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For the last three night 2/17/21, 2/18/21 and 2/19/21, about 20 minutes after sunset, a light arch has appeared in the western sky. Sometimes there are multiple arches (as in this photo). Does anyone know what this phenomenon is? I’ve taken sunset photos here for years but I’ve never seen this till 3 days ago. I have searched online but have not found an explanation of this arch of light above where the sun had set twenty minutes ago.