Bortle scale: Difference between revisions
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The '''Bortle dark-sky scale''' (usually referred to as simply the '''Bortle scale''') is a nine-level numeric scale that measures the [[night sky]]'s [[sky brightness|brightness]] of a particular location. It quantifies the [[astronomy|astronomical]] observability of [[celestial objects]] and the interference caused by [[light pollution]]. [[John E. Bortle]] created the scale and published it in the February 2001 edition of ''[[Sky & Telescope]]'' magazine to help [[amateur astronomers]] evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, through to Class 9, inner-city skies. It gives several criteria for each level beyond [[naked-eye]] [[limiting magnitude]] (NELM).<ref>{{cite web|url=https://skyandtelescope.org/astronomy-resources/light-pollution-and-astronomy-the-bortle-dark-sky-scale/|title=Gauging Light Pollution: The Bortle Dark-Sky Scale|last=Bortle|first=John E.|date=February 2001|work=[[Sky & Telescope]]|publisher=Sky Publishing Corporation|access-date=2020-05-29}}</ref> The accuracy and utility of the scale have been questioned in recent research.<ref>{{cite journal |author=Crumey, Andrew |year=2014 |title=Human Contrast Threshold and Astronomical Visibility|journal=Monthly Notices of the Royal Astronomical Society |volume=442 |issue=3 |pages=2600–2619 |doi=10.1093/mnras/stu992 |arxiv=1405.4209 |bibcode=2014MNRAS.442.2600C}}</ref> The table below summarizes Bortle's descriptions of the classes. For some classes, there can be very drastic differences from one class to the next, e.g, Bortle 4 to 5. |
The '''Bortle dark-sky scale''' (usually referred to as simply the '''Bortle scale''') is a nine-level numeric scale that measures the [[night sky]]'s [[sky brightness|brightness]] of a particular location. It quantifies the [[astronomy|astronomical]] observability of [[celestial objects]] and the interference caused by [[light pollution]]. [[John E. Bortle]] created the scale and published it in the February 2001 edition of ''[[Sky & Telescope]]'' magazine to help [[amateur astronomers]] evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, through to Class 9, inner-city skies. It gives several criteria for each level beyond [[naked-eye]] [[limiting magnitude]] (NELM).<ref>{{cite web|url=https://skyandtelescope.org/astronomy-resources/light-pollution-and-astronomy-the-bortle-dark-sky-scale/|title=Gauging Light Pollution: The Bortle Dark-Sky Scale|last=Bortle|first=John E.|date=February 2001|work=[[Sky & Telescope]]|publisher=Sky Publishing Corporation|access-date=2020-05-29}}</ref> The accuracy and utility of the scale have been questioned in recent research.<ref>{{cite journal |author=Crumey, Andrew |year=2014 |title=Human Contrast Threshold and Astronomical Visibility|journal=Monthly Notices of the Royal Astronomical Society |volume=442 |issue=3 |pages=2600–2619 |doi=10.1093/mnras/stu992 |arxiv=1405.4209 |bibcode=2014MNRAS.442.2600C}}</ref> The table below summarizes Bortle's descriptions of the classes. For some classes, there can be very drastic differences from one class to the next, e.g, Bortle 4 to 5. |
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== Table of dark-sky classifications == |
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Revision as of 17:42, 21 December 2023
The Bortle dark-sky scale (usually referred to as simply the Bortle scale) is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. John E. Bortle created the scale and published it in the February 2001 edition of Sky & Telescope magazine to help amateur astronomers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, through to Class 9, inner-city skies. It gives several criteria for each level beyond naked-eye limiting magnitude (NELM).[1] The accuracy and utility of the scale have been questioned in recent research.[2] The table below summarizes Bortle's descriptions of the classes. For some classes, there can be very drastic differences from one class to the next, e.g, Bortle 4 to 5.
Table of dark-sky classifications
Class | Title | NELM | Approx. SQM[3] mag/arcsec2 |
Description |
---|---|---|---|---|
1 | Excellent dark-sky site |
7.6–8.0 | 21.75~ |
|
2 | Typical truly dark site |
7.1–7.5 | 21.6–21.75 |
|
3 | Rural sky | 6.6–7.0 | 21.3–21.6 |
|
4 | Brighter rural | 6.3–6.5 | 20.8–21.3 |
|
4.5 | Semi-Suburban/Transition sky | 6.1–6.3 | 20.3–20.8 |
|
5 | Suburban sky | 5.6–6.0 | 19.25–20.3 |
|
6 | Bright suburban sky |
5.1–5.5 | 18.5–19.25 |
|
7 | Suburban/urban transition |
4.6–5.0 | 18.00–18.5 |
|
8 | City sky | 4.1–4.5 | <18.00 |
|
9 | Inner-city sky | 4.0 |
|
In popular culture
The band Days N' Daze referenced the scale in the title and lyrics of their song Nine on the Bortle.[4]
See also
- 4673 Bortle
- Amateur astronomy
- Dark-sky movement
- The End of Night (book)
- International Dark-Sky Association (IDA)
- Light pollution
- Night sky
- Sky brightness
- Sky & Telescope (S&T)
References
- ^ Bortle, John E. (February 2001). "Gauging Light Pollution: The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 2020-05-29.
- ^ Crumey, Andrew (2014). "Human Contrast Threshold and Astronomical Visibility". Monthly Notices of the Royal Astronomical Society. 442 (3): 2600–2619. arXiv:1405.4209. Bibcode:2014MNRAS.442.2600C. doi:10.1093/mnras/stu992.
- ^ "Dark Skies Awareness". Archived from the original on 2020-11-12. Retrieved 2016-02-18.
- ^ "Days N' Daze – Nine on the Bortle Lyrics". Genius Lyrics.