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The night sky is getting brighter

The night sky is getting brighter

The night sky is slightly polluted due to satellites and other things that people throw into space.

Researchers write this in the journal Monthly Notices of the Royal Astronomical Society: Letters. Satellites, space debris, and other things orbiting the Earth have been found to literally light up the night sky. Researchers estimate that in some places, the night sky is 10 percent brighter than it would be in the absence of these objects. In many cases, satellites alone cause an area to be classified as “light polluted” by the official criteria.

Telescopes against our eyes
This is not the first time that researchers have investigated the effect of satellites and other objects orbiting the Earth on the night sky. For example, there has already been a lot of interest in satellite towers under construction, which will eventually have thousands or even tens of thousands of satellites. These satellites are already regularly present in telescope images – often as bright points or lines – thus impeding astronomers’ observations.

But for the new study, the researchers haven’t looked at how satellites (permanently) alter the viewpoint of the telescopes. Instead, they examined how all of the objects in orbit – from satellites to space debris – altered the night sky for us as observers. Our eyes aren’t sharp enough – just like telescopes – to spot and disturb individual satellites. But we can see the combined effect of all of these things on the brightness of the night sky.

Researcher John Barentin explains: “When the angle between the sun and the space object and the observer on the Earth is completely correct, the space object intercepts the sunlight and reflects it from the night side of the Earth.” “We can see large objects that intercept large amounts of sunlight (such as the International Space Station, Ed) as a bright spot in the sky. But there are also many, many smaller objects (in Earth orbit, ED); some of them are only a few centimeters in size or Millimeters. Although an observer cannot perceive them as separate sources of light, they contribute to the light that your eye receives. ” The result of all these light sources – large and small – together is a brighter night sky (see box).

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The night sky is never completely black. “In addition to the light from the universe, the Earth’s atmosphere also shines very weakly, because chemical reactions occur so high above the planet.” So the night sky is always somewhat “bright”. So the light reflected by satellites and space debris is above that.

In this study, scientists examined how bright the night sky is now due to satellites and space debris. “Since it was never studied, we were not sure what to expect,” says Barentin. “We were surprised that the effect was so impressive; much larger than we thought. We carefully reviewed our model and our calculations on it to make sure that we did not make a mistake. But after these checks, the result was that space objects ensure that the night sky becomes 10 percent brighter. At least because of the natural light sources in the earth’s atmosphere and outside it, “it is.


Before the huge constellations
This estimate is based on a model (see box), which in turn is based on the most recent data the researchers had on the number of objects in orbit and the size of these objects. However, this data dates back to the period before the construction of massive satellite constellations, such as Starlink (from SpaceX), began. Meanwhile, SpaceX alone has launched about 1,500 satellites. But its effect on the night sky has not yet been taken into account. In fact, we reveal the condition it was in before the era of the massive space constellations began. This is why we also argue that you should see an increase in the brightness of the night sky by 10 percent as a minimum; The night sky will be brighter in the years to come. ”

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The researchers used a model to obtain an image of the effect of satellites and space debris on the night sky. Based on that data, the model predicts that the night sky became 10% lighter before the massive constellations were created. “We have not yet been able to verify the model’s predictions through observations,” says Barentin. “This is practically impossible from the Earth’s surface, due to the natural light sources in the atmosphere.” To verify the results, observations must actually be made from space. One option would be to do so from the International Space Station. We are now investigating this possibility. “

If you look at the starry sky with the naked eye, you will not immediately notice that the night sky has become 10 percent brighter. Things will change as the night sky gets brighter. Glowing star clouds in the Milky Way, which you can still see well at a great distance from light-polluted cities, may be hidden from view. “In a truly ‘pure’ place (in other words: barely polluted with light) that place, you can see as many as 6,000 stars scattered across the night sky,” says Barentin. “If the night sky is 10% brighter, that number is slightly smaller. But if the night sky becomes 50% brighter, it decreases by 1000. This is important.”

The upper limit cannot be expected
It is difficult to estimate how bright the night sky will be. “One of the main uncertainties is the effect of space debris,” Parenten notes. As more and more objects are placed in Earth orbit, you can expect more and more collisions between objects in the future. “But we don’t have a good idea yet about how many times collisions would occur if more satellites orbiting the Earth were to increase.”

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We hope you do not reach that limit. But nothing is stopping companies and organizations from putting things into orbit at the moment. There are no international or national laws prohibiting or restricting this. “Everything basically boils down to the question: Is the space owned by all of us, or is the space actually owned by those who use it? No international agreements have been reached on this subject yet.” And so companies like SpaceX, Amazon, and OneWeb continue to boldly build their huge clusters. “As long as states and companies are allowed to put things – without many restrictions – in orbit around the Earth, it is hard to imagine that the situation we describe in our research will improve. We have worked for a long time to limit the impact of artificial light sources on Earth in the night sky. These efforts are due to the high light sources above our planet which are difficult to address. I do not want to say that it is too late to change the situation, but with each new satellite launch it becomes more difficult. “

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