On Thursday and Friday, skywatchers will get to experience a nearly total lunar eclipse—but what you see will depend on where in the world you live.
The partial lunar eclipse— which NASA described as "almost total"—will be the longest for a century, lasting 3 hours, 28 minutes, and 23 seconds.
NASA explains on its website why this is an almost total eclipse: "A lunar eclipse occurs when the Sun, Earth, and Moon align so that the Moon passes into Earth's shadow.
"In a total lunar eclipse, the entire Moon falls within the darkest part of Earth's shadow, called the umbra. In this eclipse, up to 99.1 percent of the Moon's disk will be within Earth's umbra."
During the eclipse, just a tiny sliver of the moon will be visible, with the vast majority disappearing into Earth's shadow as the sun and moon pass opposite sides of the planet.
The eclipse will be in various regions of the globe, including North America, eastern Australia, New Zealand, and Japan. The best view of the eclipse will be at its peak which will occur at 4:03 AM EDT on November 19th.
NASA also gives a timeline of how the eclipse will proceed and what will be seen where.
At 1:02 a.m. EDT, the moon enters the Earth's penumbra, the outer part of our planet's shadow. The moon will begin to dim at this point, but the effect will be subtle.
By 3:45 a.m. EDT the moon will have slipped further into earth's shadow so that 95 percent of its disc is in the umbra. At this point, it will take on a reddish-brown hue, best seen with binoculars or a telescope.
This red coloration will be best seen at 4:03 a.m. EDT, when the eclipse is at its peak. At this point, the partial eclipse will be visible across all of North America, as well as large parts of South America, Polynesia, eastern Australia and northeastern Asia.
The red coloration will disappear at around 4:20 a.m. as the moon moves out of Earth's shadow. By 7:04 a.m. EDT the eclipse will be over.
"For U.S. East Coast observers, the partial eclipse begins a little after 2 a.m., reaching its maximum at 4 in the morning," NASA reported. "For observers on the West Coast, that translates to beginning just after 11 p.m., with a maximum at 1 a.m."
As mentioned above, as the moon slips into the shadow of Earth it will take on a reddish-brown color. This is because of how photons interact will atoms in Earth's atmosphere.
Photons of red light, with their longwave length and low frequency, normally pass unhindered through the Earth's atmosphere. Photons of blue light, on the other hand, have a shorter wavelength and higher frequency.
This means blue photons are scattered by interactions with atoms in the atmosphere. This process, called Rayleigh scattering, is the reason the sky is blue, as photons of blue light bounce around the sky before they hit your eye.
This changes when the sun is setting because the red photons now have a lot more atmosphere to travel through. This means they are forced to interact with more atoms in the atmosphere, and therefore have a greater chance of scattering before they reach our eyes.
The reason the moon turns red during an eclipse is light from the sun has to pass through Earth's atmosphere before it reaches, and is reflected from the lunar surface.
Just how red the moon will appear depends on how many clouds and how much dust there is in Earth's atmosphere at the time of the eclipse. More dust and clouds, more Rayleigh scattering, and the redder the moon will appear.
