June 5, Transit of Venus

June 5, 2012 Today, we are watching the "Transit of Venus".  This occurs in pairs about every 130 years.  The pairs occur about 8 years apart.  Today is the second of this century's pair, the first occurring in June 2004.  Basically, it is the same as an eclipse.  We are looking at the sun's disc, with a small black spot on it which represents the dark  side of Venus.  We are watching with binoculars which have a "solar filter" taped over the front.  This filter is very, very  dark.  We cannot see anything except  the sun's orange disc through the binoculars.  There are also six small black sun spots visible besides Venus.  Since we are on a rocking boat, it is hard to acquire the sun in the field-of-view of the binoculars and keep it there.  In addition, the boat is constantly yawing in the wind.  Sitting in the cockpit, the sun frequently disappears behind the boom or solar panels over our head.  Watching would be easier on the beach of the bay we are anchored in, except for the fact that there is a little surf hitting the beach today.  The likelihood that we could make both a successful landing and subsequent departure from the beach in our dinghy while keeping the binoculars dry is not convincingly high.  Instead, it is a, "I don't think so".

Why are we interested in this?  Well, history for one, and also our joint interest in astronomy.  One of the prime scientific assignments on one of Captain Cook's four incredible voyages was to view a transit of Venus in Tahiti.  For that transit, astronomical teams were sent to a number of locations around the world.  The plan was to take precisely timed measurements of when Venus just started to obscure the edge of the sun and was first entirely within the sun's disc, and similarly when exiting the sun's disc.  Analysis of the data would provide astronomers with a measurement of the distance of the sun from Earth.  Realize that at a number of locations, it was cloudy at least part of the time and also that clocks were not very good during that era.  This was before Harrison built the first successful chronometer.  The transit data would be used in conjunction with other astronomical observations to calculate books of tables that mariners could use to calculate their longitude in the world.  

Point Venus, Tahiti....
I think they chose wisely to skip it.

When we sailed across the South Pacific in 2000, we anchored next to Point Venus when we were at Tahiti.  Point Venus is where Cook's team made their measurements.  There is a large monument commemorating the event.  We considered being there today in our planning earlier this year, but decided to spend the bulk of our allowed 90 days in French Polynesia  in the Tuamotu atolls and not go to Tahiti at all if we could avoid it.  Why only 90 days?  Because after 9/11, the USA limited tourist visas to only 90 days.  The rest of the world responded tit-for-tat.  Same reason US citizens now pay for expensive  foreign visas that used to be free.  So, if we have whetted your appetite to personally view the next two transits of Venus,  they will occur on 11 December 2117 and 8 December 2125.  Mark your calendars!  We plan to be there.  Hope to see you there, too.