Figure 1 – Dinah looking for clear skies (c) DEWolf 2025

I keep notes on what I do with my telescopes! For the last two months I have been trying to collimate my Nexstar 8 SE. Collimating a Schmidt Cassegrain telescope is not easy, but also not overwhelmingly difficult. On May 7th I did a proper laser alignment and have been waiting for clear skies to finalize it with a star collimation, and waiting, and waiting … I’ve had rain and more rain and when it wasn’t raining dense clouds. Dinah is forlorn.

My prophet-apps finally predicted four clear sky nights in a row this week. The first was last night and what did I get – Canadian wild fire smoke!!! Can’t we get rid of it with a tariff or something?

I’ve had nothing to do but think about this. The big issue is what your minimum or limiting magnitude is, the dimmest star you can see. The first point is the aforementioned Bortle number. Bortle, as we discussed, is a measure of light pollution. I am working under Bortle 5.7 skies and I asked Chat GPT to give me a plot (Figure 2) of limiting magnitude vs Bortle number.

Figure 2 – Limiting Magnitude vs. Bortle Number

So on a perfectly transparent night, my limiting magnitude should be about 5.2.

Now the other factor to consider is the transparency. This is usually about 0.3 to 0.5 for my skies meaning there is a reduction of limiting magnitude by about 0.3 to 0.5. So last night it should have been and was predicted to be about 4.8, which seems about right to me. However, the faintest star I could see was Spica or Alpha Virginis at magnitude 1.0. Yikes!

Dinah, who comes from literature herself, paraphrases Alexander Pope from his Essay on Cats, “Hope springs eternal in the feline breast, cat never is but always to be blessed.”