Blood Moon 2018: Astronomy expert’s guide and top tips for Friday’s lunar eclipse
PUBLISHED: 12:29 26 July 2018 | UPDATED: 13:47 26 July 2018
A doctor at Hatfield’s University of Hertfordshire has given an expert’s guide to the ‘Blood Moon’ ahead of this Friday’s lunar eclipse.
The Moon will pass through the Earth’s shadow at 8.30pm, which will darken the Moon and turn it a reddish colour.
But what actually happens? What should we look out for? Is the world going to end? Thankfully, the university’s Dr Samantha Rolfe has bestowed us with her wisdom.
What is an eclipse?
•A total eclipse of the Moon occurs because the orbits of the Sun, Earth and Moon align such that the Moon moves directly into the shadow of the Earth.
•Unlike a solar eclipse where the Moon blocks out the disc of the Sun, we can still see the surface of the Moon during a total lunar eclipse.
•This seems like it wouldn’t be possible, as the Earth is blocking the light from the Sun, but during totality light from the Sun is scattered through the Earth’s atmosphere and still reaches the surface of the Moon, an effect known as Rayleigh Scattering.
But why is it red?
•The effect that causes the red colour of the Moon during a total lunar eclipse is called Raleigh Scattering.
•Rayleigh Scattering occurs when light from the Sun interacts with the molecules in the atmosphere. The energy and wavelength of the light doesn’t change but the direction it is travelling in can.
•Blue light has a shorter wavelength and is scattered more effectively, so when the Moon is in the shadow of the Earth during an eclipse, the blue light is scattered away, but the longer wavelength red light coming from the Sun is not.
•This light reaches the surface of the Moon, which reflects back towards the Earth and makes the surface appear red.
My head hurts! What should I expect? Werewolfs?
•You may not see the Moon from the moment it rises depending on what objects are on your eastern horizon.
•The Moon will eventually rise above any objects in your view and you will still be able to see the ‘Blood Moon’ as the point of greatest totality (GT) occurs at 9.21pm.
•Totality continues until 10.13pm. Totality is when the Moon is in the full shadow of the Earth – the ‘umbra’ (Latin for ‘shadow’).
•The Moon will remain in the partial shadow of the Earth, the ‘penumbra’ (pen, from the Latin for ‘almost, nearly’) until after midnight at 12.28am, so there is plenty of time to see different parts of the eclipse.
•This eclipse is extra special as the Moon is in totality for 103 minutes, the longest that will occur in the 21st century.
•Furthermore, it is a ‘Micro Moon’, where the Moon is furthest from the Earth in its orbit (apogee), appearing approximately six per cent smaller than an average full Moon.
•If possible find a good eastern horizon, free of trees and buildings.
•Pack a folding chair or blanket, a light jacket (despite the warm weather the evening will feel a lot cooler especially if you are on exposed or higher ground), and some snacks (who doesn’t want to snack while watching an astronomical phenomenon), a camera and friends and family.
•One more thing: fingers crossed for clear skies.