Moon-Venus Conjunction 7/18/15

  Last evening the Moon 2 days past New skirted a couple of degrees south of Venus.  I left for work a little early and stopped by Ludington Harbor to photograph the pairing. 

   In the photo above you may have noticed that the lighthouse in the foreground appears to be illuminated by a camera flash.  The screengrab below shows the Google Distance Calculator's measurement of the lighthouse-camera distance at 1790 feet.  To achieve that level of lighting with a standard camera flash you would need one with a guide number of 2500.  Here is the calculation.

 Guide Number = (distance/f-stop) X (ISO/100) = 1790/5.6 X 400/100 = 2506.  A quick check of consumer aftermarket flashes finds that for $1000 you can get a device with a guide number of 262.  Luckily I didn't need an array of expensive flashes to provide fill-flash, because  The Manitowoc lake freighter was pulling out of the harbor at the time and was shining its spotlight on the channel marker for navigation purposes. 

   

1790 feet

  Here is a close-up view of the pairing taken with my 500 mm lens.

   With the similar geometry of both the Moon and Venus being between the Earth and Sun they share a similar backlit crescent shape.  The Moon was 9% lit while Venus displayed a 19% lit crescent. The Venus inset in the photo below appears fatter than 19%  because it is overexposed due to its greater reflectivity.