On the night of Apr 17/18, 2026, under fair conditions, Nicole Melso, three PHYS 373 students -- Donovan Barros, Hayden Quinn, and Cooper Ebbensen -- and I attempted to collect images of M51 for a project for one the groups in the observational astronomy course.
The weather was decent at sunset, with thin cirrus which gradually seemed to dissipate as the temperature dropped. We acquired images of the galaxy in B, V, R. If the center of M51 is placed at (851, 713) on the sensor, then a faint star appears in the guide camera. We were able to guide on that star with 10-second guide exposures.
One small mis-step we made was to acquire dome flats in a non-standard manner. Usually, I wait for complete darkness to take flats, so that the only source of light illuminating the white card comes from the lamp inside the dome. This evening, because I feared clouds would arrive soon after sunset, I wanted to start observing M51 as soon as it was dark; so, we started taking dome flats when the Sun was only 1 to 5 degrees below the horizon. Moreover, with the dome door open, quite a bit of light from outside filtered into the dome and fell onto the white card. It wasn't obvious at the time, but when one applies the flats to the target images, there are significant residuals at the positions of specks of dust on the filters. Normally, those dust donuts are removed cleanly via dome flats ... but not so much tonight. Rats.