Today, July 16, 2019, marks 50 years to the day since Apollo 11 blasted off from Earth on its mission to put humans on the Moon for the first time. As if the Moon is letting us know it's still thinking about us after all these years, parts of planet Earth will be graced with a partial lunar eclipse tonight.
The partial lunar eclipse will visible in the UK after sunset at approximately 22:30 BST, according to the Royal Astronomical Society. The skies are forecasted to remain clear of clouds throughout the evening, so about 60 percent of the visible lunar surface will turn a rusty red or grey color around this time.
The spectacle will also be visible across a large part of Asia, all of Africa, eastern parts of South America, and the western part of Australia. Unfortunately, the US and the rest of North America won’t be able to experience the lunar eclipse. However, if you're still interested, the Virtual Telescope Project will share a live stream of the lunar eclipse as it presents itself above the skyline of Rome.
In the UK, the Moon will hang low in the sky throughout the eclipse, so you'll need an unobstructed south-eastern and southern horizon to view it. Unlike a solar eclipse, it's completely safe to observe with the naked eye as the light is not too intense.
Lunar eclipses occur when the Earth, Sun, and Moon are almost exactly in line, with the Earth placed in between the Sun and Moon (as you can see above). The shadow of the Earth is cast on the Moon, obscuring a noticeable amount of sunlight from reaching the lunar surface.
As this occurs, the moon will appear to turn a rusty red or orange color. The effect is known as Rayleigh scattering, when gas and other small particles in Earth's atmosphere cause the shorter wavelengths of light, like indigo and blue, to scatter. During the day, this results in the sky appearing blue. However, if light travels through enough atmosphere, so much light will be scattered that only longer wavelengths, like red or orange, will remain. This is the effect we see during sunrise or sunset on Earth, and it's also what you see during a lunar eclipse.