Astronomers Measure the Background Brightness of the Night sky Across the World. Canary Islands are the Darkest in the Survey

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Astronomers Measure the Background Brightness of the Night sky Across the World. Canary Islands are the Darkest in the Survey

In the rich world, it is becoming increasingly rare to be able to look up into a clear, dark sky. Authors, artists, and even scientists have raised concerns about what our lack of daily exposure to a dark night sky could mean for our psyche and our sense of place in the universe. Now a team in 44 locations around the world has collected photometric data to quantify how dark the night sky actually is in different places around the world. So where was the darkest place measured? The canary islands.

It just so happens that the lead researcher on the project, Dr. Miguel Alarcón, comes from this group of islands off the west coast of Africa. The paper he and his colleagues had written, soon to be published in the Astronomical Journal, used a series of photometers called TESS (not to be confused with the Transiting Exoplanet Survey Satellite) to get a baseline for the darkness of the night sky around the world.

Example of a standardized TESS photometer.
Photo credit: TESS / Stars4all

The team collected 11 million data points from locations to Namibia, Australia and the USA. While this didn’t include some more popular astronomical locations like the Antarctic highlands, it was a good sample of various conditions. As mentioned above, the Canary Islands had the lowest background light of any area studied. Only about 2% of the night light in the sky comes from artificial light at the Roque de los Muchachos observatory in Garafia.

However, there are other natural sources of light pollution that affect different regions differently. The moon and the Milky Way are part of the standard of the night sky and undoubtedly contribute to its natural brightness. However, there are other, more variable sources that were monitored in this study. This includes a glow in the upper atmosphere caused by a combination of factors such as the solar cycle, geographic location, and time of year.

Example of different types of light sources in the night sky, including the counter-light effect.Example of different types of light sources in the night sky, including the counter-light effect.
Photo credit: Juan Carlos Casado

Another source is the “counter-glow” or the anti-sun point, directly opposite the sun in the night sky. This can only be seen in extremely dark places, and the Institute of Astronomy in the Canary Islands (IAC) is one of them.

Just because it has one of the darkest skies doesn’t mean it’s the best place for all observation. Other factors such as atmospheric vision and temperature changes can cause observation problems. The real downside to this research is that if you really want to see the night sky like our ancestors did, it may be worth taking a trip to some of the islands off the coast of Africa.

Vertical panorama showing the night sky over the Canary Islands. Vertical panorama showing the night sky over the Canary Islands.
Photo credit: Juan Carlos Casado

Learn more:
IAC – The natural brightness of the night sky
UT – Most of the light pollution doesn’t come from street lights
UT – See light pollution in action

Mission statement:
Image of the Roque de los Muchachos observatory in the Canary Islands (upper part) and the La Silla observatory in Chile in the lower part. The composition makes the Milky Way appear circular.
Photo credit: Juan Carlos Casado & Petr Horálek

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