- #1
kiwikiwi79
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Why is it difficult to measure the perihelion advance of the planet Venus? Please help me answer this question in details...Thank you~ 
Why is it difficult to measure the perihelion advance of the planet Venus? Help
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Discussion Overview
The discussion revolves around the challenges of measuring the perihelion advance of Venus, exploring various factors that contribute to the difficulty in obtaining precise measurements. Participants address theoretical, observational, and geometrical aspects of the problem.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants note that Venus' orbit is nearly circular, which may make the perihelion location less distinct and complicate measurements.
- It is mentioned that Venus' orbital plane is inclined more than 3 degrees to the Earth's orbital plane, potentially affecting measurement accuracy.
- Participants highlight that the rate of perihelion advance for Venus is significantly smaller than that of Mercury, being about 8 seconds of arc per century, which raises concerns about measurement precision.
- One participant suggests that the curvature of spacetime near the Sun is a factor in the perihelion advance, while another clarifies that the dominant source of perihelion advance is perturbations from other planets.
- There is a discussion about the need to eliminate perturbations from other planets to accurately measure perihelion advance, with references to angular and linear measurements of advance.
- Some participants speculate whether Venus' retrograde motion could influence the measurement of its perihelion advance.
Areas of Agreement / Disagreement
Participants express various viewpoints regarding the factors affecting the measurement of Venus' perihelion advance, with no consensus reached on the primary challenges or the implications of different factors discussed.
Contextual Notes
Participants mention the need for precision in measurements and calculations, as well as the influence of orbital perturbations, but do not resolve the complexities involved in these aspects.
- #2
Andrew Mason
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Venus' orbit is practically circular so the perihelion location is less distinct. Venus' orbital plane in inclined more than 3 degress to the plane of the Earth's orbit. I don't know if that makes it more difficult to measure. The main reason is probably that the rate of advance is so small. Mercury's perihelion advance is about 10 minutes/century. Venus' is about 8 seconds of arc per century.kiwikiwi79 said:Why is it difficult to measure the perihelion advance of the planet Venus? Please help me answer this question in details...Thank you~
AM
- #3
pinkie
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The curvature of space time closer to the sun is also a factor, right?
- #4
SpaceTiger
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pinkie said:
If you're talking only about GR corrections, then yes, but the dominant source of perihelion advance in planetary orbits is perturbations from other planets.
- #5
Astronuc
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So, it would appear to be a matter of precision of either measurement or calculation, and a matter of the geometry of the orbit (almost circular). I imagine the perturbations in the orbit due to other planets are on the order of a few seconds of arc.Andrew Mason said:
- #6
Ian
- 88
- 1
KiwiKiwi,
The best way to measure the perhelion advance of any of the solar system planets is to first eliminate the peturbations of the other planets, then calculate the length of advance as opposed to the angular advance.
For Mercury the angular advance is about 43 seconds of arc, less for Venus and even more so for the earth; if we work with the length of advance instead (the length of the arc subtended by the angle of advance) it is the same for all planets and is approximately 27833.859 metres.
This length is determined only by the mass of the sun, G, and the velocity of light. Since this length is the same for all the planets in their orbits after the corrections for orbital ellipticity are removed we really ought to say that the perhelion advance is the same for all planets regardless of their distance from the sun.
The best way to measure the perhelion advance of any of the solar system planets is to first eliminate the peturbations of the other planets, then calculate the length of advance as opposed to the angular advance.
For Mercury the angular advance is about 43 seconds of arc, less for Venus and even more so for the earth; if we work with the length of advance instead (the length of the arc subtended by the angle of advance) it is the same for all planets and is approximately 27833.859 metres.
This length is determined only by the mass of the sun, G, and the velocity of light. Since this length is the same for all the planets in their orbits after the corrections for orbital ellipticity are removed we really ought to say that the perhelion advance is the same for all planets regardless of their distance from the sun.
- #7
Mariko
- 64
- 0
i don't know weather this helps but maybe it could have some thing to do with the fact Venus is in retrograde?
- #8
Mariko
- 64
- 0
i don't know weather this helps but maybe it could have some thing to do with the fact Venus is retrograde?
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