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Here are two images of the face-on spiral galaxy NGC 3184 that I took about 6 weeks apart, the left image on 27 Feb 2016 and the right image on 8 April 2016. In between those dates (namely, on 21 Mar 2016), a "new" star pointed to by the arrow in the right image appeared. This was supernova 2016bkv, the explosion of a star inside NGC 3184 that was previously too dim to be seen from Earth (but after 21 Mar 2016, was very easy to see, at least photographically).