The multiplication of satellites threatens astronomy

On June 21, a huge beam of lights crossed the sky from the Extremaduran town of Trevejo. The alleged UFOs turned out to be artificial satellites of ‘Starlink’, a project promoted by tycoon Elon Musk. The event caused concern in Extremadura, a community that has committed to astronomical tourism.

Musk’s company has permission to launch up to 12,000 satellites. The hundreds already in orbit are noticeable. This July, a photographer released a image of the Neowise kite, crossed by dozens of luminous traces of ‘Starlink’ satellites. In November 2019, the Calar Alto Observatory (Almería) captured the same “string of pearls”. “The passage of these satellites can ruin an observation,” he says. Jorge Nunez, Professor of Astronomy at the University of Barcelona.

Núñez is part of a workgroup created by the Spanish Astronomical Society (SEA) to tackle the problem. Starlink is just one of several projects from “satellite constellations”, like ‘Kuiper’ or ‘OneWeb’. The International Astronomy Union consider these projects “worrisome”.

The number of projected satellites exceeds the number of objects sent into space in all of history (about 9.000, according to the United Nations). “On any observation afternoon you see satellites, but when we have ten times more the problem will be ten times bigger,” he says. David Galadí, astronomer at the Calar Alto Observatory and member of the SEA group.

Internet for remote areas

The miniaturization and cheaper of technology has allowed a new strategy (new space) based on launching many small devices. Constellations are made of microsatellites They weigh a few hundred kilograms and are about a meter wide.

With this technology, you can provide internet connection to remote areas where fiber optics does not reach, penetrating markets such as Africa, China or India.

“There are communication, food or resource problems, which are costly to solve from the ground and can be solved from orbit,” he explains. Gerardo Richarde, co-founder of the company Satellogic, which plans to launch 300 microsatellites to monitor agricultural fields, natural areas and infrastructure.

Not all satellites have to be visible. A simulation The European Southern Observatory (ESO) with 25,000 satellites has concluded that only about 300 would be above the visible horizon and most would have a dim glow.

In addition, the devices are seen only at dusk or dawn, before leaving the cone of sunlight. “Pearl strings” are very bright shortly after launch. When they reach their final orbit, their light is less intense. “The claim that there will be more satellites than stars in heaven it’s not true “, ditch Andrew Williams, co-author of the ESO study.

However, that does not solve the problem. The final orbits are usually quite close to the Earth’s surface. For this reason, they will continue to be noted in especially dark places And in the astronomical photographs.

“The world has to wonder what right a company has change the sky permanently“reflects Williams.” Humanity has the right to enjoy the natural landscape as part of its heritage“, affirms Galadí.

Science would also be affected. In some observatories, up to a third of the images should be shot of dusk. “Science will be lost: it may happen that they try to observe a signal and cannot,” observes Galadí.

Negotiation with Musk

Musk has been sensitive to the problem and his company is experimenting with a system (DarkSat) to darken the satellites. It is not easy, because black overheats appliances.

For their part, astronomers ask for more transparency on launches and trajectories, to turn off your telescopes in time and to put in place automatic systems that remove the traces of the satellites from the images, when possible.

However, these measures can subtract hours of observation and add hours of image processing each night, with significant costs for science. “Who will pay for these efforts?Williams wonders.

So far, no one has argued that companies pay something. There are also no international agreements that regulate the number of satellites or their luminosity.

“Try to have legislation establish prohibitions it is impossible. If the United States did, companies would go to China. And vice versa, “notes Núñez. Given this scenario, the United States Astronomical Association has chosen to sit down negotiate with Musk, waiting for good practices to be established.

However, there are those who are not satisfied. “It is intended that the Internet reaches Africa and Asia through the hands of foreign countries and foreign companies, outside the control of the user population. It is a model deeply unfair and without democratic control, “concludes Galadí.

The impacts on science

Wide field observatory

These devices photograph large portions of the sky, looking for supernova explosions, range ray emissions, or collisions that generate gravitational waves. The largest observatory of its kind, the Vera Rubin being built in the United States, would be almost out of the game. The light from so many satellites would saturate a third of his photographs at dusk.


Telescopes targeting small areas of the sky would be less affected, because they could be turned off when a satellite passes on its plot. However, in major observatories such as ESO’s Very Large Telescipe, 3% of the dusk images would have to be shot.


The impact on observatories that capture radio waves rather than light is yet to be studied. In this case, the signals from the satellites would affect the whole night. “In theory, there are frequencies reserved for astronomy, but satellites emit in very close bands and sometimes invade them,” observes Galadí.


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