I recently came across this posting on measuring Naked Eye Limiting Magnitude and decided to give it a try for my home. We live very close to Exmoor National Park which is now designated a Dark Sky site, so I was hopeful of a good result.
Last night the seeing was better than average. Not stunning — the Milky Way wasn’t visible, for example, which it is when the seeing is excellent. Once Kochab was higher than 60° above the horizon I gave my eyes a chance to fully dark-adapt and then had a good look at Ursa Minor. The main asterism stars were clear as were 4 UMi and 5 UMi. Towards Polaris star 10 was definitely visible, and I thought I could see star 12 with averted vision, but I couldn’t see star 11. It’s possible that the collection of stars around 12 were visible as a whole, but 11 on its own between ζ UMi and η Umi wasn’t. So, I’ll settle for star 10 being the limit of magnitude for yesterday evening, giving a NELM figure of 5.55.
I’ve always estimated the NELM for this location to be between 5.5 and 6.0, so I’m happy with that result. It will be interesting to repeat the experiment when the seeing is particularly good.