What is a Blood Moon?


A Blood Moon occurs when the Moon, during a total lunar eclipse, appears to take on a reddish colour. This ‘blood red’ appearance happens because the Moon is illuminated by sunlight that has been filtered and refracted by the Earth’s atmosphere.

On the 27th July 2018, we will experience the longest total lunar eclipse of the 21st century. NASA lunar scientist Noah Petro of the Goddard Space Flight Centre in Maryland, USA, says that the phenomena should last between 1 hour and 43 minutes and four hours. This ‘Blood Moon’ will be visible almost everywhere in the world (with the exception of North America.) Speaking to The Independent newspaper, Dr Morgan Hollis from the Royal Astronomical Society said that the eclipse will be visible from “anywhere in the UK, weather permitting.”

Observing a lunar eclipse is much safer than viewing a solar eclipse as no special equipment is required to protect your eyes. As the Moon passes into Earth’s shadow, it will be safe to view the event with the naked eye, telescopes or binoculars.

When asked what determines how long a lunar eclipse lasted, Petro told Space.com, “What controls the duration of the lunar eclipse is the position of the Moon as it passes through the Earth’s shadow. The darkest part of Earth’s shadow is called the umbra. You can picture the umbra as a cone extending from Earth in the opposite direction to the sun. The Moon can either graze through the cone, or go right through the middle….” The nearer to the middle of the cone the Moon grazes, the longer-duration eclipse.
The Royal Astronomical Society are predicting that in the UK on 27th July, moonrise will occur at 8.49pm in London, while further north, in Glasgow, it will take place at 9.26pm. According to EarthSky.org, there will be a period of time either side of the eclipse when the Moon is travelling through the lighter part of Earth’s shadow. This transition is called the penumbra. Including that penumbral time, the eclipse will last for 3 hours and 55 minutes.

During the lunar eclipse the Moon will appear at its most ‘red’ when it lies directly in the shadow of the Earth. This brightness of colour is caused because some of the sunlight going through Earth’s atmosphere bends around the edge of Earth and falls onto the Moon’s surface.

The Blood Moon will be seen at its clearest away from cities and well lit areas. You can find a list of the very best observation spots in the UK here- https://www.independent.co.uk/travel/news-and-advice/lunar-eclipse-best-places-to-watch-uk-blood-moon-mars-explained-when-a8459956.html

If you miss this lunar eclipse, you’ll have to wait until 21st January 2019 for the next one.

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Dr Kathryn Bates is a graduate of archaeology and history. She has excavated across the world as an archaeologist, and tutored medieval history at Leicester University. She joined the administrative team at Oxford Open Learning twelve years ago. Alongside her distance learning work, Dr Bates is a bestselling novelist, and an itinerant creative writing tutor for primary school children.

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