Dominic Ford, Editor
From the Eclipses feed
The Moon will pass through the Earth's shadow between 14:25 and 18:19 EDT, creating a total 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, Australia, New Zealand and Papua New Guinea.
It will not be visible from Cambridge since the Moon will be beneath the horizon at the time.
The total eclipse will last from 15:30 until 17:13. The Moon will be partially eclipsed between 14:25 and 18:19 (all times given in Cambridge 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.
When the Moon's disk lies entirely in shadow, it often takes on a spectacular reddy-brown color, as some of the Sun's red light is bent around the edge of the Earth's globe by its atmosphere.
Sequence of events
The eclipse will begin at 13:15, 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 14:25, 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.
Eventually the Moon will pass entirely within the Earth's umbra at 15:30, and the total eclipse will begin.
The table below lists the times when each part of the eclipse will begin and end.
|13:15||17:15||Moon begins to enter the Earth's penumbra|
|14:25||18:25||Moon begins to enters the Earth's umbra. Partial eclipse begins.|
|15:30||19:30||Moon fully within Earth's umbra. Total eclipse begins.|
|16:22||20:22||Midpoint of eclipse|
|17:13||21:13||Moon begins to leave the Earth's umbra. Total eclipse ends.|
|18:19||22:19||Moon fully outside the Earth's umbra. Partial eclipse ends.|
|19:28||23:28||Moon leaves the Earth's penumbra|
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.
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 July 27 will be visible.
This eclipse is a member of Saros series 129. The exact position of the Moon at the midpoint of the eclipse is as follows:
|Object||Right Ascension||Declination||Constellation||Angular Size|
The coordinates above are given in J2000.0.
|The sky on 27 July 2018|
14 days old
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)
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You can download it from:
|19 Jul 2018||– Moon at First Quarter|
|27 Jul 2018||– Full Moon|
|04 Aug 2018||– Moon at Last Quarter|
|11 Aug 2018||– New Moon|
© John Buonomo, North Billerica, MA.