When we refer to astronomy, we hear about stars, planets, constellations. But where are they? They've been disappearing from our sight because of light pollution.

What is light pollution?
It is any adverse effect produced by artificial light, resulting in the decrease in visibility we have of the night sky. In general, it is all the light produced by lamps and lighting in cities, which, because of the inadequate way in which they have been installed, emit light in all directions, causing us not to see the light that reaches us from the stars and stellar objects, when we are in a large city.

Photo of a suburb in the city of Toronto, before and after a blackout

For science and astronomy, the impact has been dramatic. Astronomers are required to make observations of very faintly glowing star objects that can only be seen with large telescopes in places far from the air pollution and glare of city lights. For example, scientists interested in how the universe formed can study the light from galaxies and quasars that are at huge distances from Earth. These images offer information about the far corners of the universe, helping us to understand even how our planet was formed. Even after traveling countless light years, the light from these objects can be lost at the end of their journey in the artificial glow of our own sky.

For us amateur astronomers, it is necessary to get away from the city for a couple of hours in order to make observations. To give an example: a popular place, near Guadalajara, México, is a property that is located 5 minutes before arriving at Atemajac de Brizuela, on the way to Tapalpa, in which, it is possible to observe a beautiful sky, without having to go too far. But if we want to improve our possibilities of a better observation, and we are more demanding, it would be necessary to go to desert places, of dry climates, far from any artificial light.


For many people in North America and Europe, the night sky is no longer black, or even dark. Instead, almost starless, they see only an orange-yellow glow, illuminated by poorly designed decorations and the light of excess human activity. Satellite images of Earth no longer show the night side of our planet as dark. For some people born in the 1980s or later, the only celestial object they have ever seen in the night sky is the Moon.

THERE ARE NO DARK SKIES IN CENTRAL EUROPE, where the glow of a city blends with that of its neighbour. Only sparsely populated populations, and relatively poor ones, have dark skies.

What is the origin of light pollution ?
This type of pollution is mostly caused by the inefficient use of public lighting. There are street lamps in cities which emit light in all directions, instead of lighting only necessary areas. The urban brightness of the sky is the result of the light that escapes (as a whole) from the cities and is dispersed by the atmosphere thus increasing the levels of natural brightness of the sky.

Another very common source of pollution is the lights from billboards, which are installed at the bottom of the billboard, instead of the top, causing all the light to be directed towards the sky instead of towards the ground.

To avoid the adverse effects of faulty lighting, it is necessary to carefully choose the type of lamp, type of device (light flow diagram) and position it properly to avoid misdirected light.

In summary, there are luminaires that spend and emit more light than is needed, generating a waste of energy and poor lighting, and above all, that we can not observe the wonders of the night sky.

International Dark-Sky Association (IDA)
There is an international association, the International Dark Sky Association (IDA), which aims to preserve the darkness of the night sky by making responsible use of outdoor lighting. This organization also promotes standards among manufacturers of lighting equipment so that they are manufactured more efficiently and reduce visual pollution.

Success stories
Let's talk about the case of Flagstaff, Arizona, in the United States. It is a small town located between the Colorado Plain and Mount San Francisco. The city of Flagstaff has contributed so many times to astronomy that the city has an asteroid, 2118 Flagstaff. And thanks to the commitment of its astronomers, it was honored with the title of "International Dark Sky City" on October 24, 2001. Efforts to preserve the darkness of the night sky date back to 1958 when city lights were removed because they interfered with the work of astronomers. In 1973, Flagstaff passed an order to businesses asking them to keep the light low. In 1989, the city placed a set of restrictions on the number of lumens used per acre in each area, based on proximity to the observatories. These efforts have reduced visual pollution.


External Links
International Dark-Sky Association