Eris possition wrong

[Martin Lewicki]

Positon of Eris in 0.10.1 is wrong. Does not match NASA

I can't make sense of some of the orbital element entries in ssytem.ini for Eris. A mess format. Tried various ways of putting Eris elements from NASA Small-Body Database to no avail - still wrong position.

http://ssd.jpl.nasa.gov/horizons.cgi

http://ssd.jpl.nasa.gov/sbdb.cgi#top

Marty

[barrykgerdes]

I am using

[eris]
name = Eris
parent = Sun
radius = 1300
oblateness = 0.0
albedo = 0.689
lighting = true
orbit_visualization_period = 204376.01809
halo = true
color = 1.0,1.0,1.0
rot_periode = 8
tex_halo = star16x16.png
tex_map = nomap.png
coord_func = comet_orbit
orbit_Epoch = 2454800.50
orbit_MeanAnomaly = 198.858225
orbit_SemiMajorAxis = 67.902798
orbit_Eccentricity = 0.4361532
orbit_ArgOfPericenter = 151.51961
orbit_AscendingNode = 35.95741
orbit_Inclination = 44.022944

This appears to be tha latest informaton

This apparently earlier data

[eris]
name = Eris
parent = Sun
radius = 1300
oblateness = 0.0
albedo = .689
lighting = true
orbit_visualization_period = 203603
halo = true
color = 1.0,1.0,1.0
tex_halo = star16x16.png
tex_map = nomap.png
coord_func = comet_orbit
orbit_Epoch = 2454200.5
orbit_MeanAnomaly = 197.96
orbit_SemiMajorAxis = 67.732
orbit_Eccentricity = 0.4400
orbit_ArgOfPericenter = 151.56
orbit_AscendingNode = 35.8844
orbit_Inclination = 44.1595

Puts Eris about 5 arc secs further north

Barry

[barrykgerdes]

Hi Hendrik and Martin

The svn has now been updated with the revised data for Eris Using the later parameters provided by Hendrik. Which seems to give the correct results. Certainly near enough to locate in a 1 arc minute field

Barry

[barrykgerdes]

The orbital elements in the ssystem.ini file were obtained some time ago and could be way out particularly with the ell_orbit algorithm. I entered the orbital params from the reference and this placed Eris at 2hr18m41.3s +1d10m9.5s but I cannot confirm where it actually is.

Barry

[Kird]

Try these values for the orbital elements:

[eris]
name = Eris
parent = Sun
radius = 1300
oblateness = 0.0
albedo = 0.367
lighting = true
orbit_visualization_period = 204376.01809
halo = true
color = 1.0,1.0,1.0
rot_periode = 8
tex_halo = star16x16.png
tex_map = nomap.png
coord_func = ell_orbit
orbit_Epoch = 2454800.50
orbit_SemiMajorAxis = 67.902798
orbit_Eccentricity = 0.4361532
orbit_Inclination = 44.022944
orbit_AscendingNode = 35.95741
orbit_LongOfPericenter = 151.51961
orbit_MeanLongitude = 198.858225

[barrykgerdes]

Hi Kird

They are almost the same as what I have
Where does that put Eris at the moment

Barry

[Blake Nancarrow]

"Almost" counts in horse shoes!

[Kird]

I didn't notice, but the section for Eris is completely messed up.
The names for the orbital elements are wrong. It should be:
[eris]
name = Eris
parent = Sun
radius = 1300
oblateness = 0.0
albedo = 0.367
lighting = true
orbit_visualization_period = 204376.01809
halo = true
color = 1.0,1.0,1.0
rot_periode = 8
tex_halo = star16x16.png
tex_map = nomap.png
coord_func = comet_orbit
orbit_Epoch = 2454800.50
orbit_MeanAnomaly = 198.858225
orbit_SemiMajorAxis = 67.902798
orbit_Eccentricity = 0.4361532
orbit_ArgOfPericenter = 151.51961
orbit_AscendingNode = 35.95741
orbit_Inclination = 44.022944

This puts Eris in Cetus near Mira (though you have to zoom in a million times to see Mira).
I'm not sure about the coord_func. Should it be el_orbit or comet_orbit?

Hendrik

[Kird]

It's comet_orbit. When you use ell_orbit Eris is behind the Sun ans stays there, even when you change the date.

[barrykgerdes]

Hi Hendrik

Using your ellements in comet_orbit puts Eris at 1hr37m17.5s
-4d38m36s

I used the elements from the reference in ell_orbit and got Eris at 2hr18m41.3s +1d10m9s

I noted that ell_orbit with your params centres on the sun.

What I don't know is the true position for Eris. I haven't found a site that gives them yet.

Here is what I used

[eris]
name = Eris
parent = Sun
radius = 1300
oblateness = 0.0
albedo = 0.367
lighting = true
orbit_visualization_period = 2.041162179748626E+05
halo = true
color = 1.0,1.0,1.0
rot_periode = 8
tex_halo = star16x16.png
tex_map = nomap.png
coord_func = ell_orbit
orbit_Epoch = 2456282.469734213620
orbit_Period = 2.04376018098831855955E+05
orbit_SemiMajorAxis = 9.751882097335734E+9
orbit_Eccentricity = 4.361532020451209E-01
orbit_Inclination = 6.790279813775292E+01
orbit_AscendingNode = 3.828677530214852E+01
orbit_LongOfPericenter = 198.858250539009
orbit_MeanLongitude = 35.95740654774798

Barry

[Kird]

I got these values from the NASA site as Martin had looked there. But in my opinion the best site for orbital elements (for asteroids and for comets) is the Minor Planet Center.

http://www.cfa.harvard.edu/iau/Ephemerides/index.html

http://www.cfa.harvard.edu/iau/Ephemerides/Distant/D6199.html

http://www.cfa.harvard.edu/iau/Ephemerides/Comets/index.html

http://www.cfa.harvard.edu/iau/mpc.html

http://www.cfa.harvard.edu/iau/info/OrbElsExplanation.html

[Kird]

This ephemeris is from the MPC-site. R.A. 1 37 and Dec -04 38 are the right values.

Date TT R. A. (2000) Decl. Delta r Elong. Phase V
2009 02 08 01 36.91 -04 43.8 97.184 96.730 62.3 0.5 18.8
2009 02 13 01 37.00 -04 42.4 97.256 96.729 57.5 0.5 18.8
2009 02 18 01 37.10 -04 41.0 97.325 96.728 52.7 0.5 18.8
2009 02 23 01 37.22 -04 39.5 97.388 96.728 47.9 0.4 18.8
2009 02 28 01 37.35 -04 38.0 97.447 96.727 43.2 0.4 18.8
2009 03 05 01 37.49 -04 36.5 97.500 96.726 38.6 0.4 18.8
2009 03 10 01 37.64 -04 35.0 97.547 96.726 34.0 0.3 18.8

These positions agree with those from other sites and other planetarium programs.

Hendrik

[barrykgerdes]

Yes those positions agree with this

[eris]
name = Eris
parent = Sun
radius = 1300
oblateness = 0.0
albedo = .689
lighting = true
orbit_visualization_period = 203603
halo = true
color = 1.0,1.0,1.0
tex_halo = star16x16.png
tex_map = nomap.png
coord_func = comet_orbit
orbit_Epoch = 2454200.5
orbit_MeanAnomaly = 197.96
orbit_SemiMajorAxis = 67.732
orbit_Eccentricity = 0.4400
orbit_ArgOfPericenter = 151.56
orbit_AscendingNode = 35.8844
orbit_Inclination = 44.1595

Barry