The Venus Transit: A Q&A with Dan Koehler, Associate with Yerkes Observatory at the University of Chicago (Part 1)


Patte:             Dan, thank you so much for inviting me to spend the day with you at this magnificent, once-in-a-lifetime event. Can you explain what we are about to see?

Dan:                Patte, it is a pleasure to have you here and I am very excited to share this wonderful event with you and your readers.

A “transit” of Venus … a passage of the planet in its orbit across the face of the Sun … is among the rarest of astronomical events. Due in part to the complicated relationship and geometry that exists between the two orbits of the planets, Venus transits, as viewed by observers on Earth, take place in pairs, and are always separated by exactly eight years. What makes Venus transits truly unusual are that the pairs alternate occurrences once every 105.5 and 121.5 years (during either the months of June or December), so relatively few people throughout history have seen one. In fact, only eight Venus transits have occurred since the invention of the telescope in the early 17th century. To complicate matters a bit more, the Sun must be above our horizon in order for us to see it. Both Venus and Mercury appear to pass directly in front of the Sun because both planets’ orbits lie inside Earth’s. Transits of Mercury, while still uncommon, happen thirteen times per century, on average, with the next opportunity to see our solar system’s smallest planet travel across the Sun’s face on May 9, 2016.

Q:     I can’t help but notice what looks to be scores of telescopes all over the mountain top with people galore. This is an amazing sight to behold.

A:      Well, today (June 5, 2012) is the big day! We have a sizable group of professional and   amateur astronomers, along with some lucky members of the general public, to witness         the second and last event of the 21st century’s Venus transit pairing onMt.Wilson, directly on the grounds of the Observatory some 5,000 feet abovePasadena. The previous transit in this current pairing occurred on June 8, 2004, and was not visible fromSouthern California. Prior to that event, Venus had not transited the Sun’s disk since December 6, 1882.

Q:     Can you give us a brief history of how the Mt. Wilson Observatory came to be?

A:      The Mt. Wilson Observatory was originally established in 1904 by George Ellery Hale as a solar observatory for the study and analysis of sunspots and numerous other detailed     structures and phenomena on the Sun’s surface.Mt.Wilson is the perfect location from       which to watch Venus’ silhouette move slowly across the solar disk … a process that takes nearly seven hours from start to finish and one that will not repeat itself until December 11, 2117. David Jurasevich, Superintendent of the Mt. Wilson Observatory and a co-host   of the three-day conference dedicated to an analysis of the Venus transits past and present, describes today’s event as “a most historic astronomical event observed from the world’s most historic astronomical observatory.”

Probably best known today for its 60-inch and 100-inch telescopes that contributed immeasurably to the study of stars and galaxies in the night-time sky,Mt.Wilson’s two century-old solar towers … one 60 feet high and currently operated by USC and the other 150 feet in height run by UCLA … continue Hale’s original solar studies on a daily basis. Operators in the two towers will be observing the Sun on today while a small army of astronomy enthusiasts employ a cadre of small to medium sized telescopes in various sizes and configurations … all equipped with special solar filters to safely view and photograph the Sun’s disk … in the observatory’s main parking lot to watch this rare spectacle that will start just after 3:06 p.m.

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