Last week, North America was treated to the unusual sight of an X on the Moon. On Thursday, viewers in North America will be able to witness a relatively rare event, occurring roughly once every two and half years, as the Moon turns a blood-red color in the night sky.
While you would be forgiven in days gone by for assuming that the red color was a sign of impending doom, the color is the result of a total lunar eclipse, resulting in a “Blood Moon”. On Thursday, as the Earth comes between the Sun and the Moon, our planet will block out most of the sunlight reaching the Moon. Unlike solar eclipses, which last minutes, the lunar eclipse will last up to an hour.
So why the red color, rather than the Moon simply being covered in shadow? That is down to a phenomenon known as Rayleigh scattering. When the Sun’s light hits our atmosphere, light in the blue spectrum is scattered more efficiently than red light by particles within it, called Rayleigh scattering. With less blue light hitting your eyes, you will perceive the Sun as tinted slightly yellow. The more atmosphere the light has to travel through – say at sunrise and sunset – the more blue light gets scattered, making the Sun appear yellower or red. Conversely, when the Sun is directly above you, it will appear whiter, as the blue light has less atmosphere to scatter through in order to reach your eyes.
During a lunar eclipse, the only light that falls on the Moon (discounting starshine) is light that has passed through the Earth’s atmosphere. As blue light is more easily scattered, while red light takes a more direct route, the result is that the Moon is bathed in an eerie, blood-red glow.
“The more dust or clouds in Earth’s atmosphere during the eclipse, the redder the Moon will appear,” NASA explains. “It’s as if all the world’s sunrises and sunsets are projected onto the Moon.”
How the Moon turns red during a lunar eclipse.
Image credit: NASA Goddard Space Flight Center/Scientific Visualization Studio
Unlike solar eclipses, there is no need for any specialist equipment to view the lunar eclipse, though you may choose to use binoculars or a telescope. However, viewers in North America will need to stay up pretty late if they want to see totality – when the Moon is completely covered in shadow. This happens at around 06:26 am UTC, or 11:26 pm PDT and 2:26 am EDT, according to NASA.
“That totality will last for close to an hour, so even if it’s cloudy you may still be able to glimpse it if the clouds are scattered,” Dr Renee Weber, chief scientist at NASA’s Marshall Space Flight Center in Huntsville, Alabama, said in a statement.
“As a child I remember begging my mom to wake me up to see a lunar eclipse,” Weber added. “The next morning I was mad because she didn’t wake me up – except she DID, but because I was so sleepy I don’t have any memories of it! Fortunately I’ve gotten a few chances to see lunar eclipses as an adult, including the one that occurred on Jan. 20, 2019, which I also photographed.”
As long as you can get a clear view of the sky, you should be able to see it in North and South America. Only the initial part of the eclipse will be viewable from Europe and Africa, before the Moon sets. But people in Europe, Africa, Asia, and Australia will not have to wait long for a good look at a Blood Moon, with the next total lunar eclipse taking place on September 7.
