What: Transit of Venus program
Where: Tellus Science Museum, 100 Tellus Drive, Cartersville, Ga.
When: 6-9 p.m. tonight
Cost: $12 adults, $10 seniors, $8 children and students with ID, free to active military with ID
Astronomer David Dundee is offering a deal for those who visit the Tellus Science Museum tonight in Cartersville, Ga., for a special program dedicated to the transit of Venus.
Those who save their receipt will get in free next time the Earth, Venus and sun line up perfectly so skywatchers can see Venus as a little black disc passing in front of the sun.
"They can use that receipt for the next transit of Venus," Dundee said tongue-in-cheek, since the celestial event won't take place again for 105 years.
"If you miss it this time, you're out of luck until 2117," he said.
The Tellus Science Museum, which is next to Interstate 75 about an hour's drive from Chattanooga, is the only area science museum putting on a special event for the celestial spectacle that's taken place a mere six times since the telescope's invention.
Several activities are planned.
The museum will aim its 20-inch-diameter telescope at the sun and show the image live on screens in its observatory, which seats several hundred, while Dundee and other museum staff give commentary. Venus starts passing in front of the sun at 6:09 p.m. and viewing will last until the sun sets around 8:40 p.m.
Smaller telescopes will be set up outside the science center to allow visitors to watch Venus' transit.
Tellus' planetarium also will show a program on its digital projector about the celestial event.
The program includes the story of Capt. James Cook, the British explorer, who sailed to Tahiti in 1768 to construct an observatory to see the transit the following year. By combining those observations with data collected from around the world, astronomers were able to accurately calculate the distance between the Earth and the sun for the first time.
The technique of watching stars to find celestial objects is still in use today, he said. NASA's Kepler space telescope searches for far-off Earth-like planets by looking for tiny dips in the brightness of a star when a planet crosses in front of it.
The transit of Venus will be viewable in all U.S. states, but Dundee recommends against trying to look at the sun directly through a filter because it can be hazardous to vision unless you know what you're doing. Besides, Venus will be a tiny speck on the surface of the sun, he said.
A better idea is to use a pinhole project, in which a piece of paper or cardboard with a pinhole in it is held above a white piece of paper on which the image of the sun is viewed.
Easiest and perhaps best of all, Dundee said, is to search on the Internet for "transit of Venus."
"There are lots of opportunities for armchair astronomers" to view the event online, Dundee said.
The Smith Planetarium of Walker County Schools outside Chickamauga, Ga., is still undergoing renovations, so it won't be open for the transit of Venus. Its new digital projector should be installed in mid-June, said Shirley Smith, whose husband, Jim Smith, is the observatory's namesake.
The Smiths, who are longtime skywatchers, will likely use a simple pinhole projector to look for the transit, she said.
"Very simple. Two pieces of paper. One with a pinhole in it," said Shirley Smith, who's used pinhole projectors in the past. "I can't say I've seen transit of Venus. But I've seen sunspots, things like that."
The Associated Press contributed to this report.