14 September 2006

2003 UB313, A.K.A. Xena, now has an official name. It has been appropriately named Eris after the goddess of discord in Greek mythology.

BBC story

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I looked at the libration diagrams in Sky & Telescope today to determine when would be favorable times to observe Mare Orientale during the next few months. While doing that I pulled out old issues of the magazine to see if I could discern any sort of pattern. Maximum and minimum libration alternate on about a 7-day cycle going around the moon in a clockwise direction. Maximum libration always occurs around 10:30 and 4:30 and minimum libration around 1:30 and 3:30 on the full Moon’s disc.

Date	2:30 Minimum	4:30 Maximum	7:30 Minimum	10:30 Maximum
1May06		9.0°
8May06			1.4°
15May06				8.3°
22May06	0.5°
29May06		8.4°
4Jun06			1.3°
11Jun06				8.2°
18Jun06	1.4°
25Jun06		8.2°
1Jul06			1.2°
8Jul06				8.8°
15Jul06	2.1°
22Jul06		8.7°
29Jul06			0.9°
5Aug06				9.6°
11Aug06	1.7°
18Aug06		9.6°
25Aug06			0.3°
2Sep06				10.1°
8Sep06	0.6°
14Sep06		10.4°
22Sep06			0.3°
29Sep06				9.9°
6Oct06			0.7°
12Oct06				10.4°
19Oct06	0.9°
27Oct06		9.1°
Maximum	2.1°	10.4°	1.4°	10.4°
Average	1.05°	9.06°	0.89°	9.37°
Minimum	0.5°	8.2°	0.3°	8.2°

There is a discontinuity in the movement of libration around the limb of the Moon in October. From May through early October it has gone around the clock in a clockwise direction every 6-7 days. In October it appears to have regressed 45° and then picked up its normal rotation again. I suspect that this is an error on Sky & Telescope’s part.

Based on six months worth of data it appears that libration is the least in the area of Mare Orientale.

7Oct06 looks like it would be the best day to observe Mare Orientale, but it is New Moon that day. And that is also the date when it looks to me like the data is in error.