Search This Blog

Wednesday, June 6, 2012

Shooting Venus

Contrary to all weather predictions from both NOAA and Environment Canada, the skies in the Strait of Juan de Fuca and on Vancouver Island were crystal clear this afternoon for the Venus transit. I brought my sextant with me on the boat just in case, it proved to be an excellent solar telescope.

After we passed the Romeo buoy I got the idea to try to shoot Venus during the transit as a celestial Line of Position. The boat was bouncing in the seas pretty well and I had to shoot through one of the wheelhouse windows, and I only had time for one very sloppy sight. My intercept turned out to be 0.8 nautical miles from my GPS position, meaning I was very lucky. Here's the raw data:

Watch Time: 16:58:04 pdt (+7), 5 June 2012 Height of Eye: 20 ft Instrument Correction: 0.0'

GPS Position: 48° 18.4'N 123° 04.6'W Course Over Ground: 303°T Speed Over Ground: 27.4 knots

Wind: 25 knots westerly Seas: 4 ft

Sextant Height (Hs): 38° 51.2'

Intercept: 0.8 nm Away Zn: 261.2° T

The red dot in the illustration is the actual GPS position of the boat, and the green line is the Line of Position for Venus.

All in all, a very good day.


  1. Nice! I had about ten minutes of sunshine here in Ballard and was going to watch with a pinhole camera, but the clouds closed in again. Rats.

    One question: since Venus was crossing the face of the sun during this would you have expected substantially the same result if you'd just taken a sun sight? In other words, anything special you can glean from shooting Venus in transit?

    1. Not a bit, the lower limb of the sun would have been a much better choice from a navigation standpoint. This was purely "art for art's sake". But it may be that nobody else has ever done it, and sextants will probably be museum pieces by the time it happens again. So there it is, my ridiculous claim to fame. ;)