June 2012

A transit of Venus, when the planet moves directly between the Earth and the Sun, is a relatively rare event. Since the orbit of Venus around the Sun is tilted at an angle compared to the Earth’s orbit, most of the time Venus appears to go above or below the Sun as it passes by. But every now and then it is lined up just right to pass directly in front. This last happened in 2004, and the time before that was in 1882. If you missed it this year, you can catch it next time in 2117 — yes, that’s more than a century away! If you didn’t see pictures of this event in any of the fairly extensive media reports, you now have your own record here in this email, direct from the staff of LO! Many people may think “What’s the big deal about seeing a little black dot move slowly across the Sun?” But there is a long history of astronomers being sent all over the world to observe these transits in the 18th and 19th centuries because carefully timing these transits can be used to calculate precise distances in our Solar System. As an adolescent I learned that no transit of Venus would occur during the 20th century, but I realized that when I was an old man, I’d have a chance to see one. So I’ve been waiting more than 50 years for this event!

The three pictures attached reflect various stages of the event. This first picture was taken at 3:11 PM Pacific Daylight Time (PDT), when the planet was just starting to move in front of the Sun. The “notch” in the Sun’s edge shows Venus is only about halfway in. The next picture, taken at 4:03 PM PDT, shows Venus well on it’s journey across the Sun. The last picture, taken at 5:49 PM PDT, shows the planet nearing the halfway point in it’s crossing. Shortly after that trees blocked our view, and the sun set in California before the transit ended. Contrary to the weather prediction, intermittent clouds interfered a bit with picture taking. Due to atmospheric turbulence the first picture is rather blurry, but the other two can be considerably enlarged to reveal some detail in the many sunspots (look like freckles) on the face of the Sun. These are cooler areas of the Sun’s surface (“only” about 7000ºF) compared to the rest of the surface (about 10,000°F). They form and disappear in a matter or days or weeks, so the view is constantly changing.

Technical stuff: The photographs were taken with a Canon EOS 1000D camera (a digital single lens reflex) pointing through a 6-inch diameter Newtonian-Maksutov telescope equipped with a solar filter and a 2X Barlow lens for an effective focal length of 1460mm. The exposures were 1/800 of a second at F/9.6 at ISO 200. Minimal processing was done other than what the camera does automatically to produce JPEG files.

I hope you enjoy these photos.

Carter Mehl,

(Sometime) Resident Astronomer,

Lookout Observatory Southern Outpost

Albany, CA