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Penumbral lunar eclipse

Sat, 25 May 2013 at00:11 EDT(1734 days ago)
04:11 UTC

Dominic Ford, Editor
From the Eclipses feed

Time:       Altitude: °      Azimuth: °

A simulation of how the eclipse will appear from Ashburn.

The outer grey circle is the Earth's penumbra, and the inner black circle is the umbra. Any part of the Moon which passes within the black circle will be unilluminated, while any part within the grey circle will appear less bright than usual.

There will be a penumbral eclipse of the Moon, visible from Ashburn in the southern sky. The Moon will lie 29° above the horizon at the moment of greatest eclipse.

The eclipse will last from 23:54 until 00:27, and maximum eclipse will occur at 00:11 (all times given in Ashburn time).

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 begin to dim, as it is less strongly illuminated by the Sun, but the whole of the Sun's disk will remain illuminated to some degree.

Although the Moon's light dims considerably during a penumbral eclipse, this is only perceptible to those with very astute vision, or in carefully controlled photographs.

Moreover, on this occasion no more than 1% of the Moon's face will pass within the Earth's penumbra, even at the moment of greatest eclipse, making it especially difficult to notice any reduction in the Moon's brightness.

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 entirity 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.

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 May 25 will be visible.

Map of where the eclipse of May 2013 will be visible.
Map of where the eclipse of May 2013 will be visible. Click here to expand.

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

23:5403:54Moon begins to enter the Earth's penumbra
00:1104:11Greatest eclipse
00:2704:27Moon leaves the Earth's penumbra

This eclipse is a member of Saros series 150. The exact position of the Moon at the moment of greatest eclipse is as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 16h09m -19°23' Scorpius 33'15"

The coordinates above are given in J2000.0.

The sky on 25 May 2013
Sunrise 05:48
Sunset 20:23
Twilight ends
Twilight begins

15-day old moon
Age of Moon
15 days

All times shown in EDT.
Rise Culm. Set
Mercury 06:39 14:12 21:45
Venus 06:43 14:10 21:37
Moon 21:17 01:08 06:05
Mars 05:20 12:29 19:38
Jupiter 07:00 14:24 21:47
Saturn 17:46 23:13 04:43


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

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Related news

18 May 2013, 00:36 EDT  –  Moon at First Quarter
25 May 2013, 00:26 EDT  –  Full Moon
31 May 2013, 14:59 EDT  –  Moon at Last Quarter
08 Jun 2013, 11:58 EDT  –  New Moon

Image credit

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