What is a lunar eclipse?

What is a lunar eclipse and why do they happen? Discover the science of lunar eclipses and view amazing pictures of the rusty-red 'blood Moon'.

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Published: October 12, 2023 at 1:32 pm

A lunar eclipse occurs when the Sun, Earth and the Moon are perfectly aligned, projecting a reddish-brown tint onto the Moon that has led to it often being called a 'Blood Moon'.

Lunar eclipses are truly spectacular to behold: look up at the Moon at certain times of the year and you’ll be able to witness the motion of the Solar System on a truly grand scale.

There are three types of lunar eclipse. The most exciting of these is a total lunar eclipse. The others are a partial and penumbral lunar eclipse, which we’ll come to later.

Can't wait for the next one? Find out when the next eclipse is happening. Scroll down further to view our gallery of lunar eclipse images.

Why do lunar eclipses happen?

Mechanics of a lunar eclipse. Credit: NASA

All the lunar eclipse effects that happen, such as darkening and colour changes, are due to Earth blocking sunlight to the Moon.

Only sunlight that has been bent (refracted) by Earth’s atmosphere reaches the Moon (shown by the bent line in the diagram above).

When the Sun’s rays intercept Earth they form two zones of shadow:

  • The penumbra, where some of the Sun is always seen
  • The umbra, where the Sun is completely hidden by the Earth

The eclipse appears to begin in earnest when the Moon starts to move into this umbra region and its surface begins to darken, before turning an unusual orange-red colour.

What is a total lunar eclipse?

A total lunar eclipse captured from Mechelen in Belgium, 21 January 2019. Credit: JASPER JACOBS/AFP via Getty Images.
A total lunar eclipse captured from Mechelen in Belgium, 21 January 2019. Credit: JASPER JACOBS/AFP via Getty Images.

Total lunar eclipses can only happen at full Moon when the Sun, Earth and Moon are lined up in space.

However, most months the Moon moves above or below the Earth’s shadow, which is why eclipses don’t happen every time the Moon is full. Lunar eclipses occur when the Moon travels into the Earth’s shadow during full Moon.

Slowly, the Moon approaches the exact opposite side of the sky to where the Sun is and as it does so the Earth blocks out more and more sunlight from reaching it.

As the Moon travels into the Earth’s shadow, the left side of the Moon gradually darkens until the Moon is totally covered – totality.

Because the Sun is much bigger than the Earth, it splits our planet’s shadow into two parts: the darkest, called the umbra, and a lighter outer ring, called the penumbra.

31rd Jan 2018 Lunar Eclipse as seen from Esfahan Iran, by Kamran Janamian.
A lunar eclipse captured from Esfahan Iran, 31 January 2018. Credit: Kamran Janamian.

When the Moon is in the umbra, no direct light from the Sun reaches it, whereas in the penumbra it is partially lit by direct sunlight.

Only light that has been bent inwards by the Earth’s atmosphere can make it to the Moon when it is in the umbral shadow.

The atmosphere filters out blue light, but leaves red light, which gives the Moon a strange orange-brown colour during totality and making it a great target for astrophotography.

The phases of a total lunar eclipse, captured by Sarah and Simon Fisher, Bromsgrove, Worcestershire, 28 September 2015.
The phases of a total lunar eclipse, captured by Sarah and Simon Fisher, Bromsgrove, Worcestershire, 28 September 2015.

As the Moon goes into eclipse and dims, the sky gets darker too. You may not have realised how bright a full Moon can be.

It lights up the sky around it with a blue haze, out of which only the brighter stars are visible

During a total lunar eclipse, the darker Moon means that the fainter stars can come out and we end up with the eerie sight of a deep-red Moon surrounded by twinkling stars.

The beauty of a lunar eclipse is that it is visible wherever you are on the night-side of the Earth.

The Moon can be in shadow for over an hour and a half, so the whole thing is quite a gentle process and you won’t need any special equipment to see it.

Partial lunar eclipse

Partial lunar eclipse, Zaprudnya, Russia, 7 August 2017. Captured by Dmitry Ardashev.
Partial lunar eclipse, Zaprudnya, Russia, 7 August 2017. Captured by Dmitry Ardashev.

As for the other eclipse types: a partial eclipse is when only part of the Moon travels through the dark umbral shadow.

It can be quite noticeable though, as you can see for yourself by watching the next partial event occurring where you live.

Penumbral lunar eclipse

Penumbral Lunar Eclipse 2016, by Nikki @im_astronix, Hampshire, 16 September 2016.
Penumbral Lunar Eclipse, Hampshire, UK, 16 September 2016. Credit: Nikki @im_astronix.

You may have seen a penumbral eclipse without noticing. This is when the Moon only passes through the lighter part of the Earth’s shadow.

Sunlight still reaches the Moon, so you only see a slight dimming.

The Danjon Scale

Danjon Scale

The Danjon Scale, named after its creator, the French astronomer André-Louis Danjon, describes how dark the Moon gets during a total lunar eclipse.

It measures the darkness of an eclipse from L0 through to L4. All lunar eclipses are very different in colour, going from light orange to dark brown.

This is because during an eclipse, the Moon is only lit by light that has passed through the Earth’s atmosphere.

So the colour will depend on how much dust, volcanic ash and water vapour is in the atmosphere to affect the sunlight’s path.

The eclipse in 1884, after the huge volcanic eruption of Krakatoa, was so dark that the Moon could only just be made out, such was the amount of dust in the atmosphere.

For more info, read our guide to eclipses happening in 2023.

How to observe a lunar eclipse

Photos of lunar eclipses

A selection of some of the best images of lunar eclipses captured by BBC Sky at Night Magazine readers and astrophotographers from around the world.

For more lunar observing and imaging, read our guides on how to photograph the Moon, how to observe the Moon, and how to draw the Moon.

And don't forget to send us your images. You can also share them with us via Facebook, Twitter and Instagram.

Lunar Eclipse 15/06/2011 by Jarrod Bennett, Zaventem, Belgium. Equipment: Canon 450D
Lunar Eclipse 15/06/2011 by Jarrod Bennett, Zaventem, Belgium. Equipment: Canon 450D
Lunar Eclipse 15/06/2011 by Yann, South Africa. Equipment: Meade LX200 GPS 8 incles, Nikon D200.
Lunar Eclipse 15/06/2011 by Yann, South Africa. Equipment: Meade LX200 GPS 8 incles, Nikon D200.
Lunar Eclipse (15/06/2011) by Yann, South Africa.
Lunar Eclipse (15/06/2011) by Yann, South Africa. Equipment: LX200 GPS 8 inches, Nikon D200, Photoshop CS5.
Lunar Eclipse (15/06/2011) by Fathi Mayoof, Bahrain.
Lunar Eclipse (15/06/2011) by Fathi Mayoof, Bahrain. Equipment: Sky-Watcher 200N and Nikon D5000. Merged and processed in Photoshop.
Lunar Eclipse (10/12/2011) by Tom Howard, Sussex, UK.
Lunar Eclipse (10/12/2011) by Tom Howard, Sussex, UK. Equipment: Tripod mounted Nikon D7000 DSLR. 70-300mm Nikor lens. Kenko 1.4 Teleconverter.
Lunar Eclipse (10/12/2011) by Tim Jukes, Tsukuba, Japan.
Lunar Eclipse (10/12/2011) by Tim Jukes, Tsukuba, Japan. Equipment: Nikon D7000, Sigma 100-300mm f4 1.4x Teleconverter.
Lunar Eclipse (10/12/2011) by David Trotter, Sydney, NSW, Australia.
Lunar Eclipse (10/12/2011) by David Trotter, Sydney, NSW, Australia. Equipment: Nikon D200, 18-200mm lens, Manfrotto Tripod, 5 seconds at F5, ISO 100.
Lunar Eclipse (10/12/2011) by John O'Mahony, Sydney, Australia.
Lunar Eclipse (10/12/2011) by John O'Mahony, Sydney, Australia. Equipment: Canon 450D, Megrez 72mm refractor.
Partial Lunar Eclipse (25/04/2013) by Tom Howard, Crawley, Sussex, UK.
Partial Lunar Eclipse (25/04/2013) by Tom Howard, Crawley, Sussex, UK. Equipment: Nikon D7000 DSLR through a Skywatcher 100ED refactor on an AZ4 mount.
Lunar Eclipse (15/04/2014) by Rowland Kelly, Arthurs Creek, near Melbourne, Australia.
Lunar Eclipse (15/04/2014) by Rowland Kelly, Arthurs Creek, near Melbourne, Australia. Equipment: Olympus Camedia C760, 44 Gallon Drum.
Lunar Eclipse (28/09/2015) by José J. Chambó Bris, Vallés, Valencia, Spain.
Lunar Eclipse (28/09/2015) by José J. Chambó Bris, Vallés, Valencia, Spain. Equipment: GSO 8" @ f/3.8 & Canon EOS-100D
Lunar Eclipse (28/09/2015) by Mark Griffith, Swindon, Wiltshire, UK.
Lunar Eclipse (28/09/2015) by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Skywatcher NEQ6 pro mount & Equinox 80mm refractor & Atik 320e colour camera.
Lunar Eclipse (28/09/2015) by Alex Shute, Butser Hill, Cowplain, UK.
Lunar Eclipse (28/09/2015) by Alex Shute, Butser Hill, Cowplain, UK. Equipment: Canon EOS 1000D Modified, 135mm Canon Lens, Sky Watcher Star Adventurer.
Lunar Eclipse (28/09/2015) by Michael Britner, Parbold Nr Wigan, UK.
Lunar Eclipse (28/09/2015) by Michael Britner, Parbold Nr Wigan, UK. Equipment: Sony A300 DSLR camera, Tamron Tele-Macro lens, Tripod
Lunar Eclipse (28/09/2015) by Tom Howard, Crawley, Sussex, UK.
Lunar Eclipse (28/09/2015) by Tom Howard, Crawley, Sussex, UK. Equipment: Nikon D7000 DSLR. Meade 5000 127mm refractor. Skywatcher AZ-EQ6 mount.
Lunar Eclipse (28/09/2015) by Peter Lewis, Sutton, UK.
Lunar Eclipse (28/09/2015) by Peter Lewis, Sutton, UK. Equipment: Lumix DMC FZ72
Lunar Eclipse (28/09/2015) by Scott Phillips, Llanelli, South Wales, UK.
Lunar Eclipse (28/09/2015) by Scott Phillips, Llanelli, South Wales, UK. Equipment: Skymax 127, EQ-5, Canon 450d
Lunar Eclipse (28/09/2015) by Alan Beeston, Shropshire, UK.
Lunar Eclipse (28/09/2015) by Alan Beeston, Shropshire, UK. Equipment: Skywatcher Evostar, ED80 Ds-Pro, 0.85x FF/FR, Canon 700D, 2.5 sec Exp at 200 ISO
Lunar Eclipse (28/09/2015) by Houssem Ksontini, Tunisia.
Lunar Eclipse (28/09/2015) by Houssem Ksontini, Tunisia. Equipment: Skywatcher 150/750, NEQ3-2 mount motorised AD, Nikon D3000
Lunar Eclipse (28/09/2015) by J Robertson, Somerset, UK.
Lunar Eclipse (28/09/2015) by J Robertson, Somerset, UK. Equipment: Sony a3000 dslr, Zuiko 35mm OM2 75-150mm f4 zoom lens.
Lunar Eclipse (28/09/2015) by Stephen Charnock, Farndon, Newark, Nottinghamshire, UK.
Lunar Eclipse (28/09/2015) by Stephen Charnock, Farndon, Newark, Nottinghamshire, UK. Equipment: Canon 60D and Celestron 127EQ Newtonian (1000mm Focal Length).
Lunar Eclipse (28/09/2015) by David Saunders, Faringdon, UK.
Lunar Eclipse (28/09/2015) by David Saunders, Faringdon, UK. Equipment: Meade 8" Lx90 6.3 Focal Reducer, Canon 450D, Registx & Photoshop
Lunar Eclipse (28/09/2015) by David Saunders, Faringdon, UK.
Lunar Eclipse (28/09/2015) by David Saunders, Faringdon, UK. Equipment: Meade 8" LX90 6.3 Focal Reducer, Canon 450D, Registx & Photoshop
Lunar Eclipse (28/09/2015) by Stephen Heliczer, North London, UK.
Lunar Eclipse (28/09/2015) by Stephen Heliczer, North London, UK. Equipment: Canon EOS10, Celestron Evolution 8
Lunar Eclipse (28/09/2015) by Stephen Heliczer, North London, UK.
Lunar Eclipse (28/09/2015) by Stephen Heliczer, North London, UK. Equipment: Canon EOS10, Celestron Evolution 8, f6.2 focal reducer
Lunar Eclipse (28/09/2015) by Brendan McConnell, Cambridge, UK.
Lunar Eclipse (28/09/2015) by Brendan McConnell, Cambridge, UK. Equipment: Canon 650D, handheld, 250mm, 1/1000-1.0s exposure, ISO 200-3200, f/20-5.6
Lunar Eclipse (28/09/2015) by William Doyen, Brittany.
Lunar Eclipse (28/09/2015) by William Doyen, Brittany. Equipment: Canon EOS 600D, 200/800 mm reflector, meade lxd75 mount (lunar speed).
Lunar Eclipse (28/09/2015) by Jonas J Andersen, Silkeborg, Denmark.
Lunar Eclipse (28/09/2015) by Jonas J Andersen, Silkeborg, Denmark. Equipment: Canon 700D, Canon 55-250mm IS STM, HEQ5 Synscan.
Lunar Eclipse (28/09/2015) by Scott Phillips, Wales, UK.
Lunar Eclipse (28/09/2015) by Scott Phillips, Wales, UK. Equipment: Skywatcher Skymax 127 EQ-5, Canon 450d, Backyard EOS
Lunar Eclipse (28/09/2015) by Sarah & Simon Fisher, Bromsgrove, Worcestershire, UK.
Lunar Eclipse (28/09/2015) by Sarah & Simon Fisher, Bromsgrove, Worcestershire, UK. Equipment: Canon 600D attached to Maksutov 127mm telescope, Prime Focus single shots
Lunar Eclipse (28/09/2015) by Sarah & Simon Fisher, Bromsgrove, Worcestershire, UK.
Lunar Eclipse (28/09/2015) by Sarah & Simon Fisher, Bromsgrove, Worcestershire, UK. Equipment: Canon 600D, 300mm lens, Canon 600D attached to Maksutov 127mm telescope (Prime Focus)
Lunar Eclipse (28/09/2015) by William Doyen, Lower Normandy, France.
Lunar Eclipse (28/09/2015) by William Doyen, Lower Normandy, France. Equipment: Bresser 200/800mm Newtonian, EOS 600D
Lunar Eclipse (28/09/2015) by Ivar Kooren, Heenvliet, The Netherlands.
Lunar Eclipse (28/09/2015) by Ivar Kooren, Heenvliet, The Netherlands. Equipment: Canon 5D Mark II, 130mm APO, NEQ6, 2.5x Teleview Powermate
Lunar Eclipse (28/09/2015) by Martin Syms, Cornwall, UK.
Lunar Eclipse (28/09/2015) by Martin Syms, Cornwall, UK. Equipment: Skywatcher 8" 200p dobsonian telescope, Nikon D3200 dslr, t-ring, remote shutter.
Lunar Eclipse (28/09/2015) by Ronald Hemes, Chichester, West Sussex, UK.
Lunar Eclipse (28/09/2015) by Ronald Hemes, Chichester, West Sussex, UK. Equipment: Canon EOS 60D, 300-500mm telephoto lens, tripod, remote shutter release.
Lunar Eclipse (28/09/2015) by Mark Griffith, Swindon, Wiltshire, UK.
Lunar Eclipse (28/09/2015) by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Skywatcher NEQ6 pro mount & Equinox 80mm refractor& Atik 320e colour camera.
Lunar Eclipse (28/09/2015) by Keith Bramley, Pilling, Lancashire, UK.
Lunar Eclipse (28/09/2015) by Keith Bramley, Pilling, Lancashire, UK. Equipment: Canon 450D through MN190 scope on Backyard pier. Captured using APT.
Lunar Eclipse (28/09/2015) by David de Cuevas, Treize vents, France.
Lunar Eclipse (28/09/2015) by David de Cuevas, Treize vents, France. Equipment: Astrotech 66ED, Canon 700D, Skywatcher EQ6.
Lunar Eclipse (28/09/2015) by David de Cuevas, Treize vents, France.
Lunar Eclipse (28/09/2015) by David de Cuevas, Treize vents, France. Equipment: Astrotech 66ED, Canon 700D, Skywatcher EQ6.
Lunar Eclipse (28/09/2015) by Christian Garcia, Daganzo, Spain.
Lunar Eclipse (28/09/2015) by Christian Garcia, Daganzo, Spain. Equipment: TS 115 APO, NEQ6 Mount, Canon 5D.
Lunar Eclipse (28/09/2015) by Ralph Smyth, Lisburn, County Antrim.
Lunar Eclipse (28/09/2015) by Ralph Smyth, Lisburn, County Antrim. Equipment: SkyWatcher 80ED Refractor and Canon 1000D DSLR. All mounted on an HEQ5PRO.
Lunar Eclipse (28/09/2015) by Susan Snow, Bishops Cleeve, Cheltenham, UK.
Lunar Eclipse (28/09/2015) by Susan Snow, Bishops Cleeve, Cheltenham, UK. Equipment: Canon EOS 600D with a 300mm lens.
The Moon and the Stars by John Short, Whitburn, Tyne and Wear, UK. Equipment: Sony A7s.
The Moon and the Stars by John Short, Whitburn, Tyne and Wear, UK. Equipment: Sony A7s.
Shading into Colour by Mark Whitcutt, Newport, Wales. Equipment: Canon EOS 100D, Skywatcher Evostar 120mm refractor, RA drive
Shading into Colour by Mark Whitcutt, Newport, Wales. Equipment: Canon EOS 100D, Skywatcher Evostar 120mm refractor, RA drive
A Beauty In Earth's Shadow by Ralph Smyth, Lisburn, Co. Antrim. Equipment: Skywatcher ED80 Refractor, Canon 1000D, HEQ5PRO mount.
A Beauty In Earth's Shadow by Ralph Smyth, Lisburn, Co. Antrim. Equipment: Skywatcher ED80 Refractor, Canon 1000D, HEQ5PRO mount.
Lunar Eclipse (16/09/2016) by Nikki @im_astronix, Hampshire, UK.
Lunar Eclipse (16/09/2016) by Nikki @im_astronix, Hampshire, UK. Equipment: Canon 750D, 300mm lens, Manfrotto tripod, Shutter release cable
Lunar Eclipse (11/02/2017) by Davy Cannon, Hamilton.
Lunar Eclipse (11/02/2017) by Davy Cannon, Hamilton. Equipment: Altair Astro 102ED Triplet APO scope, Canon EOS 80D DSLR, NEQ6 Pro mount.
Lunar Eclipse (07/08/2017) by José J. Chambó, Cullera, Valencia, Spain.
Lunar Eclipse (07/08/2017) by José J. Chambó, Cullera, Valencia, Spain. Equipment: Canon EOS 100D & Tamron AF70-300
Lunar Eclipse (07/08/2017) by Dmitry Ardashev, Zaprudnya, Russia.
Lunar Eclipse (07/08/2017) by Dmitry Ardashev, Zaprudnya, Russia. Equipment: Sky-Watcher BK P2001 Newtonian reflector, HEQ5 Pro equatorial mount, ZWO ASI178MC CCD camera
Lunar Eclipse (07/08/2017) by Nikoletta Szakšly, Sümeg, Hungary.
Lunar Eclipse (07/08/2017) by Nikoletta Szakšly, Sümeg, Hungary. Equipment: Canon EOS 700D, Carl Zeiss Jena Sonnar 4/300
Lunar Eclipse (31/01/2018) by Kamran Janamian, Esfahan, Iran.
Lunar Eclipse (31/01/2018) by Kamran Janamian, Esfahan, Iran. Equipment: Canon 600 D Modified on Tripod using 70-200 L F series Lens operating on 70 mm and Astronomik UV/IR EOS clip Filter
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