Simultaneously photographing Venus in front of the Sun

The transit will look slightly different when being observed from different sites on Earth. As an example the following pictures, made by the observatories of the Global Oscillation Network Group (GONG) of the National Solar Observatory (NSO) show this parallax effect between Udaipur and El Teide:

Simultaneous 2004 transit photos
transit1 transit2
Udaipur, India, 7.30 UT     El Teide, Canares, 7.30 UT

But the angular differences will be smaller than the apparent radius of Venus. They will be remarkable only by combining simultaneously taken pictures or by exact measurements. The picture below is the exact superposition of the above Udaipur and El Teide pictures.

The combination makes the parallax of Venus visible.

This project's aim is to determine the distance to the Sun by comparing the positions of Venus on pictures which have been simultaneously taken from distant sites on Earth. For this reason, it will be necessary to take photos with precisely known orientation at exactly concerted moments at as many sites as possible.

In additional pages we

In principle, two simultaneously taken photos are sufficient for determining the distance to the Sun. However, our experiences made during the 2004 transit of Venus have shown us that the errors which are due to bad focussing, the process of digitizing, the measuring of positions etc. make it unlikely to get a satisfying result on the basis of two photos only (but look at the evaluation of two 2004 transit photos in the example!). Therefore, as many pictures as possible should be combined in order to minimize random errors by statistical methods.

Editors: Udo Backhaus
  last update: 30.04.2012
Stephan Breil