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The Bortle Scale

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 Class 9, inner-city skies.

(Source: Wikipedia)

Astronomy Photo of the Day: 6/26/15 — The Milky Way Meets the Grand Canyon

The light from thousands of stars shine in this stunning image in which the Milky Way meets the Grand Canyon. Since it is rather secluded, and far away from man-made light pollution, it is counted among an increasingly small number of places on Earth with pristine views of our galaxy (a class 1 sky, per the Bortle Dark-Sky Scale).

This image, which was taken by David Lane, features Bright Angel Point, located on the norther rim of the Grand Canyon—where one is treated to panoramic views of the surrounding terrain.

Sources & Resources: http://bit.ly/1JnzIAA

Image Credit: David Lane Photography

There’s a statistic that I quote, which is that eight of every ten kids born in the United States today will never experience a sky dark enough to see the Milky Way. The Milky Way becomes visible at 3 or 4 on the Bortle scale. That’s not even down to a 1. One is pretty stringent. I’ve been in some really dark places that might not have qualified as a 1, just because there was a glow of a city way off in the distance, on the horizon. You can’t have any signs of artificial light to qualify as a Bortle Class 1.

A Bortle Class 1 is so dark that it’s bright. That’s the great thing-the darker it gets, if it’s clear, the brighter the night is. That’s something we never see either, because it’s so artificially bright in all the places we live. We never see the natural light of the night sky.

-Kottke

The Bortle scale was originally published in Sky & Telescope magazine in 2001. It classifies the darkness of skies from point of view of an astronomer, ranging from 1 (“an observer’s Nirvana!”) to 9, in which “the only celestial objects that really provide pleasing telescopic views are the Moon, the planets, and a few of the brightest star clusters.” This illustration of the scale comes via Stellarium.

Light Pollution Simulation / Bortle Scale

Medical research on the effects of excessive light on the human body suggests that a variety of adverse health effects may be caused by light pollution or excessive light exposure, and some lighting design textbooks use human health as an explicit criterion for proper interior lighting. Health effects of over-illumination or improper spectral composition of light may include: increased headache incidence, worker fatigue, medically defined stress, decrease in sexual function and increase in anxiety.Light pollution poses a serious threat in particular to nocturnal wildlife, having negative impacts on plant and animal physiology. It can confuse animal navigation, alter competitive interactions, change predator-prey relations, and cause physiological harm. The rhythm of life is orchestrated by the natural diurnal patterns of light and dark, so disruption to these patterns impacts the ecological dynamics.Astronomy, both amateur and professional, is very sensitive to light pollution. The night sky viewed from a city bears no resemblance to what can be seen from dark skies. Skyglow (the scattering of light in the atmosphere) reduces the contrast between stars and galaxies and the sky itself, making it much harder to see fainter objects. (wiki)