© Collin Grady from Las Vegas, Nevada.

Partial lunar eclipse

Dominic Ford, Editor
From the Eclipses feed

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




The Moon will pass through the Earth's shadow between 19:14 and 20:12 EST, creating a partial 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 Cambridge in the south-eastern sky. The Moon will lie 7° above the horizon at the moment of greatest eclipse.

Maximum eclipse will occur at 19:43, when 6% of the Moon's disk will lie in shadow (all times given in Cambridge 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, making the Moon's disk appear entirely unilluminated.

By default the eclipse is drawn with the local vertical in Cambridge 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 Cambridge.

Observing the eclipse

Eclipses of the Moon are easy to watch with the unaided eye. A modest pair of binoculars will give a superb view of the Moon's surface, but are not required. Unlike solar eclipses, lunar eclipses are entirely safe to look at without the need to look through any kind of filter.

They 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.

Sequence of events

The eclipse will begin at 17:28, when the Moon first enters a region of the Earth's shadow called the penumbra. In this outer part of the Earth's shadow, an observer on the Moon would see the Earth partially obscuring the Sun's disk, but not completely covering it. As a result the Moon's brightness will begin to dim, as it is less strongly illuminated by the Sun, but it remains illuminated.

At 19:14, the edge of the Moon's disk will enter the Earth's umbra. This is the region of space in which an observer on the Moon's surface would see the Earth completely obscuring the whole of the Sun's disk, and would find themselves suddenly thrust into darkness.

As an increasing fraction of the Moon's face creeps into the Earth's umbra, we see our planet's circular shadow sweep across the face of the Moon.

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

Local
time
UTC
17:2822:28Moon begins to enter the Earth's penumbra
19:1400:14Moon begins to enters the Earth's umbra. Partial eclipse begins.
19:4300:43Greatest eclipse
20:1201:12Moon fully outside the Earth's umbra. Partial eclipse ends.
21:5702:57Moon leaves the Earth's penumbra
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 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 May 15 will be visible.

Map of where the eclipse of May 2041 will be visible.
Map of where the eclipse of May 2041 will be visible. Click here to expand.

Further information

This eclipse is a member of Saros series 141. The exact position of the Moon at the moment of greatest eclipse is as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 15h29m -19°55' Libra 31'18"

The coordinates above are given in J2000.0.

The sky on 17 September 2019
Sunrise
06:24
Sunset
18:50
Twilight ends
20:26
Twilight begins
04:49

18-day old moon
Waning Gibbous

89%

18 days old

Planets
Rise Culm. Set
Mercury 07:23 13:20 19:17
Venus 07:12 13:14 19:16
Moon 20:52 02:51 09:15
Mars 05:58 12:20 18:43
Jupiter 13:23 17:58 22:33
Saturn 15:22 19:57 00:35
All times shown in EDT.

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_204105.png

Related news

07 May 2041  –  Moon at First Quarter
15 May 2041  –  Full Moon
22 May 2041  –  Moon at Last Quarter
29 May 2041  –  New Moon

Image credit

© Collin Grady from Las Vegas, Nevada.

Cambridge

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Longitude:
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42.38°N
71.11°W
EDT

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