As Tuesday afternoon unfolds, celestial observers in the South Sound will turn their attention to the sun, as Venus moves across its face. If the weather allows, this will be the last chance to see the transit for another 105½ years.
Astronomy professor Dana Rush will try to sneak a peek at the event between classes at Pacific Lutheran University and Green River Community College.
“It would be something else I can put on my astronomical bucket list,” Rush said.
The event will begin at 3:06 p.m. PDT. At 3:24 p.m. Venus will be completely within the disk of the sun. As it crosses the northern half of the sun, Venus will reach the center of the sun at 6:26 p.m. The entire event will last about six hours. Here in the Pacific Northwest that means the sun will set at 9:02 p.m., before Venus completes its transit.
If you want to see the whole celestial show, you’ll need to fly to Hawaii.
“The West Coast of the United States and the Pacific are two of the prime regions to view the transit,” Rush said.
Even though Venus is about 3 percent of the Sun’s diameter, the planet will appear as an obvious but small black spot to naked-eye observers, according to Astronomy magazine.
Rush said the cycle of Venus being in proper alignment for the transit to be seen makes it a rare event.
“It happens in pairs spaced eight years apart. They are on a cycle where each eight-year pair is separated by 105 1/2 years and then 121 1/2 years,” he said.
The last time the transit could be seen was 2004, seen mainly in Europe, Africa and Asia.
Beyond the rarity of it occurrence, the transit also has historical significance for astronomers.
English astronomer William Herschel suggested measurements could be taken of Venus touching and leaving the sun from different places on Earth. Using those measurements and trigonometry, Rush said, one could determine the distance from the Earth to Venus and the sun.
“Once we understood the distances in the solar system, we began to understand how big space is,” Rush said.
“It’s this historical tradition that makes it exciting, a connection with the past,” Rush said of the transit.
The biggest issue for observing the transit is the weather. Forecasts late last week called for partly to mostly cloudy skies on Tuesday.
“June is a crap shoot. I tell my astronomy students this is not Arizona. We take what we get here,” Rush said. “I’ve been teaching for 21 years, but I haven’t learned how to part the clouds on demand.”
If you miss this week’s transit, you might be out of astronomical luck. The next transits will take place Dec. 11, 2117 and Dec. 8, 2125.
VIEWING THE TRANSIT
Tacoma Astronomical Society: Members will have solar scopes and other equipment available for the public to view the transit of Venus starting at 3 p.m. and ending at sunset, weather permitting. They will be located at the Central Meadow of the Chambers Bay Properties in University Place.
Pierce College-Fort Steilacoom Campus: Astronomy students will be outside the Rainier Building with telescopes and projection equipment from 3-9 p.m. If it is cloudy, visitors can see the transit via live video stream inside. There also will be public lectures on the historical and astronomical significance at 4, 6 and 8 p.m. in Rainier Room 361.
Goldendale Observatory State Park: The park in Klickitat County will have a viewing 3 p.m. to sunset. Visitors have the chance to watch this transit live from the observatory’s solar telescope. Video from the telescope will be displayed on the large monitor in the interpretive center indoor theater.
• Do not look directly at the sun with a telescope, binoculars or naked eyes.
• Find an observing spot with a clear view to the west and a flat, unobstructed horizon toward the west-northwest where the sun will set.
• Buy a sun filter to use on a telescope.
• Purchase a pair of eclipse glasses. You can find them online.
• Look at the sun through welder’s glass. Be sure it is No. 12 or 14 glass.
• Point a telescope or binoculars at the sun and project the image on a piece of paper on a wall.
• Use a mirror to project the image onto a wall, paper, or screen.
• Build a pinhole camera. Punch a hole the size of a pencil in a piece of cardboard or thick construction paper. The image of the sun will show up on a screen or paper behind the hole. The greater the distance between the two, the bigger the image but also the less defined.
Source: Dana Rush, astronomy.com