Introduction

What is an eclipse of the Moon? What causes eclipses and why? How often do eclipses happen and when is the next eclipse of the Moon? You'll learn the answers to these questions and more in MrEclipse's primer on lunar eclipses.

The Moon is a cold, rocky body about 2,160 miles (3,476 km) in diameter. It has no light of its own but shines by sunlight reflected from its surface. The Moon orbits Earth about once every 29 and a half days. As it circles our planet, the changing position of the Moon with respect to the Sun causes our natural satellite to cycle through a series of phases:

• New Moon > New Crescent > First Quarter > Waxing Gibbous> Full Moon >
  Waning Gibbous > Last Quarter > Old Crescent > New Moon (again)

Phases of the Moon.

The phase known as New Moon can not actually be seen because the illuminated side of the Moon is then pointed away from Earth. The rest of the phases are familiar to all of us as the Moon cycles through them month after month. Did you realize that the word month is derived from the Moon's 29.5 day period?

Many early civilizations used the Moon's monthly cycle to measure the passage of time. In fact, some calendars are synchronized to the phases of the Moon. The Hebrew, Muslim and Chinese calendars are all lunar calendars. The New Moon phase is uniquely recognized as the beginning of each calendar month just as it is the beginning on the Moon's monthly cycle. In comparison, the Full Moon phase occurs mid-way through the lunar month.

The Full Moon is popularly known as the phase of love and romance. When the Moon is Full, it rises at sunset and is visible all night long. At the end of the night, the Full Moon sets just as the Sun rises. None of the Moon's other phases have this unique characteristic. It happens because the Moon is directly opposite the Sun in the sky when the Moon is Full. Full Moon also has special significance with regard to eclipses.

Geometry of the Sun, Earth and Moon During an Eclipse of the Moon
Earth's two shadows are the penumbra and the umbra.
(Sizes and distances not to scale)

Types of Lunar Eclipses

An eclipse of the Moon (or lunar eclipse) can only occur at Full Moon, and only if the Moon passes through some portion of Earth's shadow. That shadow is actually composed of two cone-shaped components, one nested inside the other. The outer or penumbral shadow is a zone where the Earth blocks part but not all of the Sun's rays from reaching the Moon. In contrast, the inner or umbral shadow is a region where the Earth blocks all direct sunlight from reaching the Moon.

Astronomers recognize three basic types of lunar eclipses:

1. Penumbral Lunar Eclipse

• The Moon passes through Earth's penumbral shadow.
• These events are of only academic interest because they are subtle and hard to observe.
(click for photo example)

2. Partial Lunar Eclipse

• A portion of the Moon passes through Earth's umbral shadow.
• These events are easy to see, even with the unaided eye.
(click for photo example)

3. Total Lunar Eclipse

• The entire Moon passes through Earth's umbral shadow.
• These events are quite striking due to the Moon's vibrant red color during the total phase (totality).
(click for photo example)

Now you might be wondering "If the Moon orbits Earth every 29.5 days and lunar eclipses only occur at Full Moon, then why don't we have an eclipse once a month during Full Moon?". I'm glad you asked! You see, the Moon's orbit around Earth is actually tipped about 5 degrees to Earth's orbit around the Sun. This means that the Moon spends most of the time either above or below the plane of Earth's orbit. And the plane of Earth's orbit around the Sun is important because Earth's shadows lie exactly in the same plane. During Full Moon, our natural satellite usually passes above or below Earth's shadows and misses them entirely. No eclipse takes place. But two to four times each year, the Moon passes through some portion of the Earth's penumbral or umbral shadows and one of the above three types of eclipses occurs.

When an eclipse of the Moon takes place, everyone on the night side of Earth can see it. About 35% of all eclipses are of the penumbral type which are very difficult to detect, even with a telescope. Another 30% are partial eclipses which are easy to see with the unaided eye. The final 35% or so are total eclipses, and these are quite extrordinary events to behold.

What is the difference between a lunar eclipse and a solar eclipse? A solar eclipse is an eclipse of the Sun. It happens when the Moon passes between the Earth and the Sun. This is only possible when the Moon is in the New Moon phase. For more information, see Solar Eclipses for Beginners.

Total Lunar Eclipse of 2004 Oct 27-28
Beginning (right), middle (center) and end (left) of totality
(click to see photo gallery)

Why is the Moon Red During a Total Lunar Eclipse?

During a total lunar eclipse, the Earth blocks the Sun's light from reaching the Moon. Astronauts on the Moon would then see the Earth completely eclipse the Sun. (They would see a bright red ring around the Earth as they watched all the sunrises and sunsets happening simultaneousely around the world!) While the Moon remains completely within Earth's umbral shadow, indirect sunlight still manages to reach and illuminate it. However, this sunlight must first pass deep through the Earth's atmosphere which filters out most of the blue colored light. The remaining light is a deep red or orange in color and is much dimmer than pure white sunlight. Earth's atmosphere also bends or refracts some of this light so that a small fraction of it can reach and illuminate the Moon.

The total phase of a lunar eclipse is so interesting and beautiful precisely because of the filtering and refracting effect of Earth's atmosphere. If the Earth had no atmosphere, then the Moon would be completely black during a total eclipse. Instead, the Moon can take on a range of colors from dark brown and red to bright orange and yellow. The exact appearance depends on how much dust and clouds are present in Earth's atmosphere. Total eclipses tend to be very dark after major volcanic eruptions since these events dump large amounts of volcanic ash into Earth's atmosphere. During the total lunar eclipse of December 1992, dust from Mount Pinatubo rendered the Moon nearly invisible.

All total eclipses start with a penumbral followed by a partial eclipse, and end with a partial followed by a penumbral eclipse (the total eclipse is sandwiched in the middle). The penumbral phases of the eclipse are quite difficult to see, even with a telescope. However, partial and total eclipses are easy to observe, even with the naked eye.

Total Lunar Eclipse of 2000 Jan 20-21
Beginning (right), middle (center) and end (left) of totality
(click to see more photos)

Observing Lunar Eclipses

Unlike solar eclipses, lunar eclipses are completely safe to watch. You don't need any kind of protective filters. It isn't even necessary to use a telescope. You can watch the lunar eclipse with nothing more than your own two eyes. If you have a pair of binoculars, they will help magnify the view and will make the red coloration brighter and easier to see. A standard pair of 7x35 or 7x50 binoculars work fine. Remember to dress warmly and enjoy the spectacle!

Amateur astronomers can actually make some useful observations during total eclipses. It's impossible to predict exactly how dark the Moon will appear during totality. The color can also vary from dark gray or brown, through a range of shades of red and bright orange. The color and brightness depend on the amount of dust in Earth's atmosphere during the eclipse. Using the Danjon Brightness Scale for lunar eclipses, amateurs can categorize the Moon's color and brightness during totality.

Another useful amateur activity requires a telescope. Using a standard list lunar craters, one can careful measure the exact time when each crater enters and leaves the umbral shadow. These crater timings can be used to estimate the enlargement of Earth's atmosphere due to airborne dust and volcanic ash.

Of course, an eclipse of the Moon also presents a tempting target to photograph. Fortunately, lunar eclipse photography is easy provided that you have the right equipment and use it correctly. See MrEclipse's Picks for camera, lens and tripod recommendations. For more photographs taken during previous lunar eclipses, be sure to visit Lunar Eclipse Photo Gallery.

Lunar Eclipse Frequency and Future Eclipses

Penumbral eclipses are of little interest because they are hard to see. If we consider only partial and total lunar eclipses, how often do they occur?

During the five thousand year period from 2000 BCE through 3000 CE, there are 7,718 eclipses of the Moon (partial and total). This averages out to about one and a half eclipses each year. Actually, the number of lunar eclipses in a single year can range from 0 to 3. The last time that 3 total lunar eclipses occurred in one calendar year was in 1982. Partial eclipses slightly outnumber total eclipses by 7 to 6.

The table below lists every lunar eclipse from 2024 through 2034. Click on the eclipse Date to see a diagram of the eclipse and a world map showing where it is visible from. Although penumbral lunar eclipses are included in this list, they are usually hard to see because they are faint.

The second column TD of Greatest Eclipse is the Terrestrial Dynamical Time of greatest eclipse. The Umbral Magnitude is the fraction on the Moon's diameter immersed in the umbra at maximum eclipse. For magnitudes greater than 1.0, the eclipse is total. For negative values, it is a penumbral eclipse. The Eclipse Duration is the duration of the partial phases as well as the total phase (in bold; total eclipses only). The Geographic Region of Eclipse Visibility offers a brief description of where an eclipse can be seen. Although penumbral lunar eclipses are included in this list, they are usually hard to see because they are faint.

Lunar Eclipses: 2024 - 2034
Calendar Date	TD of Greatest Eclipse	Eclipse Type	Saros Series	Umbral Magnitude	Eclipse Duration	Geographic Region of Eclipse Visibility
2024 Mar 25	07:13:59	Penumbral	113	-0.132	-	Americas
2024 Sep 18	02:45:25	Partial	118	0.085	01h03m	Americas, Europe, Africa
2025 Mar 14	06:59:56	Total	123	1.178	03h38m 01h05m	Pacific, Americas, w Europe, w Africa
2025 Sep 07	18:12:58	Total	128	1.362	03h29m 01h22m	Europe, Africa, Asia, Australia
2026 Mar 03	11:34:52	Total	133	1.151	03h27m 00h58m	e Asia, Australia, Pacific, Americas
2026 Aug 28	04:14:04	Partial	138	0.930	03h18m	e Pacific, Americas, Europe, Africa
2027 Feb 20	23:14:06	Penumbral	143	-0.057	-	Americas, Europe, Africa, Asia
2027 Jul 18	16:04:09	Penumbral	110	-1.068	-	e Africa, Asia, Australia, Pacific
2027 Aug 17	07:14:59	Penumbral	148	-0.525	-	Pacific, Americas
2028 Jan 12	04:14:13	Partial	115	0.066	00h56m	Americas, Europe, Africa
2028 Jul 06	18:20:57	Partial	120	0.389	02h21m	Europe, Africa, Asia, Australia
2028 Dec 31	16:53:15	Total	125	1.246	03h29m 01h11m	Europe, Africa, Asia, Australia, Pacific
2029 Jun 26	03:23:22	Total	130	1.844	03h40m 01h42m	Americas, Europe, Africa, Mid East
2029 Dec 20	22:43:12	Total	135	1.117	03h33m 00h54m	Americas, Europe, Africa, Asia
2030 Jun 15	18:34:34	Partial	140	0.502	02h24m	Europe, Africa, Asia, Australia
2030 Dec 09	22:28:51	Penumbral	145	-0.163	-	Americas, Europe, Africa, Asia
2031 May 07	03:52:01	Penumbral	112	-0.090	-	Americas, Europe, Africa
2031 Jun 05	11:45:17	Penumbral	150	-0.820	-	East Indies, Australia, Pacific
2031 Oct 30	07:46:44	Penumbral	117	-0.320	-	Americas
2032 Apr 25	15:14:51	Total	122	1.191	03h31m 01h06m	eastern Africa, Asia, Australia, Pacific
2032 Oct 18	19:03:40	Total	127	1.103	03h16m 00h47m	Africa, Europe, Asia, Australia
2033 Apr 14	19:13:51	Total	132	1.094	03h35m 00h49m	Europe, Africa, Asia, Australia
2033 Oct 08	10:56:23	Total	137	1.350	03h22m 01h19m	Asia, Australia, Pacific, Americas
2034 Apr 03	19:06:60	Penumbral	142	-0.227	-	Europe, Africa, Asia, Australia
2034 Sep 28	02:47:37	Partial	147	0.014	00h27m	Americas, Europe, Africa

Geographic abreviations (used above): n = north, s = south, e = east, w = west, c = central

For an extended version of this table, see: Lunar Eclipse Preview: 2021-2040.

Recent total lunar eclipses visible from the USA include the eclipses on Aug. 28, 2007, Feb. 21, 2008, Dec. 21, 2010, Apr. 15, 2014, Oct. 08, 2014, Apr. 04, 2015, Sep. 28, 2015, Sep. 28, 2015, Sep. 28, 2015, Jan, 31, 2018 , Jan. 20/21, 2019, May 26, 2021 , May 16, 2022 , and Nov 08, 2022 .

Upcoming lunar eclipses visible from the USA include Mar 14, 2025 , Mar 03, 2026 , and Jun 26, 2029 .

Eclipse Publications

The five volumes of the Eclipse Almanac publication series include maps and diagrams of every solar and lunar eclipse from 2021 to 2070 (each volume covers a single decade). Each vomume available in Black & White, Color, and Kindle editions.