Here were the orbital elements of 2005 YU55 at 12h UT on 27 August 2011.
Semimajor axis, a.
a = 1.142716307446735 AU
Eccentricity, e.
e = 0.4289483227642857
Inclination to ecliptic, i.
i = 0.5134565690566446°
Longitude of ascending node, Ω.
Ω = 39.31611122146938°
Argument of the perihelion, Ï.
Ï = 268.7740217096003°
Time of perihelion passage, T.
T = JD 2455814.319486848290 = 9 September 2011 at 7:40:04 UT
The mean anomaly, the eccentric anomaly, and the true anomaly, are time-dependent angles. They change as time passes. You need to calculate what they will be at any particular moment in time, as part of reducing the orbital elements to a position vector in heliocentric ecliptic coordinates.
I'll show you how that's done.
t = the moment, in Julian Date format, at which the heliocentric position of the planet is desired to be known.
Find the period, P, of the asteroid's orbit around the sun, in days.
P = (365.256898326 days) a^1.5
Find the mean anomaly, m, in radians.
m₀ = (t â T) / P
m = 2Ï [ m₀ â integer(m₀) ]
Find the eccentric anomaly, u, in radians. The Danby first approximation for the eccentric anomaly, u, in radians.
u' = m + (e â e³/8 + e⁵/192) sin(m) + (e²/2 â e⁴/6) sin(2m) + (3e³/8 â 27e⁵/128) sin(3m) + (e⁴/3) sin(4m)
The Danby's method refinement for the eccentric anomaly.
u = u'
Repeat...
. U = u
. F₀ = U â e sin U â m
. F₁ = 1 â e cos U
. F₂ = e sin U
. F₃ = e cos U
. D₁ = âF₀ / F₁
. D₂ = âF₀ / [ F₁ + D₁ F₂ / 2 ]
. D₃ = âF₀ / [ F₁ + D₁ F₂ / 2 + D₂² F₃ / 6 ]
. u = U + D₃
UNTIL |uâU| < 1e-14
Note that you will need to adjust the error tolerance (shown above as 1e-14) to be appropriate for the precision of your variables, if you are using machine calculation.
Find the canonical position vector of the object in its orbit at time t.
x''' = a (cos u â e)
y''' = a sin u â(1âe²)
z''' = 0
Find the true anomaly, θ. We'll use it below when we find the velocity.
θ = Arctan( y''' , x''' )
Definition of the two-argument Arctan function.
atn(z) = single argument Arctan function of the argument z.
Function Arctan( y , x )
. if x = 0 and y > 0 then angle = +Ï/2
. if x = 0 and y = 0 then angle = 0
. if x = 0 and y < 0 then angle = âÏ/2
. if x < 0 then angle = atn(y/x) + Ï
. if x > 0 and y > 0 then angle = atn(y/x)
. if x > 0 and y < 0 then angle = atn(y/x) + 2Ï
Arctan = angle
Rotate the triple-prime position vector by the argument of the perihelion, Ï.
x'' = x''' cos Ï â y''' sin Ï
y'' = x''' sin Ï + y''' cos Ï
z'' = z''' = 0
Rotate the double-prime position vector by the inclination, i.
x' = x''
y' = y'' cos i
z' = y'' sin i
Rotate the single-prime position vector by the longitude of the ascending node, Ω.
x = x' cos Ω â y' sin Ω
y = x' sin Ω + y' cos Ω
z = z'
The unprimed position vector [x,y,z] is the position in heliocentric ecliptic coordinates.
Find the canonical (triple-prime) heliocentric velocity vector.
k = â{ GM / [ a AU (1 â e²) ] }
k is a speed in meters per second.
GM = 1.32712440018e20 m³ sec⁻²
AU = 1.49597870691e11 m au⁻¹
Vx''' = âk sin θ
Vy''' = k (e + cos θ)
Vz''' = 0
Rotate the triple-prime velocity vector by the argument of the perihelion, Ï.
Vx'' = Vx''' cos Ï â Vy''' sin Ï
Vy'' = Vx''' sin Ï + Vy''' cos Ï
Vz'' = Vz''' = 0
Rotate the double-prime velocity vector by the inclination, i.
Vx' = Vx''
Vy' = Vy'' cos i
Vz' = Vy'' sin i
Rotate the single-prime velocity vector by the longitude of the ascending node, Ω.
Vx = Vx' cos Ω â Vy' sin Ω
Vy = Vx' sin Ω + Vy' cos Ω
Vz = Vz'
The unprimed velocity vector [Vx,Vy,Vz] is the sun-relative velocity in ecliptic coordinates.