The longest partial lunar eclipse of the century will get underway late Thursday for the Bay Area and will stick around well into the wee hours of Friday morning.
The near-total eclipse, in which the full moon will fit almost fully into the Earth’s shadow and create a dramatic visual effect, is expected to arrive at 11:19 p.m. PST and will last for 3 hours, 28 minutes and 23 seconds, making it the longest lunar eclipse of the century, according to statistics compiled by NASA. The longest total eclipse this century occurred on July 27, 2018, and lasted 1 hour, 42 minutes and 57 seconds.
It’s also the longest partial lunar eclipse in nearly six centuries, according to NASA’s data. The last time a longer partial lunar eclipse occurred was Feb. 18, 1440, at 3 hours, 28 minutes and 46 seconds — and the next one won’t be until Feb. 8, 2669, predicted to be 3 hours, 30 minutes and 2 seconds.
And why is this event unusually long? According to timeanddate.com, it’s because the eclipse’s maximum point will occur as the moon nears its farthest point from Earth, known as its apogee. The greater the distance, the more time it takes the moon to pass through the Earth’s shadow.
At its maximum effect, around 1 a.m. PST Friday, 97% of the moon’s face will be covered in shadow, turning it a deep red, according to the website space.com. Only a little sliver of the moon will shine, NASA says.
The eclipse will be visible across much of the globe, including the Bay Area — but only if the weather cooperates with a clear sky. And unfortunately, experts say that’s not likely.
“Right now it is not looking so good,” said Matt Mahle, meteorologist with the National Weather Service. The long-range forecast is for a low pressure system to move across Northern California just in time for the eclipse.
“Clouds are forecast with a low-end chance of showers Thursday night,” Mahle said.
If you can’t watch the event in person, live coverage is offered by the Virtual Telescope Project and by timeanddate.com.
Sam Whiting is a San Francisco Chronicle staff writer. Email: swhiting@sfchronicle.com. Twitter:@samwhitingsf