Study and Video of star passing behind a planet.

Pinball1970 said:
Below is a nice article with the video of the star passing behind the planet.

https://phys.org/news/2025-04-planetary-alignment-nasa-rare-opportunity.html

A large collaboration - the below gives detail on the teams involved and position of the telescopes used,

https://science.larc.nasa.gov/URANUS2025/
Click to expand...
Video seems to be just an animation rather than the real thing - and rather a blinding glimpse of the bleedin' obvious.

Slightly disappointingly, there is no discussion of how starlight passing through the atmosphere can reveal information on the composition, temperature, pressure and density of the atmosphere. It would also have been interesting to know something about this apparently unexpected high temperature in the outer atmosphere, which seems to be information they already have from earlier measurements (how?).

If this is done by IR, how do they get information on an atmosphere primarily composed of non-polar molecules like H₂ and He, which are transparent to IR radiation? Do they perhaps rely on the minor atmospheric components? H₂O? NH₃, CO₂......? And then make inferences from those about the atmosphere in general? Or is there some fancy scattering process they can use, e.g. from ice or other"dust" particles in the atmosphere, or something?

I suppose we'll have to wait for the findings to be published to find out.
 
exchemist said:
Slightly disappointingly, there is no discussion of how starlight passing through the atmosphere can reveal information on the composition, temperature, pressure and density of the atmosphere
Click to expand...

I am guessing a bit but the light source is behind passing through the atmosphere so useful spectral data?
 
Pinball1970 said:
Below is a nice article with the video of the star passing behind the planet.

https://phys.org/news/2025-04-planetary-alignment-nasa-rare-opportunity.html

A large collaboration - the below gives detail on the teams involved and position of the telescopes used,

https://science.larc.nasa.gov/URANUS2025/
Click to expand...

When it comes to celestial bodies that are tiny from our perspective -- involving either full blown "eclipses" or lesser astronomical transits -- I had heard of transit spectroscopy with respect to exoplanets, and planetary transits and occultations with each other in our solar system. But for some reason the latter occurring with distant stars never got highlighted for me, and the "scientific bonanza" associated with it.
_
 
exchemist said:
Well yes but as I said in my previous post, does that work? What absorptions do they look for?
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The gases will have their own signatures, Webb is doing similar with exoplanet spectroscopy.
Water, CO2 and methane infra red and Emission lines for Hydrogen.
Difference here the materials being measured here are much closer with the light source much further away, 400 light years.

Exactly how the extract pressure, temperature from all that is a guess.
Strength of the signal? Concentration? Especially since they have the data from no atmosphere to thin then thicker till everything is absorbed.
 
Pinball1970 said:
"light curve" is mentioned in one search. No idea how that works, different density more refraction? Greater density greater pressure?
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You're not meaning "curve of light" - as in deflection - are you?

Surely "light curve" literally means this curve:

1745505787278.png
 
Pinball1970 said:
The light is moving from a vacuum to a gas, so it would refract would it not?
That plus intensity falling off.
Click to expand...
Yes, of course. I was just wondering if you were perhaps reading too much into "light curve" as a part of the observations, as opposed to just the diagrammed curve.
 
DaveC426913 said:
Yes, of course. I was just wondering if you were perhaps reading too much into "light curve" as a part of the observations, as opposed to just the diagrammed curve.
Click to expand...
They used 18 different telescopes so intensity will only be one parameter I would have thought.
 
It's interesting this jump in the curve on occultation and reappearance:
1745510885302.png
I suspect this is due to refraction as it passes into and out of the limb of the planet's atmosphere.

I'm guessing the leading edge of the star's disc gets refracted from behind the planet, increasing its brightness momentarily.
 
Pinball1970 said:
"light curve" is mentioned in one search. No idea how that works, different density more refraction? Greater density greater pressure?
Click to expand...
I suppose density would affect refractive index, yes. Maybe the degree of Doppler broadening in an H absorption band would give an indication of temperature? But then there will also be pressure broadening as well from the uncertainty principle…. It must be difficult to disentangle effects of composition, pressure and temperature, I’d have thought. Let’s hope the eventual paper with the results gets some press coverage. Then all should become clear.
 
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