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

• I
• yucheng
In summary, the two Stellarium snapshots of the Third Contact between Venus and the Sun at the same time at different locations on Earth show that the program simply rotates the sun and Venus instead of revealing the parallax.
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.

Last edited:
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.

Drakkith said:
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.

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

russ_watters said:
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.

Filip Larsen said:
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.

Indeed, I should have used equatorial mount to disable rotation. Tried it in stellarium just now, and it works.

collinsmark and Drakkith

## 1. What is the transit of Venus?

The transit of Venus is a rare astronomical event in which the planet Venus passes directly between the Earth and the Sun. This event can only occur when Venus is in its inferior conjunction, meaning it is at its closest point to Earth in its orbit.

## 2. Why is the transit of Venus important?

The transit of Venus is important because it allows scientists to measure the parallax of Venus. This is the apparent shift in the position of an object when viewed from different locations. By observing the transit of Venus from different locations on Earth, scientists can calculate the distance between Earth and the Sun, known as the astronomical unit (AU).

## 3. What is the parallax?

The parallax is the apparent shift in the position of an object when viewed from different locations. In the case of the transit of Venus, the parallax is the difference in the position of Venus as seen from different points on Earth during the event.

## 4. How can Stellarium help with observing the transit of Venus?

Stellarium is a free and open-source planetarium software that can accurately simulate the positions of celestial objects in the sky. By setting the date and time of the transit of Venus, users can see the exact path of Venus as it crosses the Sun, making it easier to plan for observation.

## 5. What causes issues with the transit of Venus in Stellarium?

One of the main issues with the transit of Venus in Stellarium is the accuracy of the parallax measurement. This is due to the fact that Stellarium uses a simplified model of the solar system, which may not account for all the factors that affect the parallax. Additionally, the user's location and time settings must be precise in order to accurately simulate the transit.

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