I am looking to make a hemicyclium-type sundial (half-hemisphere) in a metal working class. What little I can find on them says they are inaccurate, without being very clear on the problem. It appears to me the only issue is it needs to be tilted so that the gnomon aligns with the Earth's rotation axis; thus the half-bowl faces south and the gnomon points south, but the end of the gnomon that attaches to the bowl points north. Am I missing anything? I am also looking to use an analemma-shaped gnomon to cast the shadow on the bowl, and at least month lines for the solar elevation. The bowl will also have a rod and bracket on the bottom to allow it to be rotated for daylight-savings time and for local longitude corrections.
Thanks in advance -- Brad
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