Easter Island: Transit of Venus (2/3)

This is the second of a three part post series on our recent trip to Easter Island. Previously I wrote about the outreach activities we did on the days leading up to the transit. In this post I describe the main event itself: the transit of Venus.

I've previously talked about the transit of Venus (here) and described the math involved in determining the distance (here). Hence, I'll skip the overview and jump right into the details.

We gathered at Ahu Tahai, a ceremonial site with several moai located near to the museum at the edge of Hanga Roa, the only town in Easter Island. We had been promoting the event for several days and the island is so small (4000-5000 inhabitants) that pretty much everyone knew what was going on.

We had set up several telescopes, sun-spotters, and had many eclipse viewing glasses. Several people brought their own telescopes, though, so we had even more equipment with which to view the transit. That turned out very useful given that over 1,000 people showed up to watch the transit. That's an impressive number, but sounds even cooler if you say that "20% of all people within a 4,000 km radius showed up." We were very excited to see such a huge turnout.

The crowd gathers to watch the last transit of Venus of the 21st century at Ahu Tahai.

The weather also cooperated: we had mostly clear skies and saw the transit uninterrupted for over an hour. Afterwards the Sun got low on the horizon and there were some clouds there, but we still managed to spot it from time to time in breaks amidst the clouds. Although the whole transit lasts for about 6 hours, here at Easter Island we would only able to observe for about 2 hours. The fact that we got at least half that time was excellent.

The transit of Venus captured by Jackie Faherty (U. Chile). Sunspots can be seen near the center and some clouds are rolling in oposite to Venus (the large black dot). Additional photos can be found here.

In particular, the time we observed was near the beginning of the transit. In order to measure the distance one needs accurate times of the ingress interior or ingress interior (see my post on how to determine the distance for more information). We were able to time ingress interior thanks to the weather. The predicted time was 16:28:18 local time and, though we split on several teams, Francisco Förster, Helene Flohic, and Milena Bufano win the prize of getting closest to the predicted time: 16:28:10.

Our fearless leader, Jackie Faherty, had spread the news of our effort in order to collaborate with school groups from across the planet. You may have seen the article on Universe Today on this effort. We are pleased to report that we had about 20 school and outreach groups onboard for this measurement including the good folks of Astronomy Live at UCLA. Here's a map of our network:

The Hetu'u Global Network.

We had people in the US (New York, Florida, Texas, California, Hawaii), Australia, Japan, Hong Kong, Colombia, India, Iran, Holland, Denmark, and, of course, Team Hetu'u at Easter Island. Here's a flickr set of many of the photos from the individual teams.

We've heard back from most of the teams, but many suffered from clouds, rain, or otherwise missed the contact times. That's understandable given these sorts of efforts, but we at least have 7 teams reporting second contact times (and a handful reporting third contact times).

Here is our result:

The large black circles are the measurements while the smaller open ones are the predicted values.

Combining the measurements together we estimate a distance to the Sun of 151 +/- 20 million kilometers. The Astronomical Unit has a value of 150 million kilometers so this is not bad. At that time of year, the Earth is a bit more distant (1.015 AU) so the distance should have been more like 152 million kilometers. Still, this is far better than we expected! It's great that we got such spread out baselines too (Australia and Texas, notably). Our work is also mentioned on a few AMNH news posts here and here.

Overall I have to say that this was a huge success. We inspired many of the kids on the island about the wonders of astronomy, got the public interested in the transit viewing, were able to successfully see the transit, and got a good measurement of the distance between the Earth and the Sun. Many thanks to everyone on Team Hetu'u for all their hard work!

Additional photos of our event can be found on Jackie's flickr set here.