LTP Checklist for Color

The following are based upon the flow charts in Appendix 2 of the “Hatfield SCT Lunar Atlas – A digitally Re-mastered Edition”.

Definition: A “Color LTP” is where part of the lunar surface exhibits color that is not normally seen there. However it is very easy to be deceived by color e.g. chromatic aberration in the optics, from spectral dispersion in our own atmosphere, and from natural colour on the lunar surface. Note however that any colored LTP should be short term in duration, whereas all the other effects described above either change over a long period of time, or are permanent.

Checks to do: You should follow these steps to eliminate non-LTP causes:

1) Are there any other lunar features with similar colored effects? If yes it is not an LTP.

2) Is the effect perpendicular to the horizon and less prominent when the Moon is higher above the horizon? If yes then it is due to atmospheric spectral dispersion.

3) If the color is on bright/dark edges it may still be due to atmospheric spectral dispersion.

4) Now check for chromatic aberration in the optics – move the lunar feature concerned around the field of view and see if the amount, or direction, of the colour varies. If it does then it is not a LTP. A yellow filter may help in the case of refractors to reduce chromatic aberration. For color CCD cameras an IR blocking filter is essential.

5) If this is a visual observation, use red and blue/green filters, e.g. Kodak Wratten 25 and 44a. If it is bright in one filter and dark in another – in comparison to the surrounding terrain, then goto step 6, else it is not a LTP.

6) If the effect is blue and the crater is Aristarchus, or it is orange/yellow and on the floor of Bullialdus, then it is natural surface colour. If you have time examine quickly on-line color lunar images in case they exhibit similar color to what you have seen, and if so then it is not an LTP.

7) Beware, if the Moon is low, you may get some flashing colours on bright spots, which are not LTP.

8) If the color is seen in Earthshine, and not on the dayside, and it is not Aristarchus crater exhibiting some blueness, then it may well be a real LTP.

Observing a Colored LTP: You should do as many of the following, in the suggested order, and do these as quickly as possible because many LTP are short duration events:

1) Quickly telephone, text, or email the LTP coordinator so that other observers can be mobilized.

2) Briefly check on the appearance of the color, write a description, or take an image.

3) Quickly telephone, text, or email a few astronomy colleagues to mobilize them – but do not tell them what you have observed else this will bias their observation.

4) Return to the telescope and sketch what you see, or take images (in color if possible), at regular intervals until the LTP vanishes. This will help us put a limit on the duration and development of the event. If the effect does not vanish after an hour or more, then it becomes less likely that it is an LTP.

5) If observing visually, use red, blue, green, or Polaroid filters to see how the effect appears ?

6) From time to time see if other similar contrast features exhibit any color, especially on edges?

7) When the nights observing is over, write up your report, including images and sketches and email to the LTP coordinator. Please try to write the report as quickly as possible in case you forget details.

ALPO LTP coordinator: Dr Anthony Cook. Tel/Text +44 798 5055 681. Email: atc @ aber.ac.uk