The same plate from the previous post.

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1. Robert McNees (mcnees@mastodon.social)'s status on Friday, 06-Oct-2023 15:41:04 UTC Robert McNees

   in reply to

   You can see three marks "N" on the plate where Hubble identified novae.

   Comparing with a plate taken the night before, he realized that the brightness of one was changing. Recognizing a Cepheid variable star, he crossed out the "N" and wrote ‘VAR!’

   Here are the plates side-by-side. H331H was taken the previous night, a 40-minute exposure with poor seeing conditions. Plate H335H, which revealed the Cepheid, was a slightly longer exposure under better conditions.

   Image: Carnegie Observatories