A partial eclipse could result in quite a visual spectacle for viewers in the U.S. overnight on Nov. 18 and 19, 2021. According to NASA, the celestial event will be the longest partial eclipse this century, lasting more than three hours.
The Adler Planetarium in Chicago, which will be broadcasting the event starting at 1:30 a.m. Central Standard Time (CST), noted that lunar eclipses can take on a "gray, orange, or reddish color."
According to NASA, "A partial lunar eclipse is on the way, taking place overnight on November 18th and 19th, when the Moon slips into Earth's shadow for a couple of hours. Weather permitting, the eclipse will be visible from any location where the Moon appears above the horizon during the eclipse."
The eclipse will begin at 11 p.m. Pacific Standard Time (PST) for West Coast viewers, reaching a peak at 1 a.m., per NASA.
Business Insider explained that during total or near-total lunar eclipses, the moon can appear red because of refraction:
We have oxygen and nitrogen particles in Earth's atmosphere to thank for that light show. They're both better at scattering certain shorter wavelengths of light, like blue or violet, so colors with longer wavelengths like red, orange, or yellow linger. So when the moon sits in Earth's shadow, those reddish colors dominate what you see.
“Adler Skywatch: November 2021.” Adler Planetarium, 27 Oct. 2021, https://www.adlerplanetarium.org/blog/what-to-see-stargazing-tips-november-2021/.
“What’s Up: November 2021.” NASA Solar System Exploration, 2 November 2021, https://solarsystem.nasa.gov/resources/2655/whats-up-november-2021.
Woodward, Aylin. “The Longest Lunar Eclipse This Century Will Happen in 2 Weeks. Here’s How to See It.” Business Insider, 5 November 2021, https://www.businessinsider.com/how-to-see-lunar-eclipse-november-longest-in-century-2021-11.