Partial lunar eclipse

2019 Jul 16

The Moon will pass through the Earth’s shadow between 21:02 and 23:59 BST, 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, Asia, Europe, South America and Australia.

It will be difficult to see from London since the Moon will rise partway through the eclipse, and only attain an altitude of 15° above the horizon by the time it ends.

Maximum eclipse will occur at 22:31, when 65% of the Moon’s disk will lie in shadow (all times given in London time).

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. The circular shadow cast by the Earth appears as a bite taken out of the Moon during its partial phases.

Sequence of events

The eclipse will begin at 19:44, 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 Sun 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 21:02, 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, it will appear to have a growing bite taken out of it. We will 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
19:44 18:44 Moon begins to enter the Earth’s penumbra
21:02 20:02 Moon begins to enters the Earth’s umbra. Partial eclipse begins.
22:31 21:31 Greatest eclipse
23:59 22:59 Moon fully outside the Earth’s umbra. Partial eclipse ends.
01:17 00:17 Moon 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 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.

Further information

This eclipse is a member of Saros series 139. The exact position of the Moon at the moment of greatest eclipse is as follows:

Object Right Ascension Declination Constellation Angular Size
The Moon 19h43m -21°55′ Sagittarius 29’56”

The coordinates above are given in J2000.0.

This entry in the observing calendar was provided by In-The-Sky.org

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