# What can Jupiter's spectrograph tell us other than its rotational velocity?

I have data of a Jupiter's image and the spectra of each pixel in the image, and I am playing around to see what I can do with it.

I have managed to find Jupiter's rotational velocity by finding the difference between the wavelengths of H-$$\alpha$$ line of two pixels one at the centre and another at the edge of Jupiter's data cube.

I have also managed to identify a few spectral emission lines of Jupiter's red spot.

Is it possible to do something similar and find the orbital velocity, or the distance between Earth and Jupiter? Or is there anything else that a spectrum of Jupiter can tell us?

• Whatever you extract has to be an intrinsic property of Jupiter, so forget anything "relative" such as orbital velocity. Of course the collected light can be put in relation to distance to the source, but for this one must know or postulate the brightness of the source. It is not the case, at least without mixing various previous knowledge. In general, absolute intensity is not a real spectroscopical feature. – Alchimista Oct 5 '20 at 6:03
• There might be some sort of dispersive effect that can tell you something about the Earth's atmosphere, or vice versa. In fact, unless I'm mistaken, theoretically you could infer the distance based on the dispersion, but I'm not sure how accurately based on the resolution of your data! – Dagelf Oct 5 '20 at 7:42
• @Dagelf If there was some hypothetical "dispersive effect" from the Earth's atmosphere (leaving aside what that's supposed to mean), the most you could learn would be "Jupiter is somewhere beyond the Earth's atmsophere". – Peter Erwin Oct 6 '20 at 9:57
• Depending on the absolute accuracy of your wavelength calibration, you could measure the radial velocity of Jupiter relative to the Earth from the Doppler shift of Jupiter's emission line, but that's only part of the full orbital velocity vector. – Peter Erwin Oct 6 '20 at 10:00
• @PeterErwin Why do you say "hypothetical"? Doesn't light always disperse when it enters a medium with a different density, because the different wavelengths are slowed down at different rates? Are you saying that it has only to do with the angle, and nothing to do with the distance? – Dagelf Oct 21 '20 at 4:46