Telescope Reviews: What is the DARKEST SKY you have observed?

Hmm.

Well, the faintest star seen with the naked eye is usually a function of the acuity of vision of the observer. Under the very same skies, I've participated in tests where the scatter in faintness seen was almost 2 magnitudes!.

It is the reason I bought a Unihedron Sky Quality Meter--to remove the subjective evaluation of NELM.

I think the best way to rate the night is to use star clusters with known magnitudes to seek the faintest star seeable in your scope. So far, I have just seen a star of magnitude 16.44 with my 12.5, but probably will be able to go deeper. This "back-translates" to well better than magnitude 7 visually, yet I cannot see, nor have even seen (to my knowledge) a star fainter than 6.8 with the naked eye.

I have observed in a sky DARKER than the recent magnitude 21.69 sky I measured at Mt. Pinos during exceptional conditions. And even in that darker sky, I could not see a star fainter than 6.8. I could see about 40% of all the Messier objects with the naked eye, yet I could not see a fainter star.

But in that darkest sky, the zodiacal light extended up from both horizons (appearing yellowish in color) to almost meet at the Gegenschein (which appeared like a thin cloud in the sky), and the rising Milky Way looked like storm clouds coming in. The bulge in the Milky Way extended PAST the two brightest stars in Libra, and the Milky Way in Cygnus was grainy and covered with literally hundreds of stars. It was so dark, Jupiter and Saturn cast shadows, as did the Milky Way. The "Dark Horse" section of dark nebulae in the Milky way's bulge looked dark and painted on as if with a paintbrush. M11 was a bright, naked-eye, spot in the Scutum starcloud, and most meteors were so bright as to be painful and deleterious to one's night vision. On that night, my 8" SCT (standard coatings) reached magnitude 15.6 in a couple test clusters.

I don't expect to see many more nights that dark in the rest of my life.
Tom Polakis said to me "It's as dark as it gets on Earth." And since he'd travelled to many of the world's darkest places, I took him at his word.
I've never seen it as dark since.

A new conversion formula of SQM measurements to NELM means my recent measurement of 21.69 translates to magnitude 6.9 at the zenith. That formula says a magnitude 22.0 sky (the faintest it can get on Earth) would be 7.06 NELM.

If people have legitimately seen stars to magnitude 8, and I have no reason to doubt that some eagle-eyed individuals have, then the formula needs to be revised. In that case, my recent measurement of 21.69 translates to magnitude 7.85 NELM.

I have no hope of ever seeing a star that faint with my naked eye, but that should have been the limit on that night.

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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie