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 Betreff des Beitrags: Venus-Jupiter Conjunction
BeitragVerfasst: 31. August 2016, 15:44:28 PM 
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Dauernutzer

Registriert: 23. Februar 2008, 19:33:52 PM
Beiträge: 100
Hello,

On August, 27, Jupiter (Zeus) almost had an affair with Venus! Juno (Zeus' wife) -- disguised as a spacecraft sent by NASA -- took a picture of her husband on that date (seen here: http://www.jpl.nasa.gov/news/news.php?feature=6606), but Venus was not visible in that picture! :wink:
I believe this clearly demonstrates how Zeus misbehaved in the Ancient Greek Mythology, and how Zeus could meet beautiful earthly women without Juno noticing it! ::)
Well, I also collected NASA/JPL ephemeris data that hints at Venus running away from Jupiter! 8-) So I decided to observe this, to prove that Venus was in fact running towards the Earth faster (-7.55 km/s) than Jupiter (+10.14 km/s). I wanted to fit Jupiter and Venus on the same slit of my spectrograph and measure radial velocity! They got really close to each other from my longitude before setting (8 arc-minutes, at time of observation).

My goal: observe a differential radial velocity between Venus and Jupiter of +17.7 km/s! (the real challenge here is in characterizing the distortion of the spectrum in my Lhires)

Due to unforeseen problems, I could not use the right telescope (focal distance) necessary, so I had to observe both planets separately!
I quickly discovered the effect of a dimmer Jupiter compared to Venus, and the atmosphere was unstable (5 degrees above horizon!!).
Since I now had to observe both planets separately, I decided to orient the slit with East-West, to measure Jupiter's equatorial rotation!
Dateianhang:
Dateikommentar: Spectrum around H-alpha, LhiresIII 2400 Atik-414
jv_v0.jpg
jv_v0.jpg [ 69.08 KiB | 793 mal betrachtet ]
From the separate spectra of both planets, I could not visibly detect any shift in the lines reflecting on Venus.
From Jupiter, however, it seems to be spinning at 9 km/s (mabye I did not have the slit precisely at the equator). But because I can estimate that Jupiter is in fact moving away (redshift) at very close to 10 km/s!
However, I was expecting to see Venus move towards the observer at 7.69 km/s, and I could not detect any visible shift in the lines!

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 Betreff des Beitrags: Re: Venus-Jupiter Conjunction
BeitragVerfasst: 03. September 2016, 09:46:47 AM 
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Dauernutzer
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Registriert: 15. September 2014, 14:05:45 PM
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Filipe,

impressive work - congratulations.

It is interesting that the expccted Venus rotation and relative velocity cannot be detected easily. I would say, that the difficulty can be so separate these two effect, and that the rotation of the planet is also individual.

Regarding Venus, I know that her atmosphere is build up in layers, and may be there is a differential rotation, so it is crucial where you put the slit of the spectrograph.

Furthermore, in the Venus' atmosphere CO is more abundant in clouds in the upper atmosphere. So it would be helpful to look for the CO-signature to identify the rotation.
The CO is produced by the intense UV sunlight that dissociates CO2 molecules. By the way this is a clear difference between Venus and Jupiter, so maybe this help your in analysing the differences.

Best wishes,
Michael

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 Betreff des Beitrags: Re: Venus-Jupiter Conjunction
BeitragVerfasst: 13. September 2016, 17:28:27 PM 
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Dauernutzer

Registriert: 23. Februar 2008, 19:33:52 PM
Beiträge: 100
Thank you,
Venus is a mystery to me.. I always heard that there are strong winds, but I also thought they would be hard to see with my spectral resolution and dispersion... The rotation it self of the surface is to forget detection, as it is almost stopped. In sum, I was expecting Venus would behave very much like a "static-rotation" sphere, reflecting sunlight, orbiting the Sun.
Zitat:
So it would be helpful to look for the CO-signature to identify the rotation.
Interesting! I have a prejudice/bias against molecules in atmospheres, particularly if some pressure is present... I always assume they produce broad features, or are too far in the IR (or radio) for me to look for... But maybe that is something I could try to investigate... Thank you!

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