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Accurate RA and DEC

  1. Apr 4, 2010 #1
    Could someone do an equation check:

    r,v,w and N are computed from JPL data

    Sun's true longitude:
    lonsun = v + w

    Convert lonsun,r to ecliptic rectangular geocentric coordinates xs,ys:
    xecl = r * cos(lonsun)
    yecl = r * sin(lonsun)

    (since the Sun always is in the ecliptic plane, zs is of course zero). xs,ys is the Sun's position in a coordinate system in the plane of the ecliptic. To convert this to equatorial, rectangular, geocentric coordinates, compute:
    xequ = xecl
    yequ= yecl * cos(ecl)
    zequ = yecl * sin(ecl)

    Finally, compute the Sun's Right Ascension (RA) and Declination (Dec):
    RA = atan2( yequ, xequ )
    Dec = atan2( zequ, sqrt(xequ*xequ+yequ*yequ) )

    I have been using:

    xecl = (Cos(w) *Cos(N) -Sin(w) *Sin(N) * Cos(i)) * x(k) + (-Sin(w) *Cos(N) - Cos(w) *Sin(N) *Cos(i)) * y
    yecl = (Cos(w) * Sin(N) -Sin(w) *Sin(N) *Cos(i) * x + (Sin(w) * Sin(N) -Cos(w) * Cos(N) *Cos(i) )* y
    zecl(k) = (Sin(w) * Sin(i)) * x + (Cos(w) *Sin(i)) * y

    xeq = xecl(k)
    yeq = Cos(oe) * yecl - Sin(oe) * zecl
    zeq = Sin(oe) * yecl + Cos(oe) * zecl
    where oe is the obiliqity of the planet

    also RA=N+W+v is the equation true.

    Looking for an accurate RA and DEC derived from JPL data.
    Last edited: Apr 5, 2010
  2. jcsd
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