NavList:

Jacquelin Hardy, yuo wrote:
"What tools do we have ? Differential GPS ? Sextant ? Quartz  watch ? Almanac ? One eye ?  Two eyes ? 10 x 80 binoculars ? No tool ?"

More toole... Fewer tools... as you deem necessary to make an interesting demonstration of finding longitude by a lunar eclipse.

Two specific scenarios you might consider: 

1) You have a pair of NavList members separated by some degrees of longitude. Both observers have sextants, above-average math skills (or at least computation skills!), an adequate watch, binoculars, ...and clear skies. For that pair of observers, how can you determine the difference in longitude between them?

2) You are a teacher working remotely (online) with a science-enthusiast young person, let's say "middle school", equipped with good, basic computation skills, some basic algebra, and brains enough to understand the difference between working something out by internet and working it out by observation. Also you can assume binoculars, maybe a small telescope, a fair watch, ...and clear skies.  How could that single observer determine the true longitude of the observing location, given the UT of the start and end times of the partial eclipse?

For both scenarios, you can also assume a couple of days of prep. If the student needs to spend some time learning a constellation or two, you can allow that.

The problem with some accounts of longitude by lunar eclipse is that students are merely told to "time" these events. The start time of this partial lunar eclipse is 2:33 UT, and the end is 5:52 UT. If we "time" those based on common civil time (zone time) will be hh:33 and hh:52 since, with some exceptions, like Newfoundland, the UT offset to civil time is an exact integer (whole number) of hours. So everywhere in Eastern Time (US and Canada) and other aligned time zones, the eclipse will begin at 10:33pm regardless of longitude --if you're within the EDT zone.

Frank Reed