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Message: <blockquote data-quote="Binastro" data-source="post: 3169524" data-attributes="member: 111403">. Projecting the Sun is quite easy using a small hand mirror with a mask giving a clear mirror of, say, 3 to 5 mm. So don't be put off by the comments of using an astronomical star diagonal.The refinement using an astronomical star diagonal is complicated by the fact that the mirror is recessed in its housing.Sometimes the back plate of the star diagonal has 3 or 4 screws. you can take the back plate off and then usually you can just use the mirror which is stuck to the back plate. The problem here is that inevitably you will get fingerprints on the front surface mirror. These fingerprints may be difficult to remove and may etch into the surface of the mirror.but an astronomer can probably position a star diagonal with the barrel removed so that good projection is achieved.On March 20 the Sun is 1922 arc seconds across. This is a little over 32 arc minutes and a little over 0.5°.The diameter of the image of the sun on a screen or a white wall is 1/107th the projection distance. This is for a theoretical infinitesimally small mirror.At a 5 m projection distance such an image would be 46.6 mm across. Using a real 3 mm mirror this, I think, gives an image 49.6 mm across. So the sun's image is 5 cm across as mentioned previously.British summertime comes in on March 29, so I presume that Europe also has wintertime on March 20. So daylight saving time does not complicate matters regarding time.</blockquote>

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