Lunar Eclipses

A Lunar eclipse occurs when the Sun casts Earth’s shadow onto the Moon. For this to happen, the Earth must be physically between the Sun and Moon with all three bodies lying on the same plane of orbit. A lunar eclipse can only occur during a Full Moon and when the Moon passes through all or a portion of Earth’s shadow.

Geometry of a Lunar Eclipse

Schematic diagram of the shadow cast by the Earth. Within the central umbra shadow, the Moon is totally shielded from direct illumination by the Sun. In contrast, within the penumbra shadow, only a portion of sunlight is blocked.

The outer portion of the shadow cast from Earth is known as the penumbral shadow, which is an area where Earth obstructs only a part of the Sun’s light from reaching the Moon.  The umbral shadow is the “inner” shadow, which is the area where Earth blocks all direct sunlight from reaching the Moon.  A penumbral lunar eclipse is subtle and very difficult to observe.  A partial lunar eclipse is when a portion of the Moon passes through the Earth’s umbral shadow.  Finally, a total lunar eclipse is when the entire Moon passes into the Earth’s umbral shadow.  During a total lunar eclipse, the sequence of eclipses are penumbral, partial, total, partial and back to penumbral.

Unlike solar eclipses, a total lunar eclipse lasts a few hours, with totality itself usually averaging anywhere from about 30 minutes to over an hour.  This is due to the large relative size of Earth over the Moon (the Moon’s diameter is only about 2150 miles), therefore casting a large umbral shadow on the Moon.  In addition, lunar eclipses are more frequent than their solar counterparts.  There are zero to three lunar eclipses per year (although possibly not all at the same location on Earth) where the Moon passes through at least a portion of the Earth’s umbral shadow (producing a partial to total eclipse).  As stated above in the solar eclipse explanation, the Moon’s orbit is tilted 5 degrees from Earth’s orbit.  For an eclipse to occur, the Moon and Earth have to be on the same orbital plane with the Sun, so the Earth’s shadow can be cast onto the Moon from the Sun.  This is why lunar eclipses only occur on average one or two times a year instead of every month.

Even though the Moon is immersed in the Earth’s umbral shadow, indirect sunlight will still reach the Moon thus illuminating it slightly.  This is because indirect sunlight reaches the Moon and also the Earth’s atmosphere will bend a very small portion of sunlight onto the Moon’s surface.  Many times during lunar totality, the color of the Moon will take on a dark red hue or brown/orange color.  As sunlight passes through Earth’s atmosphere, the blue-light is scattered out.  The amount of illumination of the Moon will vary depending on how much dust is in the Earth’s atmosphere.  The more dust present in the atmosphere, the less illuminated the Moon will be.

Lunar eclipses are safe to be viewed by the naked eye, through binoculars or a telescope.  Below is a table which shows partial and total lunar eclipses visible in the United States.

DATE OF GREATEST ECLIPSE IN CENTRAL TIME ZONE

OVERALL ECLIPSE DURATION

TOTALITY ECLIPSE DURATION

 

TIME OF GREATEST ECLIPSE

FRACTION OF MOON’S DIAMETER OBSCURED BY EARTH’S UMBRA

NOTES INVOLVING ECLIPSE 

 10/08/2014

3 hrs 20 min

 0 hrs 59 min 

5:54 AM CDT

 1.166

 All Eclipse Visible for  Western U.S.

04/04/2015

3 hrs 29 min

0 hrs 5 min

7:00 AM CDT

1.001

Eclipse ongoing at Sunrise/Moonset

09/27/2015

3 hrs 20 min

1 hr 12 min

9:47 PM CDT

1.276

All Eclipse Visible East of Rockies

01/31/2018

3 hrs 23 min

1 hr 16 min

7:30 AM CST

1.315

Eclipse ongoing at Moonset

01/20/2019

3 hrs 17 min

1 hr 02 min

11:12 PM CST

1.195

All Eclipse Visible for U.S.

05/26/2021

3 hrs 7 min

0 hrs 15 min

6:19 AM CDT

1.010

Eclipse ongoing at Sunrise/Moonset

11/19/2021

3 hrs 28 min

3:03 AM CST

0.974

Partial Eclipse ( but near total)  All Visible for U.S.

05/15/2022

3 hrs 27 min

1 hr 25 min

11:11 PM CDT

1.414

Except for Far Pacific NW, All Eclipse Visible

11/08/2022

3 hrs 40 min

1 hr 25 min

4:59 AM CST

1.359

Eclipse ongoing at Moonset for East Coast, otherwise All Eclipse Visible

09/17/2024

1 hr 03 min

9:44 PM CDT

0.085

Partial Eclipse, very little of Moon obscured

03/14/2025

3 hrs 38 min

1 hr 05 min

1:59 AM CDT

1.178

All Eclipse Visible for U.S.

03/03/2026

3 hrs 27 min

0 hrs 58 min

5:34 AM CST

1.151

Eclipse ongoing at Moonset/Sunrise for eastern U.S.

08/27/2026

3 hrs 18 min

11:13PM CDT

0.930

Partial Eclipse (but near total), All Visible for U.S.

01/11/2028

0 hrs 56 min

10:13 PM CST

0.066

Partial Eclipse, very little of Moon obscured

06/25/2029

3 hrs 40 min

1 hr 42 min

10:22 PM CDT

1.844

Eclipse ongoing at Moonrise for western U.S.

12/20/2029

3 hrs 33 min

00 hr 54 min

4:42 PM CST

1.117

Eclipse ongoing at Moonrise

 

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