Transit of Venus June 5, 2012

by Ira Polans

From the base of Kitt Peak, you can see the domes of the various telescopes along the ridgeline.

From the base of Kitt Peak, you can see the domes of the various telescopes along the ridgeline. Photo: Ira Polans

In 2004 when Venus last transited the sun, I was not yet a member of the AAAP. While I had made plans to observe the event, the plans did not work out. Realizing that the 2012 transit would be my last chance to see one, I decided to maximize my chances. After researching the options, my wife and I took a trip to Tucson, AZ to view the event.

Tucson was chosen because it has several advantages over the Northeast. The main one being that there would be a small chance of a cloudy sky on the day of the transit.

The famed McMath-Pierce Solar Telescope

The famed McMath-Pierce Solar Telescope. Photo: Ira Polans

Another attraction was that Kitt Peak National Observatory planned a special program for the transit. Also, my wife’s parents had retired to the Southwest. This trip would give us a chance to spend some time with them.

The trip from Tucson to Kitt Peak is about 60 miles. However since part of the trip is up the mountain, it takes about 90 minutes to get there. Most of the drive is through the Sonoran desert, which is famous for the Saguaro cactus. To me, any part of the Southwestern landscape is beautiful, and this part of the desert I hadn’t seen before. The last part of the trip is the ascent of the mountain on a winding road. The ascent is about 4000 feet. When you arrive at the summit, you drive past a few domes to the Visitor Center which is at 6875 feet.

Ira During the Transit

Ira in front of the heliostat mid-transit. The Sun’s image at the bottom is computer plotted. The Sun’s image at the top is the projection from the heliostat.

The Visitor’s Center contains a small museum, a 20” telescope, and a heliostat. For the transit, they also had several amateur telescopes in the courtyard, binoculars, and a sunspotter solar telescope. Of course all the optics had the proper filters. In addition all attendees of the transit program received eclipse shades for safely viewing the sun.

Check-in was at 2:00 pm and the transit began at 3:05 pm. The heliostat projected the image onto a screen about four feet tall. While I knew there would be scopes outside, I thought it would be best to watch second contact here. When the transit began I was surprised by two things. The first was how big Venus appeared against the Sun. The second was how long it took Venus to separate itself from the Sun’s limb. I was aware of the back teardrop affect, but to me and many others in the room, Venus just seemed to stick to the limb.


View from the bottom of the missile silo looking up showing the partially retracted silo door. It is locked in this position so the Russians know this is not an active missile base. This missile when operational could have delivered the largest warhead in the US arsenal.

Historically a transit of Venus was important because it allowed astronomers to figure out how big the solar system really is. Without an event likes this, the best astronomers could do was measure the relative distances between planets. By using trigonometry, parallax, and accurate timings of second and third contact, along with Kepler’s third law they could finally figure out the actual distance from the Earth to the Sun. And once they knew that they could figure out the distances to the planets.
To give the attendees a better idea of the effort involved in applying this technique, Andrea Wulf lectured us about her book “Chasing Venus: The Race to Measure the Heavens”. In her lecture, Andrea told us about how 18th century astronomers worldwide worked together to capture the information need to make the calculation during the transits of 1761 and 1769.

As previously mentioned the Visitor’s Center has a 20” telescope. As the Sun began to set, the telescope was put into use. Rather than look at the Sun and the transit, we had a chance to see Betelgeuse and Sirius. This was possible because the telescope is computerized.

During the trip I had the opportunity to tour one of the remaining Titan II missile silos and visit the Pima Air and Space Museum. Both of these are in the Tucson area.

This entry was posted in October 2012, Sidereal Times and tagged , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s