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43 lines
1.4 KiB
Python
43 lines
1.4 KiB
Python
#
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# Copyright (c) 2009-2015 Tom Keffer <tkeffer@gmail.com>
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#
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# See the file LICENSE.txt for your full rights.
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#
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"""Determine the phase of the moon phase given a date.
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CF: http://en.wikipedia.org/wiki/Lunar_phase
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"""
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import datetime
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import math
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import decimal
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dec = decimal.Decimal
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moon_phases = ["new (totally dark)",
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"waxing crescent (increasing to full)",
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"in its first quarter (increasing to full)",
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"waxing gibbous (increasing to full)",
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"full (full light)",
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"waning gibbous (decreasing from full)",
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"in its last quarter (decreasing from full)",
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"waning crescent (decreasing from full)"]
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def moon_phase(year, month, day):
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"""Calculates the phase of the moon, given a year, month, day.
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returns: a tuple. First value is an index into an array
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of moon phases, such as Moon.moon_phases above. Second
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value is the percent fullness of the moon.
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"""
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time_dt = datetime.datetime(year, month, day)
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diff = time_dt - datetime.datetime(2001, 1, 1)
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days = dec(diff.days) + (dec(diff.seconds) / dec(86400))
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lunations = dec('0.20439731') + (days / dec('29.530589'))
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position = float(lunations) % 1.0
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fullness = int(100.0*(1.0 - math.cos(2.0 * math.pi * position))/2.0 + 0.5)
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index = int((position * 8) + 0.5) & 7
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return (index, fullness)
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