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Celestial News: Flashback — 2 transits of Venus

This week marks the 16th and 8th anniversaries of the 21st century’s only transits of Venus across the sun. The transits happened on June 8, 2004, and June 5, 2012. 

Transits of Venus are exceedingly rare. They occur in pairs, eight years apart, with over a century between pairs. There were no transits of Venus in the 20th century. One must go back to December 9, 1874, and December 6, 1882, for the previous pair of transits. The next pair won’t come along until December 11, 2117, and December 8, 2125, so if you missed the recent pair, well … enjoy the accompanying images.

Historically, transits of Venus across the face of the sun were used by astronomers to pin down the exact distance of the Earth from the sun and the exact size of Venus. Great expeditions were launched in 1761, 1769, 1874 and 1882 for the purpose of observing the rare events.

Nowadays, we have more precise methods of measuring sizes and distances in the solar system. Instead, observations of the recent transits of Venus were used to refine astronomer’s techniques in the search of transiting planets orbiting distant stars.

On June 8, 2004, I was set up with my 11-inch telescope and solar filter right beside the lighthouse on Tybee Island, Georgia, near Savannah, to greet the sun when it rose over the Atlantic Ocean. The transit of Venus was already in progress at sunrise. Once the sun cleared the horizon, I got my first view of Venus in front of the sun — one of those historic moments frozen in time.

I spent the next two hours photographing the event and attempting to capture the unusual black drop effect. This occurs when Venus just enters or exits the solar disk. The edge of the planet seems to stretch out like a rubber band. Of course, this is just an optical illusion, but the exact cause of the illusion remains a subject of debate. Not only did I see the black drop effect, but I managed to document it in photographs. I crossed it off of my bucket list.

Eight years later, on June 5, 2012, I was set up in Arches National Park near Moab, Utah, to watch the transit at sunset, this time armed with a special solar telescope (called an H-Alpha telescope) that allows you to see amazing details on the sun’s face.

With a little preplanning, I was able to set up my telescopes early in the day such that the sun would set right beside Balanced Rock, a 128-foot high miracle of erosion in the park. Nearby wildfires cast plumes of smoke across the western sky, making the sun and transit visible through a natural filter.

Venus is large enough that, with proper filtration, it can be seen with the unaided eye. The sight of that stark, black dot on the smoke-filtered sun suspended between the stone monoliths of Arches National Park was surreal, almost alien. I will never forget that once-in-a-lifetime view.

Venus repeats its position in the sky every 8 years, or nearly so. On Wednesday, eight years after the last transit, Venus once again passed between the Earth and the sun, but this time, it just missed crossing in front of the sun itself, passing off a little to the north. This event, called inferior conjunction, marks the transition of Venus from our evening sky into our morning sky. For the remainder of the year, Venus will adorn the predawn sky as our lovely Morning Star. 

Jimmy Westlake retired from full-time teaching at Colorado Mountain College Steamboat Springs in 2017, after 19 years as a professor of physical sciences. Celestial News appears monthly in Steamboat Pilot & Today. Check out Westlake’s astrophotography website at jwestlake.com.


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