Dominic Ford, Editor
From the Eclipses feed
There will be a penumbral eclipse of the Moon, visible from Ashburn in the south-eastern sky. The Moon will lie 20° above the horizon at the moment of greatest eclipse.
The eclipse will last from 21:50 until 00:39, and maximum eclipse will occur at 23:15 (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 31% 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.
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 June 26 will be visible.
The table below lists the times when each part of the eclipse will begin and end.
|21:50||01:50||Moon begins to enter the Earth's penumbra|
|00:39||04:39||Moon leaves the Earth's penumbra|
This eclipse is a member of Saros series 110. The exact position of the Moon at the moment of greatest eclipse is as follows:
|Object||Right Ascension||Declination||Constellation||Angular Size|
The coordinates above are given in J2000.0.
|The sky on 17 July 2018|
4 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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|26 Jun 1991, 23:00 EDT||– Full Moon|
|04 Jul 1991, 22:51 EDT||– Moon at Last Quarter|
|11 Jul 1991, 15:07 EDT||– New Moon|
|18 Jul 1991, 11:12 EDT||– Moon at First Quarter|