© Collin Grady from Las Vegas, Nevada.

Partial lunar eclipse

Dominic Ford, Editor
From the Eclipses feed

Objects: The Moon

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




The Moon will pass through the Earth's shadow between 08:45 and 11:40 EDT, creating a partial lunar eclipse. The eclipse will be visible any location where the Moon is above the horizon at the time, including from Antarctica, Asia, Russia and Oceania.

It will not be visible from Cambridge since the Moon will be beneath the horizon at the time.

Maximum eclipse will occur at 10:13, when 68% 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 shows the Moon's position in the sky relative to the horizon, as seen from Cambridge.

Timing

The eclipse will begin at 07:32, 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 08:45, 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 thrust into night-like 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
07:3211:32Moon begins to enter the Earth's penumbra
08:4512:45Moon begins to enters the Earth's umbra. Partial eclipse begins.
10:1314:13Greatest eclipse
11:4015:40Moon fully outside the Earth's umbra. Partial eclipse ends.
12:5416:54Moon leaves the Earth's penumbra
The geometry of a lunar eclipse
The geometry of the Earth's shadow. Within the Earth's penumbral shadow, the planet covers some fraction the Sun's disk. Only within the smaller umbra does the Earth cover the entirety of the Sun's disk. Any areas of the Moon's surface that pass through the penumbra appear darker than usual as the Earth is obstructing some of the sunlight that usually illuminates them. Areas within the umbra, meanwhile, receive no illumination from the Sun at all.

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.

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 6 will be visible.

Map of where the eclipse of August 1990 will be visible.
Map of where the eclipse of August 1990 will be visible. Click here to expand.

The eclipse geometry

Lunar eclipses occur when the Sun, Earth and Moon are aligned in a straight line, so that the Earth passes between the Sun and Moon and casts a shadow onto the latter's surface.

Each time the Moon orbits the Earth, it passes almost opposite to the Sun in the sky as it reaches Full Moon. If the Moon orbited the Earth in exactly the same plane that the Earth orbits the Sun, the Earth would pass between the Sun and Moon and create a lunar eclipse at Full Moon every month.

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 fact, the Moon's orbit is tipped up at an angle of 5° relative to the Earth's orbit around the Sun. This means that the alignment of the Sun—Earth—Moon line at Full Moon usually isn't exact. As a result, an observer on the Moon would see the Earth pass a few degrees to the side of the Sun.

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 this Earth–Sun plane twice each month, at the points on the left and right labelled as nodes. A lunar eclipse happens only when one of these node crossings happens to coincide with Full Moon. This happens roughly once every six months, usually two weeks before or after a solar eclipse.

Further information

This eclipse is a member of Saros series 138. The position of the Moon at the moment of greatest eclipse is as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 21h05m 16°03'S Capricornus 30'47"

The coordinates above are given in J2000.0.

Next/previous eclipses

« Previous Next »
Visible from the Contiguous United States Worldwide Worldwide Visible from the Contiguous United States
27 Aug 1988 27 Aug 1988 Partial Lunar Eclipses 21 Dec 1991 21 Dec 1991
17 Aug 1989 09 Feb 1990 Lunar Eclipses 30 Jan 1991 30 Jan 1991
17 Aug 1989 22 Jul 1990 Eclipses 15 Jan 1991 30 Jan 1991

The sky on 12 Dec 2024

The sky on 12 December 2024
Sunrise
07:02
Sunset
16:11
Twilight ends
17:52
Twilight begins
05:20

11-day old moon
Waxing Gibbous

95%

11 days old

Planets
Rise Culm. Set
Mercury 05:48 10:39 15:30
Venus 10:10 14:51 19:33
Moon 13:54 21:23 05:05
Mars 19:24 02:53 10:22
Jupiter 15:41 23:11 06:41
Saturn 11:44 17:16 22:48
All times shown in EST.

Source

[1] – 

The lunar eclipse predictions presented on this website were computed using EphemerisCompute.

This is an open-source tool which traces the positions of the Sun, Earth and Moon over the course of each eclipse and traces the path of the Moon through the Earth's shadow. It was written by the author and freely available for download from GitHub.

It takes the positions of each body from the JPL DE430 planetary ephemeris.

[2] – 

Espanak, F., & Meeus, J., Five Millennium Canon of Solar Eclipses: -1999 to +3000, NASA Technical Publication TP-2006-214141 (2006)

[3] – 

The list of countries from which the eclipse is visible was computed on the basis of shape files available from DIVA-GIS.

License

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_19900806.png

Related news

29 Jul 1990  –  Moon at First Quarter
06 Aug 1990  –  Full Moon
13 Aug 1990  –  Moon at Last Quarter
20 Aug 1990  –  New Moon

Image credit

© Collin Grady from Las Vegas, Nevada.

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