Yes, SpaceX's Starlink Satellites Are Photobombing Modern Astronomy

'The number of affected images is clearly increasing with time'
Grant Currin
A series of Starlink satellites pass by as a meteor burns through the atmosphere. NASA  /  Egon Filter

Too much of a good thing is almost always bad.

But is this true for Starlink?

For years, astronomers have warned that SpaceX's goal of lifting more than 10,000 Starlink satellites into low-Earth orbit would clutter the night sky. But now we're finally getting the scientific word on the increasingly crowded skies.

In 22 months, researchers from Caltech’s Palomar Observatory analyzed and cataloged more than 5,000 bright streaks attributable to Starlink satellites, according to a recent study published in The Astrophysical Journal Letters. And most concerning was the change witnessed in images taken at twilight.

When the study began, less than one in 200 images taken at that time of day contained a satellite. By September 2021, the number was almost one in five.

But do orbital satellites really pose a threat to astronomy? Some fields "may be more significantly affected by the increasing number of satellite streaks," said the study's lead author, Professor Przemek Mróz of the University of Warsaw, in an email interview with Interesting Engineering.

This interview has been edited for length and clarity.

Interesting Engineering: What sort of science is typically done at the Zwicky Transient Facility, where this research was conducted? How did that data inform this study?

Przemek Mróz: Zwicky Transient Facility (ZTF) is one of the largest sky surveys. It observes the whole visible sky every two nights to search for objects that change their brightness or move. ZTF also captures images of satellite steaks when the satellites cross the field of view of the telescope. We analyzed archival images taken with the ZTF telescope between November 2019 and September 2021 to search for satellite streaks that were captured in our data.

IE: Many astronomers are worried that the Starlink satellite network will pollute the night sky and make astronomy harder to do. Do your results support those concerns?

PM: The problem of satellites in our sky is a concern. Our study was meant to provide data to help assess the impact of satellite streaks on astronomical observations, other instruments at other observatories can use these data to assess whether (and how) their observations might be affected.

We found that satellite streaks do not significantly affect our science because less than one-tenth of one percent of the image pixels are affected by one satellite streak. In ZTF, there is a small chance that we would miss an asteroid or another event hidden behind a satellite streak. Because we take images of the whole sky every two days, we would likely catch a missing asteroid later in other images.

However, astronomers carry out different types of observations (spectroscopy, deep imaging), and each type of observation should be individually assessed to determine whether the science is significantly affected.

IE: A lot of Starlink supporters claim that ground-based telescopes are limited by so many other variables that Starlink isn’t really a big problem. What do you think about that position?

PM: Our study shows that the ZTF images taken at twilight are being increasingly affected by satellite streaks, but this is not affecting our science operations overall. However, other types of astronomical observations may be more significantly affected by the increasing number of satellite streaks.

IE: Will these satellites affect naked-eye stargazing?

PM: Our study indicates that the mean brightness of Starlink satellites on operational orbits is about 6.8 mag and is below the naked-eye limit (about 6 mag). However, the satellites may be brighter during orbit rise or deorbiting.

Astronomers are 'just beginning' to grasp the impact of internet satellites

While science at the ZTF probably won't be affected by satellites, Mróz pointed to a recent report, funded in part by the National Science Foundation, that paints a different picture for other types of astronomy.  The authors found that “[e]xisting and planned large constellations of bright satellites in low-Earth orbit… will fundamentally change astronomical observing at optical and near-infrared… wavelengths.” Starlink CEO Elon Musk has denied such claims.

Clearly, satellites in low-Earth orbit are already starring in plenty of images taken by ground-based telescopes, but it's too early to say how the huge constellations planned by firms, including Starlink, Kuiper, and Telesat, will ultimately affect the night sky. As the authors of the NSF report write,  “[a]stronomers are just beginning to understand the full range of impacts on the discipline."

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