Understanding the meaning of light pollution in astronomy

People may wonder why observatories are often located miles from the nearest towns and sometimes in remote places. After all, this increases the cost of building the structure to house the telescope and makes it more difficult to set the telescope up. However, there is a good reason this is done: Light pollution.


When people think of pollution, filth in water, on the land or in the air often comes to mind. To a person who isn’t an astronomy enthusiast or an actual astronomer, there could be a tendency to be incredulous if someone said that light also pollutes.

In this case however, the pollution doesn’t necessarily foul the environment though some scientists may not entirely agree with such an assessment.


Part of the confusion may be due to a misunderstanding of what telescopes actually do. A lot of people probably think of telescopes as merely a magnifying device.

This equipment certainly does this. Still it does much more. Distant stars or even planets don’t produce a great deal of light. Just magnifying the object means that the object becomes dimmer because less light from the planet or star is reaching our eyes. To counter this, one of the main purposes of a telescope is to gather more light from whatever is being viewed. 


Most people are probably acquainted with many forms of interference. For instance, going to a movie theater and trying to watch a movie when everyone else is talking makes it extremely difficult to hear what is being said in the movie. This is a form of sound pollution or interference. In much the same way, a telescope that is situated near city lights experiences light pollution because the light from the city interferes with the telescope’s ability to gather light from distant objects.

More personal

Light pollution has an impact on more than only telescopes. People who are far from any house or town may notice that they can see far more stars than they can when they are viewing the sky from their own backyards. This is also an instance of light pollution.

Light reaching the eyes from nearby sources overwhelms the much dimmer light of the stars. The result is that the brighter stars can be seen but those that aren’t as brilliant normally can’t be. 


There are also degrees of light pollution. A person sitting in camp, near a campfire, will likely see more stars than someone standing in a brightly lit street, even if the air quality is similar between the two sites. There is light pollution in both cases, however it is greater as the light becomes brighter near the observer. The person would probably see even more stars if they were away from any light source.

Air conditions

Some air conditions increase light pollution. The culprit is usually fine suspended particles that reflect the light in the area. For instance, smoke from forest fires can intensify the pollution, sometimes even causing light pollution from light reflected from distant sources. As put by an astronomer at a small observatory in Oregon, “We are located many miles from the nearest town, yet during the forest fire season, we figure on losing several nights of observing time due to smoke. It really isn’t the smoke that is the problem. Rather, the smoke reflects the light from town. We have to shut down due to the pollution and it is something we can’t control.”

At first glance, it would seem that light pollution would be easy to define. However, it is actually quite a bit more complex than most people might imagine. Explaining what it is, to be done properly, necessitates explaining how it has an impact and ways that it can be intensified.