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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 19:05 and 22:14 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 Africa, the Americas, Asia and Europe.

It will be visible from Ashburn in the south-eastern sky. The Moon will lie 5° above the horizon at the moment of greatest eclipse.

Maximum eclipse will occur at 20:40 (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 40% 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 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 August 5 will be visible.

Map of where the eclipse of August 2009 will be visible.
Map of where the eclipse of August 2009 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
19:0523:05Moon begins to enter the Earth's penumbra
20:4000:40Greatest eclipse
22:1402:14Moon 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 21h02m -15°33' Capricornus 29'31"

The coordinates above are given in J2000.0.

The sky on 22 February 2019
Sunrise
06:51
Sunset
17:53
Twilight ends
19:22
Twilight begins
05:22

18-day old moon
Waning Gibbous

87%

18 days old

Planets
Rise Culm. Set
Mercury 07:33 13:25 19:17
Venus 04:40 09:32 14:25
Moon 21:51 02:48 08:54
Mars 09:22 16:11 23:01
Jupiter 02:36 07:21 12:06
Saturn 04:27 09:14 14:01
All times shown in EST.

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_200908.png

Related news

28 Jul 2009  –  Moon at First Quarter
05 Aug 2009  –  Full Moon
13 Aug 2009  –  Moon at Last Quarter
20 Aug 2009  –  New Moon

Image credit

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