Astronomers are shedding the evening sky (and the radio sky) to satellite tv for pc mega-constellations

When was the last time you looked up into the night sky and saw the Milky Way? If you happen to live in a really remote area of ​​the world, your answer might be “last night.” If you live in one of the more “rural” areas of your country, you may remember that you used to see the Milky Way on a regular basis, but with the rise of LEDs, particularly the blue and white ones, the Milky Way is gradually out of your sight Country disappeared nights. For the vast majority of people in our little world, the answer is “never.”

Light pollution has gradually stolen the night from us. Powerful observatories like the Griffith Observatory were once blinded by our nighttime illuminations, and modern telescopes must be built in the most remote areas of the world where light pollution is still manageable. Although we don't notice it in the same way, the same is true for radio telescopes too. Our days are full of radio lights, from cell phones and Wi-Fi to the tire pressure sensors of a modern phone call. They all shine on the radio as brightly as an LED flashlight in the visible. But in recent years, both optical and radio telescopes have detected increasing light pollution from another source: constellation satellites.

Companies like Starlink have launched so many satellites that even in the most remote areas of the world, they can be regularly seen near the horizon, especially at dusk and dawn. With optical telescopes, the trails they produce can be mitigated to some extent by making them less reflective. However, for radio telescopes they pose a more serious and complex challenge.

Because Starlink and other constellations are communications satellites, they actively beam radio signals to Earth. Imagine if satellites constantly illuminated your house with powerful floodlights and you had the problem of radio observatories. One way to limit radio light pollution is to establish forbidden zones where satellites do not work. For example, Starlink satellites fall silent over key regions of the National Radio Quiet Zone as well as other major observatories around the world. This reduces light pollution but does not eliminate it.

An image of the galaxy group NGC 5353/4 taken with a telescope at the Lowell Observatory in Arizona, USA, on the night of Saturday, May 25, 2019. The diagonal lines running across the image are satellite tracks of reflected light larger than 25 Starlink satellites passed through the field of view of the telescope. Photo credit: Victoria Girgis/Lowell Observatory

As a recent study shows, radio signals from Starlink satellites are not narrowly focused. Even when they are silent over an observatory, they are active in areas close to the observatory, and stray radio light can contaminate observations. As satellite constellations become more common, this stray radio light will wash out the radio sky, much like LED lights from neighboring cities obscure your view of the Milky Way.

The situation has become so serious that the IAU Center for the Protection of the Dark, Quiet Sky from Satellite Constellation Interference (CPS) has called for concrete steps to save the night sky. They call on the international community to implement regulations to ensure that ground-based astronomy remains viable in the future.

It is clear that satellite constellations like Starlink are beneficial to many people around the world. For some regions, this is the only way to connect to the Internet. Likewise, inexpensive night lighting has allowed us to live a safer and more comfortable life. But it's worth being aware of what we stand to lose. Our view of heaven is deeply rooted in human culture and is worth preserving. We can all strive to better align our history with our future.

Reference: Dark, IAU, et al. “Call to protect dark and quiet skies from harmful interference from satellite constellations.” arXiv preprint arXiv:2412.08244 (2024).

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