Light from satellites is sabotaging our search for dim galaxies and dark matter

Light pollution has become a headache for our astronomers.
Rupendra Brahambhatt
Planet Earth
Planet Earth


A report from U.S. Government Accountability Office (GAO) reveals that there are nearly 5,500 man-made satellites presently orbiting the Earth. It is estimated that by 2030, our planet will be surrounded by 58,000 more satellites. So is this a good or a bad thing?

Well, it’s kind of both. Artificial satellites provide us with useful information on weather and climate patterns. They help us stay connected by facilitating our telephone calls and internet signals. Plus, our TV and radio broadcasts are also made possible by satellites.

From helping us share our location via GPS to keeping an eye on natural disasters, satellites perform numerous tasks that are of great value to us. 

However, at the same time, they are super expensive, contribute to the increasing space junk (when they become inactive), and according to a recent study, they are also responsible for the increasing light pollution in space.

Light pollution? What the heck is that? 

Well, you may have heard enough about air, water, and land pollution on Earth. However, outer space does not have any of these three elements, but it does have light and darkness. Every satellite has its own light that lits up the skyline or space around it.  

There are thousands of active satellites orbiting our planet at present. The artificial light from all these satellites provides the night sky with an additional glow. This extra glow or light makes it difficult for astronomers on Earth to find and study distant objects in space, such as dim galaxies.

Astronomers believe that the faint and low-light areas in space may have important hints related to dark matter and various other mysterious space phenomena. They even employ some of the biggest and most advanced telescopes for this purpose. Moreover, the artificial glow also leads to errors in data collected by space observatories. 

However, the light pollution or extra glow in the skyline because of the satellites serves as one of the biggest hindrances in their search for dim and dark space objects. “It occurred to me there could be a whole universe up there of hidden galaxies, just a little dimmer than those we can detect from Earth,” Emeritus professor at Cardiff University, Michael Disney, told Discover Magazine in a 2019 interview.  

You can relate to the problem astronomers face due to light pollution with the help of a simple daily-life example. Imagine you are out on a sunny day, and your phone’s brightness is at the minimum level. In order to watch or read anything on your phone, you’d have to increase the brightness to overcome the glow from the Sun, right? 

Similarly, the collective glow from different satellites in Earth’s orbit becomes so powerful at night that it washes away any low-intensity light coming from a dim object before it reaches an astronomer’s eye through the telescope. Of course, astronomers can’t set the brightness levels of a dim object in space, as you can do with your phone screen.

Light pollution has already crossed the limit

Authors of the current study claim that it’s not just the light from active satellites that is of concern. The cloud of thousands of inactive satellites and various other types of space junk that’s currently floating around Earth also contributes to light pollution. 

Since these objects are located at great heights from our planet, they are able to experience and reflect sunlight even in the night sky.

Explaining this in detail, the authors wrote, “We refer to both satellites and space debris here as ‘space objects.’ The orbital altitudes of space objects range from a few hundred kilometers to beyond the 35 786-km height defining geosynchronous orbits. At such altitudes, space objects remain directly illuminated by sunlight as seen from the night side of the Earth.” 

They further added, “Consequently, they appear in images obtained with ground-based telescopes as streaks of various lengths. Because the streaks are often comparable to or brighter than objects of astrophysical interest, their presence tends to compromise astronomical data and poses the threat of irretrievable loss of information.”

The International Astronomical Union recommends that light pollution should not be more than 10 percent of the total glow of a natural night sky. The researchers claim that the luminance from space objects orbiting Earth has already reached the 10 percent mark, and these figures are likely to get worse with more satellites entering Earth’s orbit in the coming years.  

Apart from space agencies like NASA and ESA, private players like SpaceX and Blue Origin also have ambitious plans to launch numerous satellites into Earth’s orbit in 2023. Many of these missions are important for improving our understanding of space and bringing advancement in communication, navigation, and various other technologies.

Therefore, an effective strategy against light pollution is the need of the hour. Hopefully, the current research work will bring people’s attention to this growing problem and encourage scientists and space agencies to come up with a solution. 

The study is published in the journal Monthly Notices of the Royal Astronomical Society.

Study Abstract:

The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite ‘mega-constellations’ in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached ∼20 μcd m−2, which amounts to an approximately 10 percent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories.

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