Essen, horizontal view
Observing, Photographing and Evaluating the
Transit of Venus, June 8th, 2004
Essen, equatorial view
Tips and Instructions for the Transit Day
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 different 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.
The basic ideas and an evaluation example are again described in
In principle, two simultaneously taken photos are enough to determine the
distance to the Sun. However, our experiences made during the transit of
Mercury last year have shown us that the errors which are due to bad
focussing, the process of digitizing, the measured positions etc. make it
impossible to get a satisfying result on the basis of two only photos.
Therefore, as many pictures as possible should be combined in order to
minimize random errors by statistical methods.
The participants are asked,
- to photograph Sun and Venus during the transit all quarters of an hour, i.e.
exactly at 5.30, 5.45, 6.00, ..., 11.00, 11.15 UT.
- In the case that clouds make photographing impossible at the fixed moments, as
many pictures as possible should be made with similar time difference. By line
fit it then will be possible to interpolate the positions being desired later.
Tips for Photographing
- Little sensitive films (e.g. 50 ASA or 64 ASA) seem to be most suitably.
- If you let develop the films in a foto shop don't let them cut into parts
or frame the slides! The borders of the pictures will be hardly to detect.
- The correct time of exposure must be found by series of test pictures, in
advance. (By using a sun filter and an optic with f/10, we found 1/1000 s to
be the best.)
- The focal length should be chosen so that the pictures show an as large part
of the Sun as possible. Even better, the pictures should be large enough to
show two pictures of the whole Sun. (With a picture size of 24mm*36mm focal
lengths of up to ca. 1000 mm are suitably.)
- For precise determination of the picture's orientation, we strongly propose to
make twice exposed pictures with a camera which is fixed on a tripod. We,
additionally, propose a time difference of exact 120 s. In that case,
both pictures of the Sun will hardly intersect.
- For each picture, the moment of exposure and the corresponding time difference
must be exactly recorded.
- Digitizing of analog pictures should be done by using a scanner for color
slides or by a professional photo shop.
- The best photos should be uploaded into our forum. Thereby, the file name must
give the most important information:
- Additional tips are given in the page Twice Exposed Pictures.
There exist several tools for measuring the positions of Venus with respect to
the Sun's face. In this project, we offer the program Bildauswertung.exe.
It is contained in the zipped archive. With
that program, the sizes and positions of Sun and Venus on digitized pictures
(BMP or JPG format) can be measured by fitting to them circles of variable
size and position.
Additional measurements during the transit
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last modification: March 28th, 2008