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Bortle scale

Representation of the Bortle scale

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. Amateur astronomer John E. Bortle created the scale and published it in the February 2001 edition of Sky & Telescope magazine to help skywatchers 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 2014 research.[2][why?] The table summarizes Bortle's descriptions of the classes. For some classes, there can be drastic differences from one class to the next, e.g, Bortle 4 to 5.[why?]

Table of dark-sky classifications

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

In this 10-second exposure photo, facing south toward Sagittarius, light pollution obscures the stars and faintly visible Milky Way in the suburban night sky over Southern California.
In this 4 minutes exposure photo, facing up the sky pointing directly up on Kappa Ophiuchi in the constellation of Ophiuchus. With other constellations such as Scutum, Hercules, Corona Borealis, Scorpius, Bootes, Libra, a hint of Lyra star (Vega) and a hint of Sagittarius star (Polis) and Messier objects such as M16 and M24. Light pollution is small, doesn't obscure the stars and visible Milky Way (at the corner) in the exurban night sky over Kepala Batas, Kedah. The light pollution here is class 3 in the Bortle scale.

References

  1. ^ Bortle, John E. (February 2001). "Gauging Light Pollution: The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 2020-05-29.
  2. ^ 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.
  3. ^ "Dark Skies Awareness". Archived from the original on 2020-11-12. Retrieved 2016-02-18.
  4. ^ "Days N' Daze – Nine on the Bortle Lyrics". Genius Lyrics.

External links

Wikimedia Commons has media related to Light pollution.