<p>Well, it depends on the assumptions that you're going to make:</p>
<ol>
<li>In the Keplerian case (Newton dynamics, two body problem): Yes, due to symmetry of the problem.</li>
<li>Taking precession due to General Relativity into account: No.</li>
<li>Full (simplified) N-body calculation taking perturbations into account, esp. Jupiter: Never</li>
</ol>
<p>In order to find the exact perihelion and aphelion dates, use JPL's WebGeoCalc as described in this <a href="https://astronomy.stackexchange.com/questions/11899/what-is-the-format-of-the-data-from-the-jpls-horizons-system#answer-11901">answer to another question on Astronomy Stack Exchange</a></p>

CC BY-SA 4.0
2024-12-17T08:05:24.820Z
For #2 what is the difference in the semi-periods?
ProfRob
CC BY-SA 4.0
2024-12-17T07:54:44.580Z
2024-12-17T07:54:44.580Z
Grimaldi
<p>Is the period of Mercury going from its aphelion to perihelion the same as when it goes from its perihelion to aphelion? Namely what is experimental data of the periods both inward going and outward going.</p>
<hr />
<p>This question arose in my study of deriving the period of an orbit of a planet taking into accounts GR effects (Schwarzchild model). I determined the period of a planet going from the perihelion to the aphelion and doubled it. But I thought is this correct?</p>
<p>So the question regarding experimental data.</p>
<p>In my model the period is derived from a derivative <span class="math-container">$dr/dt$</span> which is function of <span class="math-container">$P(r)$</span> [not stated here] which is solely dependent upon the radial length <span class="math-container">$r$</span>.</p>
<p>I am NOW thinking even though the path is different inward going and outward going, the radial length <span class="math-container">$r$</span> still goes from aphelion radius to the perihelion radius so at some place <span class="math-container">$r$</span> (but different <span class="math-container">$\theta$</span> ) it will have same  derivative <span class="math-container">$dr/dt$</span> and also shape <span class="math-container">$dr/d\theta$</span> due to the symmetry of the Schwarzchild metric. So doubling it seems okay.</p>
<p>If it is different how do you take this account in the modeling?
Many thanks for the references.</p>

CC BY-SA 4.0
2024-12-16T03:03:09.193Z
They'd be identical, if Mercury's orbit didn't precess.
PM 2Ring
CC BY-SA 4.0
2024-12-16T03:43:36.173Z
You can get good data from [Horizons](https://ssd.jpl.nasa.gov/horizons/); the JPL ephemeris data is fitted to numerous ground- and space-based observations. It's a little bit fiddly getting precise perihelion & aphelion times, though. https://i.sstatic.net/82OgZt5T.png
PM 2Ring
CC BY-SA 4.0
2024-12-17T08:22:07.673Z
From https://astronomy.stackexchange.com/q/49253/16685 the total precession of Mercury's orbit is 575.3 (arcsec/Julian century), with the precession due to GR effects being around 43 arcsec/cy.
PM 2Ring
<mercury>
What is the period of Mercury from aphelion to perihelion compared to perihelion to aphelion
pwm
# What is the period of Mercury from aphelion to perihelion compared to perihelion to aphelion

(Asked by: username_0 on 2024-12-16)

Is the period of Mercury going from its aphelion to perihelion the same as when it goes from its perihelion to aphelion? Namely what is experimental data of the periods both inward going and outward going.

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This question arose in my study of deriving the period of an orbit of a planet taking into accounts GR effects (Schwarzchild model). I determined the period of a planet going from the perihelion to the aphelion and doubled it. But I thought is this correct?

So the question regarding experimental data.

In my model the period is derived from a derivative $dr/dt$ which is function of $P(r)$ [not stated here] which is solely dependent upon the radial length $r$.

I am NOW thinking even though the path is different inward going and outward going, the radial length $r$ still goes from aphelion radius to the perihelion radius so at some place $r$ (but different $\theta$ ) it will have same derivative $dr/dt$ and also shape $dr/d\theta$ due to the symmetry of the Schwarzchild metric. So doubling it seems okay.

If it is different how do you take this account in the modeling?
Many thanks for the references.

**Tags:** mercury
> **Comments:**
> **username_1**: They'd be identical, if Mercury's orbit didn't precess.  
> **username_1**: You can get good data from [Horizons](https://ssd.jpl.nasa.gov/horizons/); the JPL ephemeris data is fitted to numerous ground- and space-based observations. It's a little bit fiddly getting precise perihelion & aphelion times, though. https://i.sstatic.net/82OgZt5T.png  
> **username_1**: From https://astronomy.stackexchange.com/q/49253/16685 the total precession of Mercury's orbit is 575.3 (arcsec/Julian century), with the precession due to GR effects being around 43 arcsec/cy.  

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## 1 answers

### Answer by username_2 on 2024-12-17. Score: 1

Well, it depends on the assumptions that you're going to make:

1. In the Keplerian case (Newton dynamics, two body problem): Yes, due to symmetry of the problem.
2. Taking precession due to General Relativity into account: No.
3. Full (simplified) N-body calculation taking perturbations into account, esp. Jupiter: Never

In order to find the exact perihelion and aphelion dates, use JPL's WebGeoCalc as described in this [answer to another question on Astronomy Stack Exchange](https://astronomy.stackexchange.com/questions/11899/what-is-the-format-of-the-data-from-the-jpls-horizons-system#answer-11901)

> **Comments:**
> **username_3**: For #2 what is the difference in the semi-periods?  

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