Accurate RA and DEC

  • Thread starter Philosophaie
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In summary, r, v, w, and N are computed from JPL data and then used to calculate the Sun's position in both ecliptic and equatorial coordinate systems. The equation provided is true for finding the Sun's RA and DEC, but only within certain ranges for the ecliptic longitude and latitude.
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Philosophaie
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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.
 
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  • #2
Yes, the equation you provided is true. However, you have to keep in mind that the RA and DEC values you get from this equation are only correct if the ecliptic longitude (lonsun) is in the range 0-360 degrees and the ecliptic latitude (latSun) is in the range -90-90 degrees. For example, if your ecliptic longitude is greater than 360 degrees or your ecliptic latitude is outside of the specified range, then the RA and DEC values you get from this equation will be incorrect.
 

1. What is RA and DEC?

RA and DEC stand for right ascension and declination, respectively. These are celestial coordinates used to locate objects in the sky.

2. How is RA and DEC measured?

RA is measured in hours, minutes, and seconds, while DEC is measured in degrees, minutes, and seconds. They are measured relative to the celestial equator and the vernal equinox.

3. What is the difference between RA and DEC?

RA measures the east-west position of an object in the sky, while DEC measures the north-south position. Together, they provide the precise location of an object in the celestial sphere.

4. Why is accurate RA and DEC important?

Accurate RA and DEC are important for astronomers to locate and track objects in the sky, as well as for navigation purposes. They also allow for precise measurements and comparisons between different celestial objects.

5. How is accurate RA and DEC determined?

Accurate RA and DEC are determined using specialized telescopes and instruments that can accurately measure the positions of celestial objects. These measurements are then compared to known catalogs and databases to determine the precise coordinates.

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