Position measurements

There are several tools for measuring the positions of Venus with respect to the Sun's face. In this project, we offer the program evaltransitpicts. With that program, the sizes and positions of Sun and Venus on digitized pictures (BMP or JPG format) can be measured:

Pixel radius and centre of the Sun are determined by fitting a circle to it.
By fitting a further circle to the second image of the Sun the amount and the direction of the Sun's displacement (and, thereby, the direction from East to West!) are determined. If the corresponding time difference and the celestial position of the Sun are known the scale of the picture and the angular radius ρ_S of the Sun can be derived from these values (see our example)
By fitting of two additional circles to both discs of Venus the rectangular positions x'=x/ρ_S and y'=y/ρ_S of them are measured with respect to the Sun's centre. The x-axis points to West, the y-axis to North.
The results are to put in an Excel sheet. which additionally calculates the line fits. An example sheet may serve as explication.
The completely filled (with the name of the observer, the city and the geographical coordinates) sheets may be uploaded via our data exchange page.

		Editors:	Udo Backhaus	last update: 21.04.2012
			Stephan Breil

Internet Project

Observing, Photographing and Evaluating the

Transit of Venus, June 5/6th, 2012

Position measurements