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Penumbral lunar eclipse

Dominic Ford, Editor
From the Eclipses feed

Simulation of the eclipse as seen from Seattle
Time:       Altitude: °      Azimuth: °




The Moon will pass through the Earth's shadow between 04:16 and 08:52 PST, creating a penumbral lunar eclipse. The eclipse will be visible any location where the Moon is above the horizon at the time, including from Oceania, Asia, Northern America, Eastern Europe, Aland Islands, Ethiopia and Somalia.

It will be visible from Seattle in the western sky. The Moon will lie 9° above the horizon at the moment of greatest eclipse.

Maximum eclipse will occur at 06:34 (all times given in Seattle time).

The simulation to the right shows Moon's path relative to the Earth's shadow. The outer grey circle is the Earth's penumbra, within which the Earth blocks part of the Sun's light, making the Moon appear less bright than usual, but not completely dark. The inner black circle is the umbra, within which the Earth entirely blocks the Sun's light, and where the Moon's disk would appear entirely unilluminated.

By default the eclipse is drawn with the local vertical in Seattle uppermost (Zenith up), so that it is orientated as you would see it looking up at the Moon. The compass shows the direction of celestial north relative to the local vertical. Alternatively, you can orientate the sky with celestial north orientated uppermost, by selecting the option North up.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

Selecting the option Diagram of Moon's path produces a static display of the Moon's path over the duration of the eclipse.

The lower panel of the simulation shows the Sun's position relative to the horizon as seen from Seattle.

A penumbral eclipse

Like other lunar eclipses, penumbral eclipses occur whenever the Earth passes between the Moon and Sun, such that it obscures the Sun's light and casts a shadow onto the Moon's surface. But unlike other kinds of eclipses, they are extremely subtle events to observe.

In a penumbral eclipse the Moon passes through an outer region of the Earth's shadow called the penumbra. This is the outer part of the Earth's shadow, in which the Earth appears to cover part of the Sun's disk, but not all of it (see diagram below). As a result, the Moon's brightness will be reduced, as it is less strongly illuminated by the Sun, but the whole of the Moon's disk will remain illuminated to some degree.

The effect is only perceptible to those with very astute vision, or in carefully controlled photographs.

This is a rare occasion when the whole of the Moon's face will pass within the Earth's penumbra, and so the reduction of the Moon's brightness will be more perceptible than usual. Such events are called total penumbral lunar eclipses, and are rare because the statistical chance that the Moon will enter the Earth's umbra at some point is very high once it has passed fully within its penumbra, and this makes an eclipse a partial lunar eclipse.

The geometry of a lunar eclipse
The geometry of a lunar eclipse. Within the penumbra, the Earth covers some fraction of the Sun's disk, but not all of it. In the umbra, the Earth covers the entirety of the Sun's disk. Any parts of the Moon's surface that lie within the Earth's umbra will appear unilluminated. Image courtesy of F. Sogumo.

The eclipse geometry

Lunar eclipses occur when the Sun, Earth and Moon are aligned in an almost exact straight line, with the Earth in the middle, such that the Earth casts a shadow onto the Moon. The diagram to the right shows this geometry, though for clarity the Moon is drawn much closer to the Earth than it really is.

The Moon passes close to this configuration every month, when it is at full moon, but because the Moon's orbit around the Earth is tipped up by 5° relative to the Earth's orbit around the Sun, the alignment of the three bodies into a straight line usually isn't exact.

The Moon's orbit is tipped up by 5° relative to the Earth's orbit around the Sun, represented by the grid above. Lunar eclipses only occur at full moon if they occur when the Moon is close to the Earth–Sun plane, at points called the Moon's nodes.

In the diagram to the right, the grid represents the plane of the Earth's orbit around the Sun. As it circles the Earth, the Moon passes through the Earth–Sun plane twice each month, at the points on the left and right labelled as nodes. A lunar eclipse results when one of these node crossings happens to coincide with full moon, which happens roughly once every six months.

Visibility of the eclipse

Eclipses of the Moon are visible anywhere where the Moon is above the horizon at the time. Since the geometry of lunar eclipses requires that the Moon is directly opposite the Sun in the sky, the Moon can be seen above the horizon anywhere where the Sun is beneath the horizon.

The map below shows where the eclipse of November 28 will be visible.

Map of where the eclipse of November 2012 will be visible.
Map of where the eclipse of November 2012 will be visible. Click here to expand.

The table below lists the times when each part of the eclipse will begin and end.

Local
time
UTC
04:1612:16Moon begins to enter the Earth's penumbra
06:3414:34Greatest eclipse
08:5216:52Moon leaves the Earth's penumbra

This eclipse is a member of Saros series 145. The exact position of the Moon at the moment of greatest eclipse is as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 04h19m +20°26' Taurus 29'23"

The coordinates above are given in J2000.0.

The sky on 28 November 2012
Sunrise
07:32
Sunset
16:20
Twilight ends
18:11
Twilight begins
05:42

15-day old moon
Waxing Gibbous

99%

15 days old

Planets
Rise Culm. Set
Mercury 05:46 10:43 15:39
Venus 04:55 10:02 15:09
Moon 16:48 00:31 07:21
Mars 10:09 14:15 18:20
Jupiter 16:30 00:20 08:05
Saturn 04:43 09:55 15:08
All times shown in PST.

Source

Espanak, F., & Meeus, J., Five Millennium Canon of Lunar Eclipses: -1999 to +3000, NASA Technical Publication TP-2009-214172 (2009)

You may embed the map above in your own website. It is licensed under the Creative Commons Attribution 3.0 Unported license, which allows you to copy and/or modify it, so long as you credit In-The-Sky.org.

You can download it from:
https://in-the-sky.org/news/eclipses/lunar_201211.png

Related news

20 Nov 2012  –  Moon at First Quarter
28 Nov 2012  –  Full Moon
06 Dec 2012  –  Moon at Last Quarter
13 Dec 2012  –  New Moon

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