs. Summary As
noted in the Atlas of the Moon, by Antonin Rukl, this field of study requires
much in the way of time, patience, dedication, a solid knowledge of the lunar
surface, and a high quality telescope that is fairly large in size. Perhaps,
with a little luck, the amateur will be rewarded for his/her efforts and spot a
TLP!

Nancy Thomas is now "on line" at NLTsolar@aol.com