Starlink satellites pose a threat to astrophotography


Elon Musk has a big goal: he wants to provide billions of people around the world with fast internet. His company SpaceX has already launched 60 satellites in space until about 2017, it should be almost 12,000. The Starlink project promises good business and can actually close any radio hole on Earth – but astronomers and astrophotographers are worried: will more satellites than stars be seen in the sky in the future? Can you still take pictures of the starry sky without disturbing features?

After the starlink exposed the first 60 satellites in Earth orbit last Friday, there were soon clear sightings. Videos show how they traverse the sky like a pearl necklace:

"When I saw satellites for the first time, my jaw dropped like hell," says Carolin Liefke, an astrophysicist at the Astronomy House in Heidelberg. There were several questions from people who were wondering about the strange phenomenon. But the pearl effect only happened when the satellites were sequentially abandoned and put into orbit.

In the photos, satellites weighing up to five pounds are often seen as line marks, because astrophotographers often work with long periods of exposure. This is happening from time to time because about 5,000 other satellites are already in orbit. Some photographers, especially beginners, are even happy when they capture these celestial objects.

But ambitious amateur photographers and even more professional astronomers do not want satellites in their recordings. However, it is not yet clear how great the satellites' influence will be. Elon Musk minimized the problem: there are already 4900 satellites in orbit that people would not notice.

It's about helping billions of disadvantaged people, that's the key. At the same time, he would guarantee that Starlink had no negative impact on astronomy, he assured: Science is very important to him.

Will the sky soon be filled with bright satellites? Experts do not consider this very likely. Already the experience of the last few days shows: Starlink satellites were particularly bright to see when they were exposed – and only in some places. Meanwhile, they have spread and are much weaker. The satellites do not shine anyway, they have no lights, but only reflect sunlight, which they drive at a certain angle to Earth. "How brilliant the satellites will be seen in the end, you still can not estimate," Liefke said.

Especially since the 12,000 satellites are to be positioned at three different heights: 340, 550 and 1200 kilometers. At high altitudes they are more and more illuminated by the light of the sun – but they shine weaker, because they are more distant. On the other hand, the closest satellites could be better viewed – but only in the hours after sunrise and before sunrise. Musk also points this out on Twitter: "The satellites will be dark when the stars are visible."

However, Liefke explains that this is not always helpful to astronomers: in summer, there are only very short or not too dark nights in the northern latitudes – so satellites could worry almost all night long. However, not all 12,000 satellites will always be in the sky at the same time: "It is estimated that there will be a maximum of 500 per night." Lay people will probably not notice objects, says the expert, especially if they are in or near living Cities where the sky is never really dark.

Some amateur astrophotographers, however, already dread the end of their hobbies, which is often not easy to practice due to increasing light pollution. In fact, many satellite tracks can be seen in pictures taken with wide angles and long exposure. However, today a bigger problem is the much more visible aircraft and its Kondenzstreifen. These unwanted effects can be removed in individual images, but with image editing programs such as Gimp, Lightroom or Photoshop, but relatively easy – it takes only a little time.

Many disturbances can be eliminated with software

Even in the so-called deep sky photographs, in which, for example, galaxies are photographed, these traits can be eliminated with special techniques. Therefore, there is software that processes the so-called stacks (stacking) with many (often hundreds) images of an object to calculate disturbing factors. But here too, if there are too many photos with satellite tracks, the final image quality will be reduced.

How do professional astronomers react? "The anger is even greater than the amateurs," says astrophysicist Liefke. Often, they would track the sky with large image fields, for example, to discover asteroids, which are betrayed by positional shifts in the photos. These observations and professional measurements can be disturbed by many satellites. So far there are no official protests, says Liefke, but Starlink is a big topic in professional networks.

Musk wants to respond to protest

Liefke talks about raising awareness of the problem. In Elon Musk, the message from the Astro church apparently arrived. After he was initially legal on Twitter against critical issues and allegations, he finally relented a bit. When asked if he could not consider ways to reduce the reflectivity of satellites, such as through a different paint or special mirrors, he replied on Twitter: "I agree, I saw a note to the Starlink team last week sent albedo reduction. "Albedo is the retroreflective power of surfaces.

And he points out that you can only tell how great the effect is when the satellites reach their target positions. This also means Liefke: "We have to wait until the satellites reach their orbit and unfold their solar panels."

However, solutions must be found before all satellites are in space. Especially because Musk is not the only one who wants to do business in space. The company OneWeb, of the American Greg Wyler, wants to meet with Airbus hundreds of minisatellites in orbit. Apparently, Amazon boss Jeff Bezos is also planning a project to give people access to the Internet around the world with the help of thousands of satellites.

Anyone who wants to know their location when Starlink satellites can be seen can get information on the Internet, including, or Satmap.

Read too:
The starry sky in June

From Udo Harms / RND


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