Lunar Eclipse Guide: When and How to See the Blood MoonLunar Eclipse viewing guide on what causes lunar eclipses, how to get the best views of a lunar eclipse and how to photograph a eclipse.
What is a Lunar Eclipse?
A lunar eclipse happens when the Earth comes between the Sun and the Moon and covers the Moon with its shadow. When this occurs the Moon can turn red, hence the nickname blood moon. A total lunar eclipse happens when the Earth's shadow completely covers the moon. If just a portion of the shadow falls on the moon then it is said to be a partial lunar eclipse, or if the Earth's shadow does not touch the moon, but the Earth's atmosphere does, then we call it a penumbral eclipse.
The red colour is brought about through light scattering as the Sun's rays pass through the Earth's atmosphere. The process is known as Rayleigh scattering and it bends red light from the sun like a lens into the space behind Earth. This is also why sunset and sunrise are red and orange.
The colour and magnitude of the eclipse are measured and recorded under the Danjon scale, a five-point scale useful for measuring the appearance and luminosity of the Moon during a lunar eclipse. You can find out more on the Danjon scale later in this article.
Lunar Eclipse Terms
- Umbra: The darker, central part of the Earth's shadow
- Penumbra: The lighter, outer part of the shadow cast by our planet
Viewing the Lunar Eclipse
Lunar eclipses are a few of the most easy-to-watch astronomical events. All you need is a clear view of the night sky. Your eyes are the best instrument to take in the sight. If you happen to have a pair of binoculars to hand you can use them to pan across the craters of the moon however that is simply icing on the cake.
Find an appropriate position to view the eclipse. You should be in a position to see a lunar eclipse as long as you're on the night side of the Earth when the eclipse occurs. Rural spaces with very little artificial lighting have the clearest skies and the very best viewing conditions. Urban areas, on the other hand, can give interesting backdrops in case you intend to photograph the eclipse.
Eclipse Viewing Equipment
You don't need any particular equipment for viewing a lunar eclipse, however, there are a few things that may make your lunar eclipse viewing experience even better.
- Binoculars: If you have an interest in seeing the Moon's features throughout the eclipse, binoculars are handy to have. With binoculars, you'll be able to easily see changes in the Moon's colour as the Earth's shadow moves over it. Some astronomers recommend viewing the Moon with binoculars at the start and end of totality to see a turquoise or blue band on the Moon. This band is brought about through the upper, ozone-rich part of the Earth's atmosphere filtering the red wavelengths from the sunlight, giving it a blueish colour.
- Telescope: A telescope can also be helpful if you would like to see the features of the Moon in finer detail. You can also attach your DSLR digital camera to the telescope to get a larger photograph of the eclipsed Moon.
- Camera: You do not need any particular equipment to take pictures of a lunar eclipse. A basic point-and-shoot or even a mobile phone camera can be used.
- Tripod and cable releases: To keep binoculars or cameras stable, in particular for long focal-length photographs or long exposures.
- Extra batteries: Make certain to charge all the batteries, and carry extras.
- Torch: Helps in finding your way in the dark.
The Danjon Scale for Lunar Eclipse
Danjon Scale of Lunar Eclipse Brightness is a five-point scale for measuring appearance and luminosity of the Moon during a lunar eclipse. The Danjon Scale for Lunar Eclipse was proposed by Andre-Louis Danjon when he was measuring the Earthshine on the Moon.
During a lunar eclipse, the Moon doesn't become lost against the night sky, it has a reddish or coppery hue. This is because light passing through the thin layers of the atmosphere at the edge of the Earth is refracted or bent inwards, making the Earth's shadow lighter. Our atmosphere is good at scattering blue light and the predominant colours that get through are from the red end of the spectrum.
The depth (darkness) of the eclipse is affected by many factors, such as how much cloud cover there is on the Earth and how polluted the atmosphere is. A major volcanic eruption just before a lunar eclipse can have a profound effect on the appearance of the eclipsed Moon.
The Danjon Scale is a method for measuring the depth of the eclipse. Determination of the value of depth for an eclipse is best done near mid-totality with the naked eye. The scale is subjective, and different observers may determine different values. In addition, different parts of the Moon may have different L values, depending on their distance from the centre of the Earth's umbra.
| D0 | Very dark eclipse. Moon almost invisible, especially at mid-totality. |
| D1 | Dark Eclipse, grey or brownish in colouration. Details distinguishable only with difficulty. |
| D2 | Deep red or rust-colored eclipse. Very dark central shadow, while the outer edge of the umbra is relatively bright. |
| D3 | Brick-red eclipse. Umbral shadow usually has a bright or yellow rim. |
| D4 | Very bright copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim. |
