Constellations of satellites pose a growing threat to astronomy

A group of star-linked satellites (longitudinally parallel curves) pass over carson National Forest In New Mexico, USA. Image credit: M. Lewinsky (CC BY 2.0)

Three years ago, SpaceX launched the first Starlink Starlink internet communications satellites, raising concerns among astronomers about the streaks the satellites left on photos of the night sky. Since then, many other “starlinks” have been launched, and today more than 2,300 “starlinks” orbit the earth, accounting for almost half of all operating satellites.

However, there is growing evidence that these “starlinks” will cause considerable interference to astronomical observatories and other astronomical observers around the world, and satellite companies have not yet found a solution, and tens of thousands of new satellites may be launched in the next few years.

Since the launch of the first Starlink, astronomers have begun to organize global forces to respond. After a series of international studies over the past two years, the International Astronomical Union (IAU) has set up a center to protect dark and quiet skies from satellite constellations to coordinate how to reduce the impact of satellites crossing the sky for astronomers, policymakers, satellite operators and others.

A recent study published in the Journal of Astronomy suggests that future satellite constellations will be most pronounced on summer nights around 50° south and 50° north, where many European and Canadian astronomical facilities are built. If SpaceX and other companies launch the planned 65,000 satellites, there will be bright spots of light in the night sky at these latitudes around the summer solstice, the study said. In the hours around sunrise and sunset, about one out of every 14 stars visible to the naked eye is a satellite.

Astronomical observatories that study vast skies will be most affected. The Zwicky Transient Facility (ZTF) in Palomar Mountain, California, observed 18 percent of satellite stripes in images taken at dusk in August 2021. Przemek Mróz, an astronomer at the University of Warsaw in Poland, points out that the number will rise as the number of satellites increases. He conducted a preliminary analysis of data from the April 2022 ZTF and found that the satellite’s stripes affected about 20 to 25 percent of the dusk images.

Mróz said that so far, many of ZTF’s measurements have not been destroyed by satellite stripes, in part because its image processing methods can detect and mask satellite trajectories. But other observatories face greater challenges, notably the Vera Rubin Observatory, an 8.4-meter-wide telescope funded by the United States and built in Chile. Because it will photograph the entire visible sky every three days, it will be particularly vulnerable to the streaks left by satellites on its images. Astronomers are working on ways to mitigate the damage, such as algorithms that can identify and eliminate satellite fringes in the data, but fixing the data takes a lot of time and effort.

The increase in the number of satellites also has the potential to have a negative impact on the field of radio astronomy and increase the amount of space debris. Other broader effects could affect life worldwide: The presence of satellites causes background light to appear in the sky, which can disorient animals that rely on celestial navigation. In addition, satellite stripes interfere with human knowledge systems, such as indigenous knowledge systems that rely on information from dark skies to mark important events throughout the year.

Some satellite operators have been working to alleviate the problem. SpaceX has tested ways to reduce the brightness of starlink, which includes installing a sun visor. SpaceX engineer David Goldstein said earlier this month that SpaceX is working on other mitigations, such as adding stickers or other materials to satellite mirrors to reflect light away from Earth. How effective this approach will be is still being studied.

In recent days, the International Astronomical Union (IAU) will launch a website that includes tools to help telescope operators predict satellite positions so they can point their instruments elsewhere.

It is worth mentioning that while the IAU and other astronomical organizations have been urging the United Nations to acknowledge the problem, there is currently no law on how bright a satellite should be in the night sky. At the meeting of the United Nations Committee on the Peaceful Uses of Outer Space, to be held in Vienna on 1 June, representatives from many countries will discuss the protection of the sky. (Source: China Science Daily Xin Yu)

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