The last time Venus was seen with the naked eye was the year the United States banned polygamy – 1882. The next time will be Tuesday.
As the sun rises, a black circle will be seen moving across its diameter from 6:20 a.m. to 7:06 a.m. That circle will be Earth’s second-closest planetary neighbor, Venus.
“The last Venus transits were pivotal for finding the distance from the sun to the Earth, which is essentially the meter stick of the universe,” said Richard Pogge, professor of astronomy at Ohio State. “Measuring cosmic distances is one of the most important astronomical questions.”
The distance from the Earth to the sun had been sought for hundreds of years, with the earliest attempt being made by Aristarchus of Samos circa 300 B.C. The distance between the two is known as one astronomical unit – the equivalent of 93 million miles – and is often used with measuring space distances through parallax, said Bill Kramer, president of the Columbus Astronomical Society.
Scientists today are able to learn a lot less from a transit than their predecessors, who first studied it in 1639, did. Today, cosmic scaling is done mostly by bouncing radar off cosmic bodies and receiving precise measurements. When radar was introduced in the 1950s, it was the best scientists had, said Gerald Newsom, vice chair of the atronomy department at OSU.
“Astronomy is like a Playboy magazine – you can look all you want, but you can’t touch. With the advent of space probes, including those that visited Venus, there is little that Earth-based telescopes will learn unless there are surprising results with modern instruments,” Kramer said. “The Venus transit does not really provide us with an opportunity to do any hard science, except further verify the accuracy of the prior measurements.”
The transits have an irregular period, occurring in eight-year pairs every 121 or 105.5 years. Venus’ orbit is tilted with respect to the sun; if the orbits were aligned perfectly, the transits would occur in perfect intervals, Pogge said. The Earth, Venus and the sun then are aligned only in the line of nodes, which occur near December 10 or June 10, he said.
“(The transits are) pretty rare. It’s like, ‘When do all the hands of the clock line up?’ Noon – that’s the easy one; then another around 1:05 and a few other times,” Pogge said. “Now, if the hands are tilted, like the planetary orbits, it is even less common for them to line up. What you have (with a transit) is a fairly difficult cosmic clock.”
Different parts of the world will have different views of the transit, if any at all. The western United States will not be able to see it at all because it will be dark when the transit occurs. Areas of the Middle East, especially Iraq, will be in the prime location, with over six hours of viewing time, Pogge said.
No matter where one’s location is or how long the viewing time lasts, transits can be very damaging to the naked eye, he said. To view it best, search for a place with minimal obstructions that may ruin an eastern to north-northeastern view. Also, when viewing, it is important not to look directly at the sun. If looking at the sun is necessary, do so through eclipse or transit glasses, which are about $1 to $3 and are sold at Perkins Observatory in Delaware, Ohio, Pogge said.
For those who will not be awake at 6:20 a.m. Tuesday, they are not out of luck – a second transit of the pair will be on June 6, 2012. After that, Venus will not be seen from Earth again until 2117 and 2125.
