<p>If you already have a geocentric <a href="https://en.wikipedia.org/wiki/Ecliptic_coordinate_system" rel="nofollow noreferrer">ecliptic longitude</a>, most likely no further correction is required.
When the ephemeris calculator computes each planet's heliocentric position (including Earth), it accounts for eccentricity by converting <a href="https://en.wikipedia.org/wiki/Mean_anomaly" rel="nofollow noreferrer">mean anomaly</a> to <a href="https://en.wikipedia.org/wiki/True_anomaly" rel="nofollow noreferrer">true anomaly</a>.</p>

CC BY-SA 4.0
2020-06-11T19:37:46.667Z
2020-06-11T19:37:46.667Z
Mike G
<p>What is the formula to plot an eccentric orbit on a perfect circle? I have estimated the full degrees each planet would occupy on a 360 degree wheel (natal chart) but how do I take into account a planet's ellipses not being perfectly circular? </p>

CC BY-SA 4.0
2020-06-11T10:13:43.647Z
Not sure I understand your question. If you want to be accurate, you will have to use ellipses, or varying movement velocity of the planet; its angular movement is slower when far from the Sun. However... 'natal charts' are astrology... and for all purposes  concerning that, the assumption of circles is just fine as deviations from circular orbits are very small.
planetmaker
CC BY-SA 4.0
2020-06-11T10:21:28.237Z
@planetmaker Ok thanks for that. I was wondering if astrology software even takes eccentricity into consideration. I know Mercury and Pluto have a higher eccentricity and want to be as accurate as possible.
skiventist
CC BY-SA 4.0
2020-06-11T10:27:31.863Z
Well... if you want to be more precise, you need to do the same math any sky chart programme does: take the ephemeris of the planets and integrate them over time (or interpolate between pre-supplied coordinates). the question is "how accurate is accurate enough"? What precision do you need for what value(s)? How accurate in time and place do you need to be?
planetmaker
CC BY-SA 4.0
2020-06-11T18:19:54.853Z
I’m voting to close this question because it doesn't appear to be concerned with astronomy except tangentially.
James K
CC BY-SA 4.0
2020-06-11T20:36:46.687Z
Was going to post in astrology but fathomed the astronomy bros would understand better. Thanks my dudes
skiventist
CC BY-SA 4.0
2020-06-12T23:05:49.360Z
An astrologer's ephemeris is typically based on precise JPL data (i.e. taking into account eccentricity, perturbations etc), with the right ascension expressed in 30-degree segments of the circle (i.e. the astrological "signs"). If the software incorporates that JPL data, or any equivalent precise data, then this will resolve the eccentricity issue. There's no simple formula that will calculate a planet's apparent position (as seen from Earth) based on the planet's elliptical orbit *and* Earth's elliptical orbit *and* the orbital perturbations caused by Jupiter and/or nearby planets.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2020-06-12T23:17:23.450Z
@JamesK You're absolutely correct that astrology questions don't belong here. However, this question is really about how to calculate a planet's right ascension, since that involves plotting the planet's position along the celestial equator which, by definition, is a circle. That seems perfectly on-topic to me. We shouldn't close a question merely because the science in the answer might be used for non-scientific purposes. I'm voting to leave the question open, although it could certainly do with some tighter wording.
Chappo Hasn't Forgotten
<observational-astronomy><positional-astronomy>
Map planetary eccentricity on a perfect circle?
skiventist
# Map planetary eccentricity on a perfect circle?

(Asked by: username_0 on 2020-06-11)

What is the formula to plot an eccentric orbit on a perfect circle? I have estimated the full degrees each planet would occupy on a 360 degree wheel (natal chart) but how do I take into account a planet's ellipses not being perfectly circular?

**Tags:** observational-astronomy, positional-astronomy

> **Comments:**
> **username_1**: Not sure I understand your question. If you want to be accurate, you will have to use ellipses, or varying movement velocity of the planet; its angular movement is slower when far from the Sun. However... 'natal charts' are astrology... and for all purposes  concerning that, the assumption of circles is just fine as deviations from circular orbits are very small.  
> **username_0**: @username_1 Ok thanks for that. I was wondering if astrology software even takes eccentricity into consideration. I know Mercury and Pluto have a higher eccentricity and want to be as accurate as possible.  
> **username_1**: Well... if you want to be more precise, you need to do the same math any sky chart programme does: take the ephemeris of the planets and integrate them over time (or interpolate between pre-supplied coordinates). the question is "how accurate is accurate enough"? What precision do you need for what value(s)? How accurate in time and place do you need to be?  
> **username_2**: I’m voting to close this question because it doesn't appear to be concerned with astronomy except tangentially.  
> **username_0**: Was going to post in astrology but fathomed the astronomy bros would understand better. Thanks my dudes  
> **username_3**: An astrologer's ephemeris is typically based on precise JPL data (i.e. taking into account eccentricity, perturbations etc), with the right ascension expressed in 30-degree segments of the circle (i.e. the astrological "signs"). If the software incorporates that JPL data, or any equivalent precise data, then this will resolve the eccentricity issue. There's no simple formula that will calculate a planet's apparent position (as seen from Earth) based on the planet's elliptical orbit *and* Earth's elliptical orbit *and* the orbital perturbations caused by Jupiter and/or nearby planets.  
> **username_3**: @JamesK You're absolutely correct that astrology questions don't belong here. However, this question is really about how to calculate a planet's right ascension, since that involves plotting the planet's position along the celestial equator which, by definition, is a circle. That seems perfectly on-topic to me. We shouldn't close a question merely because the science in the answer might be used for non-scientific purposes. I'm voting to leave the question open, although it could certainly do with some tighter wording.  

---

## 1 answers

### Answer by username_4 on 2020-06-11. Score: 0 | Accepted answer

If you already have a geocentric [ecliptic longitude](https://en.wikipedia.org/wiki/Ecliptic_coordinate_system), most likely no further correction is required.
When the ephemeris calculator computes each planet's heliocentric position (including Earth), it accounts for eccentricity by converting [mean anomaly](https://en.wikipedia.org/wiki/Mean_anomaly) to [true anomaly](https://en.wikipedia.org/wiki/True_anomaly).


---

