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Use mypy to check all Python demo programs. Updated the demos to pass type checking. There were a couple of small mistakes found, so this was worth the effort.
70 lines
2.7 KiB
Python
Executable File
70 lines
2.7 KiB
Python
Executable File
#!/usr/bin/env python3
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#
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# jupiter_moons.py - by Don Cross - 2021-04-15
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#
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# Example Python program for Astronomy Engine:
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# https://github.com/cosinekitty/astronomy
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#
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# Calculates the coordinates of Jupiter and its four major moons
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# (Io, Europa, Ganymede, and Callisto) as seen from the Earth
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# at a given date and time. This program illustrates how to correct
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# for the delay caused by the time it takes for light to reach
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# the Earth from the Jupiter system.
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#
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import sys
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from astronomy import Time, JupiterMoons, GeoVector, EquatorFromVector, Body, C_AUDAY, Vector
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def PrintBody(name: str, geovec: Vector) -> None:
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# Convert the geocentric vector into equatorial coordinates.
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equ = EquatorFromVector(geovec)
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print('{:<8s} RA {:10.6f} DEC {:10.6f} {:10.6f} AU'.format(name, equ.ra, equ.dec, equ.dist))
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if __name__ == '__main__':
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# If date/time is provided on the command line, use it.
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# Otherwise, use the current date and time.
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if len(sys.argv) == 2:
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time = Time.Parse(sys.argv[1])
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else:
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time = Time.Now()
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print('Calculations for:', time)
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# Call GeoVector to calculate the geocentric position of Jupiter.
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# GeoVector corrects for light travel time.
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# That means it returns a vector to where Jupiter appears to be
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# in the sky, when the light left Jupiter to travel toward the
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# Earth to arrive here at the specified time. This is different from
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# where Jupiter is at that time.
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jv = GeoVector(Body.Jupiter, time, True)
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# Calculate the amount of time it took light to reach the Earth from Jupiter.
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# The distance to Jupiter (AU) divided by the speed of light (AU/day) = time in days.
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lt_days = jv.Length() / C_AUDAY
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print()
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print('It took light {:0.2f} minutes to reach the Earth from Jupiter.'.format(lt_days * 24.0 * 60.0))
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print()
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# The JupiterMoons function calculates positions of Jupiter's moons without
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# correcting for light travel time. Correct for light travel by backdating
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# by the given amount of light travel time.
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backdate = time.AddDays(-lt_days)
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jm = JupiterMoons(backdate)
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# Tricky: I'm "cheating" a little bit below by adding Vector `jv`
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# to StateVector `jm.<moon>`, to result in a Vector position for each moon.
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# This works because StateVector has all the fields that Vector has,
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# plus the velocity components (vx, vy, vz).
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# This is alarming to type purists, but just another normal day of
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# "duck typing" for Pythonistas.
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PrintBody('Jupiter', jv)
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PrintBody('Io', jv + jm.io.Position())
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PrintBody('Europa', jv + jm.europa.Position())
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PrintBody('Ganymede', jv + jm.ganymede.Position())
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PrintBody('Callisto', jv + jm.callisto.Position())
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print()
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sys.exit(0)
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