# Issue with Stellarium: transit of Venus (find the parallax)

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yucheng
TL;DR Summary
I am having problems using Stellarium. I was trying to find the parallax of the transit of Venus as viewed from two different locations. I am not sure whether the results given by Stellarium is accurate.

These are the two snapshot (on Stellarium) of the Third Contact between Venus and the Sun at the same time at different locations on Earth. The top image is viewd from Quito, Ecuador, the bottom image is from Harrisburg. I am supposed to determine the parallax. The angles were calculated using Geogebra. It appearrs that instead of revealing the parallax, Stellarium merely rotates the sun and the Venus.

1. Is this supposed to be the right view from the respective locations?
2. How should one calculate the parallax?

P.S. this exercise was proposed here Using a transit of Venus to determine the Astronomical Unit, using another planetarium application though.

P.S.S.

This was what I tried, where the white boxes refer to the length.

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## Answers and Replies

Staff Emeritus
2022 Award
This is a very specific problem and I'm not sure we have anyone here who can really answer it, as PF isn't a specialized astronomy forum. Best of luck to you though.

yucheng
This is a very specific problem and I'm not sure we have anyone here who can really answer it, as PF isn't a specialized astronomy forum. Best of luck to you though.
Hmm, thanks! Let me try to ask this somewhere else (I just realized there's a Stellarium mailing list), while I wait here.

Gold Member
Some quick estimates on the calculator seems to suggest that two simultaneous observers on a 12000 km baseline (just to take a near-maximum baseline distance) can expect a parallax of venus relative to the sun at around 0.7 arcmin or just around 2% of the diameter of the sun disc. If that is correct, you may have a hard time picking that number up from a "simulated" measurement setup.

yucheng
yucheng
Some quick estimates on the calculator seems to suggest that two simultaneous observers on a 12000 km baseline (just to take a near-maximum baseline distance) can expect a parallax of venus relative to the sun at around 0.7 arcmin or just around 2% of the diameter of the sun disc. If that is correct, you may have a hard time picking that number up from a "simulated" measurement setup.
Oops, looks like I should have tried estimating first.

Filip Larsen
Mentor
I'm not sure, but I think observation from different latitudes causes the sun to be viewed at different rotation angles.

Gold Member
I'm not sure, but I think observation from different latitudes causes the sun to be viewed at different rotation angles.
I concur. I have only tried the web version (which it otherwise quite nicely done) and it appears to always render the sky using the local horizon coordinate system ("azimuthal grid"). Not sure if the desktop versions have options to render in, say, equatorial or heliocentric coordinates, but if it does that should then "remove" the relative rotation between snapshots from two different observers.

yucheng
I concur. I have only tried the web version (which it otherwise quite nicely done) and it appears to always render the sky using the local horizon coordinate system ("azimuthal grid"). Not sure if the desktop versions have options to render in, say, equatorial or heliocentric coordinates, but if it does that should then "remove" the relative rotation between snapshots from two different observers.
I tried asking here: