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Comment by vanderZwan | Hacker News Reader

When surrounded by pitch dark the human eye is capable of spotting the light of a candle from tens, possibly hundreds miles away at a clear night, and yet under those conditions it would also be perfectly possible to hide an elephant a few meters away from someone

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Why can’t we look for moving dim spots in the cosmic microwave background?

The CMB consists of longer wavelengths than light (around 1 mm compared to 500 nm, or 2000 times larger), so a radio telescope capable of resolving an angle as small as a small planet 100 AU away would be enormous, kilometers in diameter.

It's also a lot easier to point a telescope at the extremely specific points. Even if the CMB could be used as effectively as stars, you can't aim a directional telescope at the entire sky all at once. You have to pick a spot to stare at & get lucky.

Try looking out the back of your head for the planet hiding right behind you. Once you figure out that you have to turn around, the planet might not be there anymore :) We could build telescopes & point them in every direction though!

The issue seems to be one of illumination... as unlikely as it is, would it help to off a big bright bomb or two as "flashlights" to speed up the search?

It's already illuminated by the huge fusion bomb at the centre of the Solar System. We can't make bigger or brighter bombs than that.

Sure you can. Its inverse-square law which extinguishes the brightest flame (except of course a nova or supernova). A much nearer explosion would be much, much brighter. But you have to have some idea where to set it off.

So if we knew the answer to our question (where to set it off) it would be easy to get the answer to the question (where that object is).

Well, yes. True. Not spectacularly informative though.

I call bullshit. The horizon is only about 3 miles away.

Elevation significantly increases visibility, such that the longest photographed distance on Earth is 443km :)

You make a valid point (although another counter-argument has already been given.

But speaking purely in terms of human eye sensitivity this has been confirmed in an indirect way at least: the faintest star visible to the human eye (under perfect conditions) is comparable in light intensity.

EDIT: also, sky lanterns https://en.wikipedia.org/wiki/Sky_lantern

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