I just can’t compute how this is possible. How can a telescope detect a gas, which isn’t even visible to the naked eye, on a planet that is an incomprehensible distance away.
[Source](https://www.bbc.co.uk/news/science-environment-66786611)
In: 143
The telescopes don’t see the gas any more than your eyes see our own atmosphere, but that doesn’t mean things are unknowable. We see trees and flags wave in the wind, and clouds form and move, we have rainbows and light pollution, stars twinkle — all consequences of gasses we can’t see (but we do see the results). The question of understanding distant planets works in the same way, we can understand the gasses and atmosphere even without seeing them directly IF we can get an idea of what the gasses are doing via other methods.
In the instance of this telescope & planet, the telescopes take a picture of the star and then another and another (and so on) looking for little eclipses from when the planet crosses in front of the star from our point of view.
And when THAT happens we can get a picture that includes the planet. And if we’re lucky, we can catch a hint of the rainbow created by the planet’s atmosphere (if it has an atmosphere). This works much the same way as a rainbow here on Earth.
And if we have a rainbow (a spectrum) THAT can be analyzed to see what is causing it, as not all rainbows are created equal. On their face, all rainbows look similar, but that is partly because the light rays are going every which way. If you have a polarizer (like polarized sunglasses) you can filter out the “every which way” effect and you get a rainbow with a long series of dark & bright spots, I’ve linked the periodic table of elements so you can see what each different element’s ‘fingerprint’ looks like in this situation; and of course each molecule has a different fingerprint as well.
[Periodic Table of Elements](http://2.bp.blogspot.com/-rh08lgewe08/UdpI0-NbEAI/AAAAAAAAAFI/2_SRy2xEEZA/s400/spctelem.png)
[What our sun looks like](https://image.slidesharecdn.com/spectroscopy-090508075019-phpapp01/75/spectroscopy-12-2048.jpg?cb=1669870731) (other stars, and planets) will have their own unique combinations.
By examining the fingerprints in the “rainbow” scientists can determine what gasses are causing that particular appearance even without seeing the gasses directly.
If you want to know how each element results in a different fingerprint, that’s a little more involved, but a simple (and very incorrect) analogy is to imagine that each set of electrons creates a kind of “shadow” that affects a very narrow slice of the spectrum, and because each element and each molecule have a unique combination of electron configurations…you can get a unique “shadow” pattern in the rainbow. They are *not* shadows, but explaining the physics behind is more high school science than ELI5 and should be its own question.
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