Iam looking for Mean Anomaly at Epoch" J2000 for Venus

[ncc1701d]

hello,
I would like to get the "Mean Anomaly at Epoch" J2000 for Venus but confused by something
this link
https://in-the-sky.org/data/object.php?id=Venus
says "mean anomaly at epoch" venus is -64.56

https://en.wikipedia.org/wiki/Venus
says "mean anomaly" is 50.115 deg

Could someone explain why these would be so different?

I would like to get the "Mean Anomaly at Epoch" J2000 for Venus but surprised and unsure at that negative number so not sure where to get it.

I want to use it in the formula for Mean Anomaly (M)
M= Mo + n * ΔtJ2000
where mean motion venus = 1.60218
Mo is Mean Anomaly at Epoch
I just dont know what to use for Mo
thanks

 

[Keithth G]

Orbiter is itself quite a powerful ephemeris generator.

According to Orbiter's "Orbit MFD", the Mean Anomaly of Venus at epoch J2000 (ecliptic reference frame) is 50.11 degrees (to two decimal places of accuracy).



To get this value, open any scenario in Orbiter; then load up the Scenario Editor and adjust the date to 12:00:00 on 1st January 2000 (i.e., epoch J2000). Finally, open Orbit MFD and make the Sun the 'reference' and Venus the 'target'. On the right-hand side of the MFD display, there is a value labelled "MnA". This is Venus' Mean Anomaly for that date.

 

[ncc1701d]

Iam not experienced with Orbiter MFD but I got 50.10 and my circular graphic looks little different from yours Do you know why by looking at it?
I attached a pic of my MFD
I would prefer to get exactly what you got. thanks

 

[Keithth G]

Hi, ncc1701d

The key difference, I suspect, is that I have changed the default setting on the "Error limit" in the configuration files for the Sun and the planets from the default vale of 10^-6 (or variously 1-^-8) to a uniform 10^-11. According to 'martins', this forces Orbiter to use the full (and presumably more accurate) VSOP87 ephemeris rather than an abbreviated form of that ephemeris system that can be evaluated more quickly.

These configuration files are located in the 'config' directory and are variously called "Sun.cfg", "Mercury.cfg", "Venus.cfg" and so on. Try change the value of Error Limit to 10^-11 for all of the Sun and planetary configuration files and see if that makes a difference.

 

[ncc1701d]

thanks oddly enough after restarting orbiter this morning the numbers now match yours even with no error limit changes.
I might still change the error limits anyway.