Passing Into Earth's Shadow

Lunar eclipses occur when the Sun, Earth and the Moon are aligned (called a "syzygy") and the Moon moves into Earth’s shadow during the Full Moon phase of its orbit. This causes the Moon to darken and often turn ‘blood red’ if some sunlight reaches the Moon after passing through Earth’s dirty atmosphere! Viewing a lunar eclipse is an interesting astronomical event for young amateur astronomers!









What Is A Lunar Eclipse?!

A lunar eclipse occurs when part, or the entire, Moon passes into Earth’s shadow which is divided into two parts, the partial shadow region known as the penumbra and the central full shadow region known as the umbra.

There are three main types of lunar eclipse;

  • A penumbral eclipse is where the moon only enters Earth’s penumbra.
  • A partial lunar eclipse occurs when only a portion of the moon enters the umbra.
  • A total lunar eclipse is observed when the moon travels completely into the umbra.

An eclipse may last up to 4 hours (from start to finish) with the Moon being totally eclipsed as much as 107 minutes! However, even when it is totally eclipsed the Moon is still dimly visible as Earth’s atmosphere refracts some sunlight into the Earth’s shadow which gives the Moon a reddish-brown appearance.

Total lunar eclipses are much more interesting than partial eclipses, partly because of the appearance of a full moon turning reddish-brown (referred to as a “Blood Moon”), but also because some are much darker than others. This is due to the varying transparency of Earth’s atmosphere (i.e. whether the horizon is over the dusty deserts or clean oceans).

Where And When Do They Occur?!

To witness a lunar eclipse you don’t need to be at a specific point on the globe (unlike when viewing a total Solar Eclipse), you just need to be able to see the Full Moon (between dusk to dawn during the night) when the eclipse is occurring. This means that lunar eclipses are visible from about half the Earth’s surface!

Partial lunar eclipses occur at least twice a year (a maximum of 5 in one year is possible). Total lunar eclipses occur far less frequently, on average once a year.

You won’t need to stare at the Moon night after night, just waiting for an eclipse either as Astronomers are really good at predicting the time and place of lunar eclipses for hundreds of years into the future!

A special event which occurs during a total lunar eclipse, called a selenelion, is where both the Sun and the eclipsed Moon (which is in Earth’s umbra) can be observed at the same time! This only happens just before sunset or just after sunrise (for between 2-5 minutes) when both bodies appear just above the horizon at nearly opposite points in the sky. Although this should be impossible, the Sun and the eclipsed Moon can both be seen at the same time because the refraction of light through the Earth’s atmosphere causes each of them to appear higher in the sky than their true geometric position.

If There’s A Full Moon Each Month Why Don’t Lunar Eclipses Occur Every Month?

Despite the Moon completing an orbit of the Earth every month, lunar eclipses only occur a couple times of year because the Moon orbits the Earth at an angle of 5 degrees. This means the alignment during the full moon phase isn’t always perfect enough for the Moon to pass through Earth’s shadow. We need to wait until the Moons angled orbit lines up directly with the Sun and Earth!

Future Total Lunar Eclipses To Look Forward Too Before The Year 2030!!

  • July 27th 2018,              duration = 1hr 43m, best viewed from Africa, Europe, Asia.
  • January 21st 2019,       duration = 1hr 02m, best viewed from Pacific, Americas, Europe, Africa.
  • May 26th 2021,              duration = 0hr 15m, best viewed from East Asia, Australia, Pacific, Americas.
  • May 16th 2022,              duration = 1hr 25m, best viewed from Americas Europe, Africa.
  • November 8th 2022,   duration = 1hr 25m, best viewed from Asia, Australia, Pacific, Americas.
  • March 14th 2025,         duration = 1hr 05m, best viewed from Pacific, Americas, West Europe, West Africa.
  • September 7th 2025,   duration = 1hr 22m, best viewed from Europe, Africa, Asia, Australia.
  • March 3rd 2026,           duration = 0hr 58m, best viewed from East Asia, Australia, Pacific, Americas.
  • December 31st 2028,  duration = 1hr 11m, best viewed from Europe, Africa, Asia, Australia, Pacific.
  • June 26th 2029,            duration = 1hr 42m, best viewed from Americas, Europe, Africa, Mid East.
  • December 20th 2029, duration = 0hr 54m, best viewed from Americas, Europe, Africa, Asia.

And remember, unlike solar eclipses, you don’t need special eclipse glasses to view a total lunar eclipse!

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Geometry of a Lunar Eclipse