BAA Lunar Section

Dedicated to amateur research and observation of the Moon


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Transient Lunar Phenomena

By Dr Anthony Cook


Is the Moon now completely inactive or do some geological processes/events still happen, and are these visible from Earth?

Conventional geologic wisdom accepts that lunar volcanism ceased ~1 billion years ago. Although cratering is ongoing, it is at such low levels that new craters are generally too small to be seen from Earth, except for the moment of impact when they let off a flash of light.

However past research and observations by amateurs, and professional planetary scientists/astronomers, have proven that changes and effects have taken place on the Moon very recently, and are sometimes visible from the Earth. These can take the form of short duration brightness changes, obscurations, coloured glows and flashes of light.

Position of ~2000 TLP reports from 554 AD to 2008.
The spot area indicates frequency of reports for the feature concerned.

In the US Bill Cooke of NASA’s Marshall Space Flight Center has a set of robotic telescopes that he is using to monitor the dark side of the Moon for impact flashes. To date over 100 have been recorded on low light sensitive video cameras.

Also based in the US, Arlin Crotts of Columbia University has been operating a robotic telescope in Cerro Tololo, Chile, and other world wide locations, to monitor the Moon’s surface in white light, every few seconds to look for changes. He has proposed a theory that many TLP are caused by episodic releases of Radon gas during moon quakes that erupt from the surface through cracks. This raises dust temporarily and increases reflectivity in the short term. His team makes ~300 hours of observations per month but have yet to analyse their results.

This is an outline the present observing programme of the BAA and ALPO Lunar Section TLP teams.

Anybody interested in participating should contact

Observing programme 1
Obtain detailed sketches, or high resolution images of certain lunar features under the same illumination and/or libration to what they were like in past TLP observations.

We constrain 'same illumination' to mean within +/-0.5° solar selenographic longitude and latitude with respect to the original event.

We constrain 'same illumination and libration' to mean within +/-1° of both solar selenographic and libration longitude and latitude with respect to the original event.

These repeat illumination/libration observations of a feature can tell us whether what was reported as a TLP was normal or not.

Current observing opportunities:
Lunar features and original descriptions of TLPs that have occurred there.

Observing programme 2
Look for impact flashes on the Moon’s night side

Using low light level CCTV cameras, such as those used typically for occultation timings, in order to record typically < 0.1 sec duration impact flashes.

Using integrating CCD cameras, to take time lapse images of the Earthshine, to look for evidence of debris from impacts making it into sunlight and becoming visible e.g. SMART-1.

Current observing opportunites:
Earthsine observing times and meteor showers and also TLP target sites.

Observing programme 3
Monitor frequently, Ina type features and their surrounds

Pete Schultz of Brown University has proposed that Ina (see figure opposite) structures on the lunar surface are geologically recent (perhaps only 10 million years old) and so might still occasionally out-gas.

So it makes sense to observe close to such areas for evidence of coloured glows, brightenings, and obscurations, which might indicate outgassing

Observing programme 4
Monitor the terminator and crater shadow interiors for glows

Look for evidence of coloured glows from Radon gas being ionized in sunlight, as seen against a dark background.

Look for evidence of optical scattering off clouds of electrostatically levitated dust particles on the terminator, again utilizing the dark background to help detect these – polaroid filters may help here.

The observation opposite remains a puzzle. There are no breaks in the crater rim that could allow sunlight to reach the central peak. It may be possible that the peak was being illuminated by secondary scattered light off the illuminated rim, but there is no evidence of other parts of the floor being illuminated too.

Observing programme 5
Monitor large areas of the lunar surface using time lapse video

This can replicate Arlin Crotts work in the US except that this can be done through narrow band filters, specific to emission lines that one might expect from out-gassing e.g.
Radon e.g. 705nm, 745nm, 810nm, 860nm
Argon e.g. 764nm, 811nm, 840nm
Sodium (often contributes to the lunar atmosphere after an impact) e.g. 589nm
Hydrogen e.g. 656nm

Above: 860nm and 840nm images of the Aristarchus area. No obvious signs of differences.

The narrower the waveband, the more sensitive the equipment will be to these specific lines

25mm diameter interference filters (10nm FWHM) can be purchased from companies such as Edmund Optics or Knight Optical for ~70 pounds each.

Assuming that the seeing is good and the Moon does not drift too much, then computer difference imaging can be used to detect changes

Above: 'Simulation' of a change in brightness TLP on two Clementine images (left and middle image). Differences detected (on right) — blue signifies 3 standard deviations and red 8 standard deviations

Observing programme 6
Monitor the lunar surface visually using an Electronic Moonblink device

This is similar to the previous strategy but the human observer can be brought into the loop for interactive detection of TLP.

Different filters narrow band filters can be switched into the optical path for say 1 second before moving onto the next.

The narrow band filters should be similar in wavelength to avoid having to refocus.

A low light CCTV camera looks through each of the filters.

The observer monitors the Moon on a television monitor looking for parts of the lunar landscape that 'blink', indicating emission in one waveband and not in the other.

This technique is ~an order of magnitude or two more sensitive to colour from the specific emission lines than the human eye alone.

Above: An Electronic Moonblink device.

Searching for very young lunar geological features
The latest LROC (Lunar Reconnaisance Orbiter Camera) images allow the Moon's topography to be searched in great detail in order to identify features that may be geologically very young. Click on the link below to download a PDF file Curious Vents, Cracks and Other Signs of Recent Change on the Moon by TLP Coordinator Dr Anthony Cook, which describes various types of suspected young features and how they may be identified.