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For earth yes, because we know that human civilizations generate tons of light pollution. Perhaps an alien civilization would be less careless, which means a dark night-side wouldn't prove anything. Which means that looking at night is not as effective as looking at day.

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That light pollution has only existed for a tiny tiny fraction of the time since life first evolved on Earth. It's entirely conceivable that in another 1000 years (a blink of the astronomical eye) it will no longer occur - so trying to detect whether life exists on any random planet/moon that way seems a low probability exercise, but granted if it's cheap to do you might as well (conceivably there might be other detection methods based on electromagnetic radiation etc. that would reveal more information on the dark side of a planetary body too).

I'm really confused about how this responds to what I wrote.

Sorry, was meant as a reply to the post you were replying to!

I wouldn't assume it's carelessness for the alien civilization.

The night-side view is merely looking for surface-generated radiation with less interference from external radiation.

Most of our light pollution is caused by "carelessness". We put on way more lights than we reasonably need, and we put on the wrong kinds that are more confusing to wildlife.

Aliens might not do that. Their cities might be fairly dark at night.

Aliens might not even use light or radio based vision. They could be like bats and use echo location.

You are also assuming "intelligent life", and that it is sufficiently advanced to have created cities and some form of light bulb. (this could include a lantern). Without that you have to rely on other signs of life.

Electromagnetic radiation is pretty universal (ha). We might expect that many advanced life forms have ways to detect it.

Sure, but we also expect vastly more non advanced life

I'm not sure you've been following the conversation... I'm not wondering how we can find life, I said looking for city lights at night is a bad way to look for life.

So radio wave emissions are valid proof of life, but not emissions of visible light? Seems a bit arbitrary.

That's the opposite of what I'm saying. Checking the night side of a planet for visible light isn't useful because a technological civilization won't necessarily create large amounts of light pollution the way we do. If we happen to see nighttime light pollution that would be useful, but planning a mission around looking for it specifically would not make sense.

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