MassMutual Jr.Space Camp



When the Earth orbits into a position between the Sun and the Moon, the Earth's shadow (or ‘umbra’) obscures the Moon.

This shadow can be divided into two parts
(i) Umbra: the Moon is in total shadow and not illuminated by sunlight.
(ii) Penumbra: the Moon is in partial shadow, illuminated by a small amount of sunlight.

When the Moon enters the umbra wholly, a total lunar eclipse will occur; similarly, a partial lunar eclipse occurs when only part of the Moon is in the umbra. If the Moon does not enter the umbra but only the penumbra, the lunar eclipse in this situation is called a penumbral lunar eclipse (or ‘partial lunar eclipse’).


When does a lunar eclipse take place?
Lunar eclipses take place when the Sun, the Earth and the Moon are aligned. Hence, this can only occur on the nights of full moon (i.e., on the fifteenth of the lunar calendar). However, as the Moon's orbit is not on the same plane as the Earth's orbit, the Moon does not lie in the Earth's shadow in most full moon situations. Similarly, this phenomenon explains why a solar eclipse does not occur at every new moon.


Is there such a thing as an annular lunar eclipse?
No. As the area of the Earth's umbra is much larger than the Moon, the Moon will be entirely covered by the Earth's umbra. Hence, the phenomenon of an annular lunar eclipse does not occur.


(Image Credit: Hong Kong Space Museum)



Total Lunar Eclipse

When the Moon enters the Earth's umbra, a Partial Lunar Eclipse and a Penumbral Lunar Eclipse will happen before and after a Total Lunar Eclipse.

(A) When the penumbra zones of the Earth and the Moon starts to contact
(B) Partial Lunar Eclipse begins when the umbra zones of the Earth and the Moon contacts with each other
(C) Total eclipse begins when the Moon enters the Earth's umbra zone completely
(D) Middle of eclipse is when the centres of the Earth and the Moon are in the closest distance
(E) Total eclipse comes to the end when the Moon starts to leave the umbra zone of the Earth
(F) Moon leaves umbra zone of the Earth completely
(G) Moon leaves penumbra zone of the Earth completely

Partial Lunar Eclipse
When only a part of the moon enters the umbra of the Earth, a penumbral lunar eclipse will take place before and after the occurrence of a partial lunar eclipse.

(A) When the penumbra zones of the Earth and the Moon starts to contact
(B) Partial Lunar Eclipse begins when the umbra zones of the Earth and the Moon contacts with each other
(D) Middle of eclipse is when the centres of the Earth and the Moon are in the closest distance
(F) Moon leaves umbra zone of the Earth completely
(G) Moon leaves penumbra zone of the Earth completely

Penumbral Lunar Eclipse
When the Moon enters only part of the Earth's shadow, the penumbra, the sunlight reflected by the surface of the Moon is less intense and the rim of the Moon is not totally obscured.

(A) When the penumbra zones of the Earth and the Moon starts to contact
(B) Middle of eclipse is when the centres of the Earth and the Moon are in the closest distance
(C) Moon leaves penumbra
Forthcoming lunar eclipses for 2017 to 2020:
Date 1 Type Hong Kong Hong Kong Time2
11/02/2017 Penumbral Eclipse at Moonset 6:32am - 10:55am
08/08/2017 Partial Visible 1:22am - 3:19am
31/01/2018 Total Visible 7:48pm - 11:12pm
28/07/2018 Total Eclipse at Moonset 2:24am - 6:19am
21/01/2019 Total Invisible 11:34am - 2:51pm
17/07/2019 Partial Eclipse at Moonset 4:01am - 7:00am
11/01/2020 Penumbral Visible 1:06am - 5:14am
06/06/2020 Penumbral Visible 1:44am - 5:07am
05/07/2020 Penumbral Invisible 11:04am - 1:55pm
30/11/2020 Penumbral Eclipse at Moonrise 3:30pm - 7:56pm
  1. The dates shown in the table indicate the time the "Moon enters umbra" or the "Moon enters penumbra".
  2. For Total / Partial lunar eclipses, the time period is for when the "Moon enters umbra" to "Moon leaves umbra". For Penumbral lunar eclipse, the time period is for when the "Moon enters penumbra" to "Moon leaves penumbra".
Penumbral Lunar Eclipse on November 28, 2012
(The above data is provided by Hong Kong Space Museum)
 
 
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