LTP Checklist for Dayside Brightenings

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

Definition: An “Dayside Brightening” is where a part of a lunar feature, or a spot, appears brighter than it should do, or where no bright spot has been seen before. Be careful though as this requires the observer to have familiarity with that part of the Moon under all phases. Also sunward facing slopes on mountain peaks emerging from shadow, can look very bright, so too can sun lit peaks at the north and south poles

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

1) Check some images of the area in an atlas, or on-line, quickly – try to find ones under similar illumination. If the suspect area looks similarly bright, then it is not LTP.

2) Compare the brightness to other similar sized features at the same distance from the terminator. If you find ones of similar brightness, and similar solar slope direction, then it may not be not a LTP.

3) Could the cause of the brightening be due to vignetting effects in the eyepiece? Move the telescope field of view around to see if that explains the brightening. If so it is not a LTP.

4) Is it a small feature – the brightness may vary with seeing conditions – but this will affect other similar sized features too.

5) Have you checked to see if any cloud is passing across the Moon? Fine structure in the cloud can affect some features more than others.

6) Beware that Mons Piton and Mons Pico at sunrise, and a spot on the NW rim of Mare Crisium create a lot of false alarms with reports of bright spots.

Observing an Dayside Brightening LTP: If the above suggest it might be a LTP, then 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 LTP brightness, and 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, just the name of the lunar feature. This will avoid observational bias.

4) Return to the telescope and sketch what you see, or take images, at regular intervals until the LTP vanishes. This will help us put a limit on the duration and development of the event.

5) Compare its brightness to other similar sized features over time i.e. one fainter, and one brighter and deduce what fraction in brightness it lies between these two.

6) If observing visually, try to see if there is any color, or whether it is brighter in red, green or blue filters.

7) When the night’s 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