This article originally appeared on Time.com.
The upcoming total solar eclipse, which you can watch live on TIME.combeginning at 12 p.m. ET on Monday, will cross the U.S. in less than two hours, and Americans in some states will only witness seconds of it.
The once-in-a-lifetime event on Aug. 21 will engulf parts of 14 states in sudden darkness when it moves from the West Coast diagonally down toward the East Coast. The path of totality, which starts in Oregon and ends in South Carolina, is about 70 miles wide.
It’s the first total solar eclipse with a trajectory exclusive to America, as well as the first total eclipse of the sun that will be visible from the contiguous U.S. since 1979. Total solar eclipses can be seen when the moon passes directly between the sun and the Earth and the moon completely covers the entire face of the sun.
Watch Live as the 2017 Total Solar Eclipse Crosses the U.S.
Here’s what to know about the timeframe of the August total solar eclipse:
How long is the upcoming total solar eclipse?
The total solar eclipse, which has been dubbed “The Great American Eclipse,” will last for about an hour and a half overall, but each city that catches the eclipse will only see it for a matter of minutes or seconds. The moon’s shadow travels at roughly 2,400 mph over the face of the Earth, according to Bill Kramer, a well-known expert in the eclipse chasing community.
Which cities are the first and last to see the eclipse in totality?
Skygazers in Lincoln Beach, Ore. will witness the rare event first. A partial eclipse begins there at 9:05 a.m. PST and totality starts at 10:16 a.m. The eclipse then makes its way through Idaho, Wyoming, Nebraska, Missouri, Illinois, Kentucky, Tennessee and Georgia, clipping several other states on the way. It ends near Charleston, S.C. at 2:48 p.m. EDT, just about an hour and a half after it began.
Which city will see the eclipse for the longest?
NASA says the longest duration of totality will be near Carbondale, Ill., where the sun will be completely covered for two minutes and 40 seconds. Some places, like Kansas City, Kans.— which is at the edge of totality — will only witness totality for about 20 seconds. The total solar eclipse will be visible in a hard-to-reach part of Montana for less than a minute. Here’s where you can see what the eclipse will look like for you.