Sunday, June 10, 2012

Transit of Venus

Transit of Venus - June 5, 2012
It was a very cloudy afternoon.  I went outside at work just as the transit of Venus started but there was almost total cloud cover.  A few minutes into it the clouds cleared and I got to see Venus against the Sun for about 5 seconds.  I thought that might be all I would see because heavy dark clouds were rolling in.  On the way home the clouds broke up for a little but traffic was terrible.  I had my camera and binoculars in the car.  As soon as I got home I set up my camera and got this photo as more clouds were rolling in.  Five minutes after I got home there was total cloud cover. Later I noticed clear skies to the southwest so I drove that direction until it was clear enough to see the Sun.  I watched the sunset through binoculars and took more pictures.  It seemed to give a little depth of field to the solar system.  In fact the transit of Venus was used to calculate the distance from Earth to the Sun and from there calculate the distances of the other planets.  Observing the transit of Venus in 1769 was one of the main goals of Captain James Cook's first expedition.  Although moving clouds and Venus against the Sun seemed to create a depth of field it is still difficult to imagine the distances and sizes of the Sun and the solar system.  Venus is just a bit smaller than Earth but it is much closer to Earth than the Sun (Venus is about 30% of the distance to the Sun).  I understand how the distance to the Sun can be calculated from observations of the transit of Venus from different locations on the Earth but I am amazed by the instruments they had 250 years ago to take the measurements.  The world today is so automated it's difficult to imagine and appreciate how clocks, telescopes, sextants were designed and made.  Not to mention all the precise measurements of the orbits of the planets and the calculations (without calculators or computers) that led to the predictions of when the transits would occur.