Exercises in Photographing Mercury in front of the sun
and in Measuring its Position

First off all and most important:
NEVER try to photograph the sun without using a solar filter (made from glass or film) in front of the telescope/camara lens!

Detailed annotations about building solar filters, mounting the camera, ... can be found on Tim Cole's noteworthy page Solar imaging with a digital camera, in an article of "Sky and Telescope" and in Fred Espanak's Transit of Mercury 2019 page.
On this page we only give short tips in order to motivate the participants doing exercises early before November 11th.

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1. Digitally photographing of the Sun
2. Multiple exposuring
3. Measuring Mercury's position on the solar disc

1. Digitally photographing of the Sun

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2. Multiple exposuring

As described in the basic ideas of this project we propose to photograph the sun twice with fixed camera in order to be able to determine the position angle of Mercury with respect to the direction to west. Afterwards, these pictures can (but must not!) be superimposed using a software like ImageJ. The difference in the pixel positions of the sun (in the two single pictures or in the combined picture will show the westward motion of the sun due to the earth's daily rotation.
Preconditions of this procedure are, of course, that

The following hints may be useful:

For the processing of digital images we recommend the public domain program ImageJ. But there are many other programs offering appropriate manipulating possibilities. The following advices refer to "ImageJ".

The combination of successive photos can be done by the following steps (sequence of menu items to be followed in red):

  1. Open the images simultaneously with the program: File → Open

  2. Stack the pictures: Image → Stacks → Images to Stack
  3. Combine the pictures laying one "upon" the other (in the z-direction): Image → Stacks → Z Project.
    Following kinds of ZProjection should be tested:
    • Average Intensity
    • Max Intensity
    • Sum Images

    In most cases the max-option seems to yield the best results. (The pictures have been taken with little experience with a new camera and at difficult weather conditions.)

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3. Measuring Mercury's position on the solar disc

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Editor: Udo Backhaus
 last update: 2020-02-11