Talk:Bortle scale

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The SQM column is way off

Where I live, rural skies are something like 21.4 SQM, and dark sky sites at national parks only surpass 21.7 if it's exceptionally transparent (as measured by my SQM-L device). The current SQM ranges don't match up with the cited Nomogram. — Preceding unsigned comment added by 174.116.183.78 (talk) 20:36, 25 May 2022 (UTC)[reply]

Average (or is it median?) unpolluted sea level cloudless full night is about 21.6 at the zenith or 80 nanolamberts, at least with no aurora, the same thing at solar minimum is about 60 nanolamberts. Sagittarian Milky Way (talk) 22:04, 25 May 2022 (UTC)[reply]

Bortle 1 SQM discussion

I recommend changing the Bortle 1 SQM column from 21.75 - 22 to > 21.75. I have measured sqm fainter than 22 on exceptional nights, including not at the zenith. DrRogerNClark (talk) 19:22, 7 June 2023 (UTC)[reply]

zodiacal light & zodiacal band bullet points

I quickly added a link in Bortle Class 1 to point the bullet item "zodiacal band" to "zodiacal light".

I then wondered if those two bullet points, the 1st and 3rd, (zodiacal light and zodiacal band) should be merged into a single bullet like "the zodiacal band and the zodiacal light is visible and colorful"

I would have made this change, but wanted to ask if this is something agreeable, or if they do need to be two points as is, or there is a better way to phrase a single bullet point similar to my example. AreThree (talk) 23:51, 2 January 2024 (UTC)[reply]

Northern hemisphere bias in scale description

While it's understandable that the scale has a northern hemisphere bias, given its original publication in a US astronomy magazine, the description of the scale on Wikipedia needs to be updated to be applicable globally. I've added a globalise section template as I don't think the fix here is to simply change the seasons to their equivalent months or year quarters, as would be done in most cases where a season is given as a timeframe from a northern perspective. There is additional ambiguity in this case as different parts of the night sky are visible from the two hemispheres, and what is visible in the northern summer sky is not the same as what is visible in the southern winter sky. The section therefore needs updating by someone more familiar with the subject to ensure its global application. Terovian (talk) 06:10, 8 August 2025 (UTC)[reply]

We explicitly introduce "Bortle's descriptions of the classes are summarized in the table." The table isn't globalised because it can't be—Bortle didn't create it that way, and we can't go back and rewrite quarter-century-old primary source material.

Looking a little more closely, it also appears that someone bolted on a an extra column of nominal NELM SQM values which also weren't part of Bortle's publication, and probably don't belong in the table as presented. (Actually, that column should be removed anyway, because the source that is cited does not contain the numbers that are added to our article.)

Perhaps there's a place for a separate section in our article on extensions, expansions, and interpretations of the Bortle scale, that might address the way the scale has been modified, updated, extended, or localised for different purposes since its original publication...? I would hope to see good-quality sources for any such additions, though; that sort of section can become a dumping ground or linkfarm for everyone's favourite blog posts.... TenOfAllTrades(talk) 11:38, 8 August 2025 (UTC) (minor edit to refer to correct added column TenOfAllTrades(talk) 15:02, 8 August 2025 (UTC))[reply]

I sympathize that the scale isn't that helpful for the southern hemisphere, but I concur with TenOfAllTrades that that's not a solveable problem. I searched for a while for RS that describe the scale with southern hemisphere objects, but came up empty – this^[1] is the closest I could find, suggesting the scale sees professional usage for the southern sky anyway. I don't personally believe the bias template is necessary.

A recurring comment on this talk page is objecting to the SQM column in the table. I think it should remain, and that it's helpful that the table compares among the main different methods of measuring NSB.

Perhaps changing the table's introductory sentence to something like "The classes of the Bortle scale are summarized in the table" is all that's needed, to make clear that the table includes info not found in the original publication.

The graphic on the "sky brightness nomogram" source corresponds to the SQM numbers in the table. I think the existing source is good enough, but a similar source would be fine too. This^[2] RS makes clear that SQM, NELM, and the Bortle scale are all correlated, just not extremely tightly (r = 0.76 for SQM vs Bortle), and it should probably be worked into the article somewhere.

RN Andy in Boise (talk) 18:41, 11 August 2025 (UTC) RN Andy in Boise (talk) 18:41, 11 August 2025 (UTC)[reply]

References

1. Riyadi, Slamat (2023-12-15), Star Trail in the Southern Hemisphere with Bortle 4 Scale Light Pollution, doi:10.5281/zenodo.10356977, retrieved 2025-08-11
2. Hung, Li-Wei (2022-03-09). "Identifying distinct metrics for assessing night sky brightness". Monthly Notices of the Royal Astronomical Society. 511 (4): 5683–5688. doi:10.1093/mnras/stab2662. ISSN 0035-8711.