The transit of Venus is not an event on the order of a regular solar eclipse, in terms of excitement or naked-eye visibility, says astronomy enthusiast Kenneth Allendoerfer.

Yet in tonight's astronomical event, he says, stargazers have an opportunity to experience a moment like those that helped shape early discoveries about the Earth itself.

"It's one of those really rare events that historically was one of the ways that the old astronomers used to measure the size of the solar system," Allendoerfer says.

In the time before such education was formalized, he says, scientists were dependent upon the work of royal societies and "gentleman scientists" to collect and catalogue the data upon which broader conclusions were reached. 

"It would have been something Thomas Jefferson would have done had he been alive at the time," Allendoerfer says. "An event like this was fairly significant scientifically because they would be able to do all kinds of calculations."

The transit of Venus—in which the orbital path of the planet passes between the Earth and Sun—only happens every 105 years or so, he says, "but when it does occur, there are two of them right in a row." For most of us, this will be our last shot this lifetime, as the next transit of Venus isn't due until 2117.

To the naked eye, Venus will only appear as a small black speck on the surface of the sun, Allendoerfer says. As with any attempted solar gazing, it's important that viewers take precautions to protect their eyes and do not attempt to stare directly at the sun without special lenses.

A simple pinhole projector can be constructed by covering a paper towel tube with aluminum foil and poking holes in the end to project the image on a larger viewing field, like a piece of poster board or a bedsheet.

"You shouldn't go up there with your binoculars or even your heavy sunglasses," he says.

Allendoerfer, an engineering research psychologist who works at the Federal Aviation Administration research and development facility at the Atlantic City airport, describes himself as an "enthusiastic amateur astronomer."

His guided demonstration on the transit of Venus—tonight at the Knight Park pavilion around 6 p.m.—is intended to be the first gathering of the "Collings Lab" community, an informal organization he's leading to bring community science to kids in town. All the details aren't worked out just yet, but Allendoerfer is hoping that Collings Lab could provide equipment-sharing and guided expertise that can help broaden the interests of young people in the sciences.

Can't make it out? You can watch the transit of Venus online:

• The Slooh Space Camera will offer an 8-hour webcast of the transit that includes real-time video feeds from 10 telescopes around the world.
• Astronomers Without Borders will carry a video stream of the transit from the Mount Wilson Observatory in California.
• NASA will offer a live video feed from Mauna Kea observatory in Hawaii with expert commentary.
• The San Francisco Exploratorium will host an online video stream from the Mauna Loa telescope in Hawaii.
• Don Pettit, an astronaut currently aboard the International Space Station, will become the first person to ever photograph a transit of Venus from outer space.

David Powell contributed to this report.