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Penumbral lunar eclipse

Dominic Ford, Editor
From the Eclipses feed

A simulation of how the eclipse will appear from Ashburn.
Time:       Altitude: °      Azimuth: °
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.

The Moon will pass through the Earth's shadow between 01:25 and 05:03 EDT, 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, the Americas, Portugal and Cape Verde.

It will be visible from Ashburn in the south-western sky. The Moon will lie 31° above the horizon at the moment of greatest eclipse.

Maximum eclipse will occur at 03:14 (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 54% 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 August 17 will be visible.

Map of where the eclipse of August 2027 will be visible.
Map of where the eclipse of August 2027 will be visible. Click here to expand.

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

01:2505:25Moon begins to enter the Earth's penumbra
03:1407:14Greatest eclipse
05:0309:03Moon leaves the Earth's penumbra

This eclipse is a member of Saros series 148. The exact position of the Moon at the moment of greatest eclipse is as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 21h42m -12°29' Capricornus 29'29"

The coordinates above are given in J2000.0.

The sky on 17 August 2027
Twilight ends
Twilight begins

15-day old moon
Waxing Gibbous


15 days old

Rise Culm. Set
Mercury 06:53 13:39 20:25
Venus 06:29 13:20 20:11
Moon 20:12 01:06 06:25
Mars 11:01 16:39 22:16
Jupiter 07:14 13:52 20:31
Saturn 22:40 05:13 11:43
All times shown in EDT.


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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