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871c26abde
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.
83 lines
3.2 KiB
Python
Executable File
83 lines
3.2 KiB
Python
Executable File
#!/usr/bin/env python3
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#
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# constellation.py - Don Cross - 2021-04-30 Fri
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#
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# Searches for the moon moving into different constellations.
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# This is an example of doing a search for the time of transition
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# of a body from one constellation to another.
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#
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import sys
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from astronomy import Time, Body, Constellation, ConstellationInfo, GeoVector, EquatorFromVector
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from typing import Tuple
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#------------------------------------------------------------------------------
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def BodyConstellation(body: Body, time: Time) -> ConstellationInfo:
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vec = GeoVector(body, time, False)
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equ = EquatorFromVector(vec)
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return Constellation(equ.ra, equ.dec)
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#------------------------------------------------------------------------------
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def FindConstellationChange(body: Body, c1: ConstellationInfo, t1: Time, t2: Time) -> Tuple[Time, ConstellationInfo]:
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# Do a binary search to find what time between t1 and t2
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# is the boundary between being in constellation c1 and some other
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# constellation. Return the tuple (tx, cx), where tx is the
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# transition time, and cx is the constellation we are moving into.
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tolerance = 0.1 / (24.0 * 3600.0) # one tenth of a second
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while True:
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dt = t2.ut - t1.ut
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tx = t1.AddDays(dt/2)
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cx = BodyConstellation(body, tx)
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if cx.symbol == c1.symbol:
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t1 = tx
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else:
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if dt < tolerance:
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# Always end the search inside the new constellation.
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return (tx, cx)
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t2 = tx
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#------------------------------------------------------------------------------
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def FindConstellationChanges(body: Body, startTime: Time, stopTime: Time, dayIncrement: float) -> int:
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t1 = startTime
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c1 = BodyConstellation(body, t1)
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while t1 < stopTime:
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t2 = t1.AddDays(dayIncrement)
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c2 = BodyConstellation(body, t2)
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if c1.symbol != c2.symbol:
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# The body moved from one constellation to another during this time step.
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# Narrow in on the exact moment by doing a binary search.
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tx, cx = FindConstellationChange(body, c1, t1, t2)
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print('{} : {} leaves {} and enters {}.'.format(tx, body.name, c1.name, cx.name))
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c1 = cx
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t1 = tx
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else:
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# No constellation change in this time step. Try again on the next time step.
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c1 = c2
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t1 = t2
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return 0
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#------------------------------------------------------------------------------
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if __name__ == '__main__':
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if len(sys.argv) == 1:
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startTime = Time.Now()
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elif len(sys.argv) == 2:
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startTime = Time.Parse(sys.argv[1])
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else:
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print('USAGE: {} [yyyy-mm-ddThh:mm:ssZ]'.format(sys.argv[0]))
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sys.exit(1)
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stopTime = startTime.AddDays(30.0)
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# There are 12 zodiac constellations, and the moon takes
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# about 27.3 days in its sidereal period. Therefore, there
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# are roughly 2.2 days per constellation. We will sample
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# the Moon's constellation once every 0.1 days to reduce
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# the chance of missing a brief transition through a small
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# part of a constellation.
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dayIncrement = 0.1
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rc = FindConstellationChanges(Body.Moon, startTime, stopTime, dayIncrement)
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sys.exit(rc)
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