The transit method to determine Earth-Sun distance (and therefore the value of the Astronomical Unit) is based on the effect of perspective. According to this effect the position of Venus on the solar disk seen simultaneously from two points of the Earth changes.
This activity consists in the use of the simulation program SimTV. This program simulates the observations of a transit of Venus from anywhere on Earth. In this activity the students will take two or more photographs from different locations to be able to determine the Astronomical Unit. We propose two different methods of realization. The first method is to observe the transit from different places. The second method is to measure the contact times from different places.
This measurement method based on the observation of the transits of Venus was proposed by Edmond Halley in the late seventeenth century. Since the late nineteenth century other methods with more accuracy have replaced Halley's.
Astronomical Distances: Activity 3
The Sun-Earth distance
In the attachments you can find an activity guide for students: Activity 1,(1st method), Activity 1(2nd method) and a teacher's guide (1st method).