By Patrick McCarthy, President, Astronomical Facts
My company web site has received a number of questions concerning facts about the Moon from students. I'll try to answer the most often asked questions in this article. If the data you are looking for is not included, please contact me via e-mail. I enjoy answering questions from students and the public.
Q: When does the First Quarter Moon Rise?
A: The First Quarter Moon is at a right angle to the line formed by the Sun and Earth. The First Quarter Moon will rise halfway between Sunrise and Sunset, basically at Noon.
Q: When does the Full Moon Rise?
A: The Sun, Earth and Moon form a strait line. The full face of the Moon is illuminated. The Full Moon rises as the Sun sets.
Q: How long is a day on the moon?
A: The Moon is tide locked, that means it does not rotate like the Earth. The same part of the Moon is always facing Earth. As the Moon orbits, or circles, the Earth the side facing the sun changes a little bit each day. From New Moon to New Moon, or one lunar cycle is the length of a day on the Moon, about 28 ¼ days.
Q: What are the phases of the Moon?
A: Most people know the moon's major phases, New, 1st Quarter, Full and Last Quarter but scientifically there are actually eight:
New Moon - Waxing Crescent - First Quarter - Waxing Gibbous - Full Moon - Waning Gibbous - Last Quarter - Waning Crescent.
Q: Waxing or waning, which is which?
A: Between the New Moon and the Full Moon the illuminated face of the Moon is growing larger, or waxing. After the Full Moon until the New Moon the illuminated face of the Moon is getting smaller so it is waning.
Q: Crescent Moon or Gibbous Moon, what do they mean?
A: The Crescent Moon, before the First Quarter or after the Last Quarter is when the face of the Moon is less than half illuminated. The Gibbous Moon is after the First Quarter to the Last Quarter (Except the day of the Full Moon) when more than half of the Moon's face is lighted by the Sun.
Mr. McCarthy is an expert in the calculation of astronomical data with over 20 years of experience as a Marine Navigator including six years on the staff of the Nautical Almanac Office of the U.S. Naval Observatory in Washington DC. He recently retired from the U.S. Naval Service and is President of Astronomical Facts, a technical service company providing calculations of astronomical information.
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