Calculating the Earth's Elliptical Orbit around the Sun

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Discussion Overview

The discussion revolves around calculating the Earth's elliptical orbit around the Sun, focusing on the parameters involved in the calculations, particularly the true anomaly and eccentric anomaly. Participants are sharing equations and methods, as well as questioning the accuracy of existing data and calculations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant mentions the need for Excel VBA expertise to calculate the Earth's orbit and provides a link to JPL's data for reference.
  • Another participant points out an error in the equation for calculating the eccentric anomaly and claims that the true anomaly is an increasing function of time.
  • A different participant suggests starting the true anomaly at 210 degrees and questions the uniformity of its increase over time.
  • One participant asserts that the true anomaly should start at the Summer Solstice and challenges the calculations presented in the table.
  • Another participant disputes the claim about the initial value of the true anomaly and explains that it does not increase uniformly, citing perihelion and apohelion dynamics.
  • One participant expresses uncertainty about their own equations and seeks confirmation on the correctness of their calculations for the argument of perihelion, mean longitude, mean anomaly, and eccentric anomaly.
  • A later reply discusses the Earth's proximity to the Sun during winter, indicating a tilt away from the Northern Hemisphere.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the calculations and interpretations of the true and eccentric anomalies. The discussion remains unresolved with no consensus on the accuracy of the equations or the initial conditions for the true anomaly.

Contextual Notes

Participants highlight various assumptions and potential inaccuracies in the calculations, including the treatment of mean anomaly and the timing of true anomaly increases. There are references to the differences between tropical and sidereal years, as well as the implications of orbital dynamics on true anomaly changes.

Philosophaie
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To help me you will need tho know Excel VBA very well.

Earth has an elliptical orbit around the sun. JPL's website has the data to calculate this orbit:
http://ssd.jpl.nasa.gov/txt/p_elem_t1.txt
In the spreadsheet the parameters are calculated from widely used equations and some of my making. The major discrepencies are in how to calculate the distance between the Earth and the Sun,r. By my calculations:
r<1AU and a minimum @True Anomaly=0
r>1AU and a maximum @True Anomaly=180
This is not the case when directly calculated from the table(In Green). My calculations of what they should be are in yellow.

Any suggestions would be deeply appreciated!
 

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Astronomy news on Phys.org
Your equation for calculating the eccentric anomaly is incorrect:
Code:
  Do
     E1 = E0 - (E0 - e(k) * 180 / Pi * Math.Sin(E0) - MA(k)) / (1 - e(k) * Math.Cos(E0))
   Loop While E1 = E0
   EA(k) = E1

Your input values for the true anomaly (column M) are completely wrong. True anomaly is an increasing function of time, not decreasing, and it is not uniform in time.
 
If I change the values of the True Anomaly to increase by starting with 210,240,270,300,330,0,30,60,90,120,150,180 that would be increasing and will still prove my point.
I got the Eccentric Anomaly from this website:
http://www.stjarnhimlen.se/comp/tutorial.html
If I may, does anyone have a better equation for Eccentric Anomally?
 
Here is the corrected True Anomaly with increasing degrees in E and M. The True, Mean and Eccentric Anomaly increase each year by about 360 degrees making a wrap around function. I think that the True Anomaly v=0 should start @Jun 21 the Summer Solstice not at v=168.0600083 as calculated from the table. I think the calculations of M and E from the table (in Green) are wrong.
 

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Philosophaie said:
If I change the values of the True Anomaly to increase by starting with 210,240,270,300,330,0,30,60,90,120,150,180 that would be increasing
What makes you think the initial value is 210? (Hint: It isn't.) What makes you think the true anomaly increases by 30 degrees per month? (Hint: It doesn't.)

... and will still prove my point.
What is your point, exactly? That you posted this in the "Beyond the Standard Model" section makes me think your point might be some crackpot theory. I hope that that is not the case.

I got the Eccentric Anomaly from this website:
http://www.stjarnhimlen.se/comp/tutorial.html
If I may, does anyone have a better equation for Eccentric Anomally?
There are two things wrong with your Newton's method implementation. (1) You are treating the mean anomaly as if it were in radians. (2) Your loop condition is wrong. As written, the loop will only execute once.
 
Philosophaie said:
I think that the True Anomaly v=0 should start @Jun 21 the Summer Solstice not at v=168.0600083 as calculated from the table. I think the calculations of M and E from the table (in Green) are wrong.
You're wrong. In 2008, for example, perihelion occurred on January 3. True anomaly does not increase by exactly 30 degrees per month, for several reasons.
  1. No month is 365.25/12 days long.
  2. You are confusing the tropical year (solstice to solstice) and the sidereal year (apsis to apsis). The sidereal year is 20 minutes and 24 seconds longer than the tropical year.
  3. True anomaly is not a uniform function of time. Think of it in terms of a comet's orbit. Near apohelion, the true anomaly changes very little from day to day, while near perihelion, the true anomaly changes very rapidly.
 
My equations (in Yellow) are just my way of trying to understand, PLEASE DISREGARD. The main equations (in Green) are what need to be correct then comes understanding. Are these equations correct?
'Argument of the Perihelion
PA(k) = LP(k) - LAN(k)
'Mean Longitude of Earth at a particular time
ML(k) = .Cells(7, 5) + .Cells(8, 5) * JT(k)
ML(k) = ML(k) - 360 * Int(ML(k) / 360)
'Mean Anomaly of Earth at a particular time
MA(k) = ML(k) - LP(k)
MA(k) = MA(k) - 360 * Int(MA(k) / 360)
'Eccentric Anomaly of Earth at a particular time from above website
EA(k) = MA(k) + 180 / Pi * e(k) * Math.Sin(MA(k) * Pi / 180) * (1 + e(k) * Math.Cos(MA(k) * Pi / 180))
EA(k) = EA(k) - 360 * Int(EA(k) / 360)
 
Last edited:
So in the winter, say Jan 3, the Earth is closer to the sun just tilted away from the Northern Hemisphere.
 

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