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Challenge 60: Space Week Day 6: Moon Phase

curriculum/challenges/english/blocks/daily-coding-challenges-python/68c497f3aaefc9fd9f1b0e24.md

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--description--

For day six of Space Week, you will be given a date in the format "YYYY-MM-DD" and need to determine the phase of the moon for that day using the following rules:

Use a simplified lunar cycle of 28 days, divided into four equal phases:

  • "New": days 1 - 7
  • "Waxing": days 8 - 14
  • "Full": days 15 - 21
  • "Waning": days 22 - 28

After day 28, the cycle repeats with day 1, a new moon.

  • Use "2000-01-06" as a reference new moon (day 1 of the cycle) to determine the phase of the given day.
  • You will not be given any dates before the reference date.
  • Return the correct phase as a string.

Note: Day 1 represents the day of the new moon, meaning 0 days have passed since the last new moon.

--hints--

moon_phase("2000-01-12") should return "New".

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(moon_phase("2000-01-12"), "New")`)
}})

moon_phase("2000-01-13") should return "Waxing".

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(moon_phase("2000-01-13"), "Waxing")`)
}})

moon_phase("2014-10-15") should return "Full".

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(moon_phase("2014-10-15"), "Full")`)
}})

moon_phase("2012-10-21") should return "Waning".

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(moon_phase("2012-10-21"), "Waning")`)
}})

moon_phase("2022-12-14") should return "New".

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(moon_phase("2022-12-14"), "New")`)
}})

--seed--

--seed-contents--

py
def moon_phase(date_string):

    return date_string

--solutions--

py
from datetime import datetime
def moon_phase(date_string):
    ref_date = datetime.strptime("2000-01-06", "%Y-%m-%d")
    target_date = datetime.strptime(date_string, "%Y-%m-%d")

    diff_days = (target_date - ref_date).days
    cycle_day = (diff_days % 28) + 1

    if cycle_day <= 7:
        return "New"
    elif cycle_day <= 14:
        return "Waxing"
    elif cycle_day <= 21:
        return "Full"
    else:
        return "Waning"