Total Lunar Eclipse October 27/28

Geoff Gaherty, Toronto Centre


There will be a total eclipse of the Moon beginning on the evening of Wednesday October 27 visible all across Canada.  The Moon will pass through the upper part of the Earth's shadow, being totally eclipsed for 1 hour and 21 minutes. Details of the eclipse can be found in the Observer's Handbook 2004, pages 137 to 149. This material is also available on the internet at:

http://sunearth.gsfc.nasa.gov/eclipse/OH/OH2004.html

A lunar eclipse is an astronomical event that can be observed and appreciated without any optical aid whatsoever, and photographed with ordinary cameras, though binoculars, a telescope, or a camera with a telephoto lens can enhance the experience.

The Earth's shadow consists of two parts: the dark central part, where the Sun's light is completely blocked by the Earth, called the umbra; and the outer lighter part where only part of the Sun's light is obscured, called the penumbra. The colour of the eclipsed Moon is influenced by weather activity along the Earth's terminator: if it is mainly cloudy, most of the Sun's rays will be blocked and the eclipse will be relatively colourless and dark; if clear, the light reaching the Moon will be tinged with sunsets, leading to an orange or red colour. When the Moon enters the penumbra, the shading is imperceptible, but darkens as the Moon moves towards the umbra.  In comparison, the edge of the umbra is usually a well defined line, and it's possible to time when this edge enters and leaves the Moon's surface, as well as the times when it obscures various craters. Such timings provide information about the size and shape of the Earth's shadow in this particular eclipse.

Eclipse times

The eclipse is visible at exactly the same time all across the country, though local times differ because of time zones. What does differ is the local time at which the Moon rises. The following table gives times for all the time zones across Canada, and approximate times of moonrise for each:

Event
NDT
ADT
EDT
CDT
MDT
PDT

Moonrise
Moonrise
Moonrise
Moonrise
Moonrise

Penumbra 1st contact
21:36
21:06
20:06
19:06
18:06
17:06






Moonrise
Umbra 1st contact
22:44
22:14
21:14
20:14
19:14
18:14
Umbra 2nd contact
23:53
23:23
22:23
21:23
20:23
19:23
Greatest eclipse
00:34
00:04
23:04
22:04
21:04
20:04
Umbra 3rd contact
01:15
00:45
23:45
22:45
21:45
20:45
Umbra 4th contact
02:24
01:54
00:54
23:54
22:54
21:54
Penumbra 4th contact
03:33
03:03
02:03
01:03
00:03
23:03

Thus, except in western of Canada, the Moon will have risen before the first imperceptible beginnings of the Moon entering the penumbra. The Moon will be above the horizon all across the country when the dark umbra first touches the Moon. After fourth contact with the umbra, the reddish shading of the penumbra will gradually leave the Moon until it is imperceptible at fourth contact.

Observations

A lunar eclipse is one of Nature's most beautiful events, and can be simply enjoyed for its own sake, whether with naked eye, binoculars, or a small telescope. In fact, in viewing a lunar eclipse, less is more. It can also be photographed with all but the simplest cameras. If you attempt photography, remember to reduce the exposure recommended by your camera to enhance the colour of the eclipse. If you have any filter on your lens, even a protective one, remove it to avoid ghost reflections. I neglected that advice while photographing a lunar eclipse once, and ended up with a ghost Moon in every shot!

There are at least two kinds of observations which can be made which are of scientific value during a lunar eclipse. One is to estimate the colour and darkness of the eclipse at its greatest extent using the Danjon Scale of Lunar Eclipse Brightness. This estimate is best done either naked eye or with low power binoculars. Another is to estimate, to the nearest tenth of a minute, the time when individual craters are eclipsed or emerge from eclipse. Fred Espenak has provided a table of suitable craters and the approximate time when they will be covered and uncovered on page 145 of the Handbook; this table is also available on the web. Be sure to use Table 4 on this page, as Table 2 refers to the May 4 eclipse. Identifying craters at full Moon is often very difficult because the lunar surface appears quite different than it does at other phases. It helps to first identify a few prominent bright craters, such as Tycho, Copernicus, and Aristarchus, and well defined dark areas like the Mare Crisium and the Sinus Iridum, and then locate smaller features relative to them. A simple map, like the one on page 117 of the Handbook, is actually easier to use at full Moon than a larger, more detailed map or atlas. Unfortunately, this map doesn't include some of the smaller craters in Espenak's list, so you will need to add them from another map. An ordinary watch synchronized with a time signal or an accurate computer clock is adequate to record contact times to the nearest 1/10 of a minute. Because the edge of the Earth's shadow is ill defined, lower magnifications are actually more useful than high powers for making these timings, since the shadow will appear sharper. Thus, a powerful binocular or low power telescope is actually the best tool for observing a lunar eclipse.
 
Revised 2004-10-13