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SpaceX's Starlink constellation could place up to 42000 satellites around the Earth. Would aliens with their own telescopes notice them? They would be about 150 km apart and could reflect light of this wavelength produced by the Sun's corona. Waves bouncing off the ionosphere could perhaps form a detectable diffraction pattern.

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    $\begingroup$ The Earth itself would be way easier (but still very difficult) to detect. $\endgroup$ Nov 9, 2023 at 16:51
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    $\begingroup$ It's not clear what you mean by "distant planet" Do you mean like "Mars" or do you mean a planet around a different star. $\endgroup$
    – James K
    Nov 9, 2023 at 18:17
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    $\begingroup$ It would take millions of satellites to cover the Earth with 10km gaps. I don't really get the connection to ultralong wavelength radio waves, or why you think a space network of satellites would reflect ultralong wavelength radiowaves. $\endgroup$
    – James K
    Nov 9, 2023 at 19:03
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    $\begingroup$ Utterly undetectable. Even assuming millions of satellites, from a nearby solar system the separation of the Earth and the sun would be less than an arcsecond. One would need a colossal interferometer to even separate the Earth from the sun. And then the sun would be so much brighter than the reflection from the Earth. Of course you can say "alien technology" and who knows what those colourful characters can build... but no. Starlink satellites would not be easily detected from an exoplanet $\endgroup$
    – James K
    Nov 9, 2023 at 21:32
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    $\begingroup$ If I hold a dime in front of your eye, you won't be able to see anything but the dime. The dime is still invisibly small from a mile away, though. $\endgroup$ Nov 9, 2023 at 22:11

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Not in any way that is special to the Starlink satellites. Many satellites can interfere with earth-based astronomy because they are very close to the earth. A reflection off a satellite that is a few hundred miles away can be brighter than a star that is a few tens of trillions of miles away. But, from a different star, both our sun and the satellites are a few tens of trillions of miles away, and the satellites' reflected light is negligible.

Of course, it is possible to imagine faraway supertelescopes that could detect human artifacts. But such a telescope could also detect the ISS and Iridium flares, among many other things. The Starlink satellites' nuisance effect for earthly astronomers doesn't really make them easier to detect from Alpha Centauri.

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