In case you haven't already heard, there is going to be a total eclipse of the sun on Aug. 21, and it is going to be a huge event because for the first time in nearly 100 years, the shadow will cross the United States from coast-to-coast.

During a total solar eclipse, the moon passes completely in front of the sun, blocking out all light except for the glow of the corona, or the sun's outer atmosphere. Depending on where you are in the U.S., you will see 50 to 100 percent total darkness, or totality.

The Quad-Cities will see 91.46 percent totality at about 1:14 p.m., with the eclipse beginning at about 11:48 a.m. and continuing to about 2:38 p.m., Jeff Struve, president of the Quad-Cities Astronomical Society, said. If it is a clear day, the effect will be an "eerie" cloudiness, he said.

People who follow astronomy made motel reservations for regions of "totality" more than a year ago, and libraries all over the country, including those in the Quad-Cities, have ordered stocks of special glasses so that patrons can safely view the eclipse at viewing parties. (A person should never look directly at the sun with the naked eye even during a partial eclipse because that could cause permanent damage.)

The Putnam Museum, Davenport, is hosting a free, special event in cooperation with the Quad-Cities Astronomical Society in which people can watch the total eclipse on the big screen as it is broadcast live from a site in Nebraska.

Robert Mitchell, a professor of engineering and physics at St. Ambrose University and a member of the society, will do the broadcast from Aurora, Nebraska, which is on the path of totality. He will use special filters so that the broadcast will be safe for people in the theater to watch, beginning at 11:30 a.m. and continuing until 1:30 p.m.

Accompanying him will be several other Quad-Citians, including Struve, who will provide live commentary. And society member Dale Hendricks will be in the Putnam, answering questions during the broadcast.

Other relatively nearby areas of totality will be in Missouri and southern Illinois, but Mitchell and the others decided on Nebraska because the chances are better of clear skies. And weather forecasting has a better probability of being accurate in that part of the country.

Weather is important because in the event of heavy clouds or rain, there will be little to see except that the sky will seem a little darker. That's not what they want.

So, if at 5 p.m. Aug. 20, the Nebraska forecast calls for cloudy skies on Aug. 21, the group will hop into their cars and drive to another location.

"We will go as far west as we need to go," Mitchell said. But he's well aware that if he decides to get on the road, so will thousands of other people.

"I've been to workshops (on the eclipse) where they were predicting horrible traffic conditions," Paul Levesque, a society member from Moline, said.

The group would have to change their plans based on the forecast rather than real-time conditions because real-time would be too late.

"You can't chase the eclipse," Levesque said. "It's traveling hundreds of miles per hour. It's traveling faster than the speed of sound."

On the day of the eclipse, "some people are predicting Facebook is going to explode," Mitchell said. He has heard of organizations that are trying to collect videos from people along the route with the intent of stitching them together in one big movie. 

Although the eclipse is still a month away, Struve, who is helping with the broadcast to the Putnam, "is on pins and needles."

"What if it doesn't work?" he said. "You only get one chance. What if we lose the network or if our computer doesn't boot up? All you can do is prepare as much as you can and then let it run and enjoy yourself."

In Moline, members of the Popular Astronomy Club will be at the public library with a mobile observatory equipped to directly observe the sun, part of a viewing party from 11 a.m. to 3 p.m.