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Earthsky Tonight - Oct 25 2009
Year's farthest first quarter moon October 25
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The moon reaches its first quarter phase tonight at 7:42 pm. Central Daylight Time (8:42 p.m. Eastern Daylight Time; 6:42 p.m. Mountain Daylight Time or 5:42 p.m. Pacific Daylight Time). At over 251,000 miles away, this is the farthest and smallest first quarter moon for all of 2009.
Quarter moon marks that fleeting moment when the moon is exactly 90 degrees from the sun on the sky’s dome. At quarter moon, half of the lunar disk is illuminated by sunlight, while the other half is covered over by the darkness of night. With the lunar month customarily starting at new moon, the first quarter moon marks the quarter point of the moon’s monthly orbit around Earth.
The month as measured by one complete cycle of the moon’s phases is called the lunar (or synodic) month. Most generally, the lunar month refers to the time period between sucessive new moons. However, the lunar month could also refer to the period between successive first quarter moons.
Farthest first quarter moons recur in cycles of 14 lunar months. After today’s first quarter moon, the 14th return to first quarter moon will fall on December 13, 2010. That will be the farthest and smallest first quarter moon for 2010!
Written by Bruce McClure
Comments (2)
at 11.34 pm on 10-25-2009 Tony
Bruce:
Can you explain with simple word what you said above about 14 lunar cycle? Thank you.
Replyat 06.57 am on 10-26-2009 Bruce McClure
Tony,
Are you asking for the name of this 14-lunar month cycle? I've seen it called the full moon cycle or fumocy. Fumocy is an abbreviation for full moon cycle.
One month as measured by the phases of the moon is called the lunar (or synodic) month. One month as measured by the moon's return to apogee (moon's farthest point from Earth) or perigee (moon's closest point to Earth) is called the anomalistic month. The lunar month = 29.53059 days and the anomalistic month = 27.55455 days. Therefore 14 lunar months almost exactly equal 15 anomalistc months.
14 x 29.53059 days = 413.428 days
15 x 27.55455 days = 413.318 days
Generally, this 14-lunar month cycle refers to the full moon realigning with perigee, not the first quarter moon realigning with apogee.
Bruce
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at 11.34 pm on 10-25-2009 Tony
Bruce:
Can you explain with simple word what you said above about 14 lunar cycle? Thank you.
at 06.57 am on 10-26-2009 Bruce McClure
Tony,
Are you asking for the name of this 14-lunar month cycle? I've seen it called the full moon cycle or fumocy. Fumocy is an abbreviation for full moon cycle.
One month as measured by the phases of the moon is called the lunar (or synodic) month. One month as measured by the moon's return to apogee (moon's farthest point from Earth) or perigee (moon's closest point to Earth) is called the anomalistic month. The lunar month = 29.53059 days and the anomalistic month = 27.55455 days. Therefore 14 lunar months almost exactly equal 15 anomalistc months.
14 x 29.53059 days = 413.428 days
15 x 27.55455 days = 413.318 days
Generally, this 14-lunar month cycle refers to the full moon realigning with perigee, not the first quarter moon realigning with apogee.
Bruce