Calculation of the position and rotation of the Earth’s orbit

Question

I want to calculate the position of the Earth (relative to the sun) and the rotation of the axis for a given date and time. It is good to assume that the Sun is motionless at 0,0,0 coordinates. Very slight deviations due to the gravitational gravity of the moon, for example, can also be ignored. Everything that is exactly within a degree or so is good enough.

Are there libraries / sources / data that will help me accomplish this?

Answer 1

The aa-56 code, which can be downloaded here , includes solar ephemeris that are likely to meet your needs. For precision work, you need something more accurate, like the JPL DE421, but there are some uncomfortably large conversion tables, and this is probably a bust if you are happy with 1 degree accuracy.

Earth's rotation at a given time is given by stellar time in Greenwich.
Jean Mius "Astronomical Algorithms" (a good reference to these kinds of calculations!) Gives a formula for theta0(cumulative rotation angle in degrees) in terms of Julian date JD:

T = (JD - 2451545.0 ) / 36525

theta0 = 280.46061837 + 360.98564736629*(JD-2451545.0) + 
           0.000387933*T*T - T*T*T/38710000.0

theta0 = 0 degrees mod 360 represents the moment when the Greenwich meridian is aligned with a right ascension of 0:00 in celestial coordinates.

Answer 2

. Ephemeris.

JPL - Ephemeris, , , , .

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Answer 3

Python, ephem:

>>> import ephem
>>> sun = ephem.Sun()
>>> sun.compute(ephem.now())
>>> sun.hlong, sun.hlat, sun.earth_distance
(69:41:32.6, 0:00:00.2, 0.98602390289306641)

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