ANCHORAGE, Alaska (AP) -- A University of North Texas team plans to chase Venus from Alaska and Hawaii on Tuesday during the planet's rare transit across the sun.
It's a modern-day twist on a 1769 expedition to Tahiti by British Capt. James Cook and others in two other locations who set out to document the transit and try to calculate the earth's distance from the sun, based on a formula devised decades earlier by astronomer Edmond Halley. In 1716, Halley issued a call for scientists to fan out across the globe to witness the unusual alignment that would not recur until some 20 years after his death.
Venus transits come in twos that are eight years apart and separated by more than 100 years. The last transit occurred in 2004 and the next pair won't happen until 2117.
Tuesday likely brings the last chance for most to see it in their lifetimes, so scores of Venus events are planned around the world and people are hoping for clear weather to reveal a barely visible black dot crawl across the sun.
In Alaska, the UNT team of "citizen scientists" led by astronomy program director Ron DiIulio plans to track the action from Homer south of Anchorage because of favorable weather expected. They will not be using the grandfather clocks of Cook's day, but high-tech telescopes, atomic clocks and cameras including one equipped with a global positioning unit.
The transit takes place between 2:06 p.m. ADT and 8:47 p.m. ADT.
In Hawaii, another UNT team is setting up at Big Island's South Point.
DiIulio said the goal is to achieve a more perfect, accurate replication than the 1769 expedition, which raised doubts because of questions over times noted and the presence of an apparent haze -- called the black drop effect -- around Venus that made it difficult to determine exactly when the planet crossed over the sun's rim and when it exited.
Dilulio is excited to take measurements with a camera filter that will optimize the rendition of the sun for a far more accurate documentation.
"We're shooting some of our shots with that and we're going to measure it with that," he said. "We're thinking that cutting down on the amount of sunlight getting in just to that one area that we can reduce that black drop and get a better circle without that little floppiness underneath."