MadSci Network: Earth Sciences

Re: How much light is reflected to N. Florida from a full moon in June

Date: Thu Jan 23 16:46:10 2003
Posted By: Bryan Mendez, Education and Public Outreach Scientist
Area of science: Earth Sciences
ID: 1042748905.Es

How much light is reflected to N. Florida from a full moon in June? I am trying to design an outdoor theater that utilizes moon light as the predominate form of light for the stage. I would appreciate information on how much light North Florida would receive in March and September as well-assuming a clear night. Thank you.

Hello Helen,
This sounds like a neat idea for a theater. As you mentioned the most critical thing affecting the illumination that the Moon could provide your theater is the weather conditions; you'll want clear skies for maximum illumination. The next critical thing to consider is the phase of the Moon. As the Moon orbits Earth we see it only part of its dayside hemisphere and the time at which it rises will change (it rises between 30-60 minutes earlier each day). Only during the Full Moon phase do we see the whole of the Moon's Sun-illuminated face. This occurs when the Moon is opposite in the sky from the Sun (thus it rises when the Sun sets). During the Full Moon is when you will receive maximum illumination from the Moon (which lasts for only a moment, but generally the night of the Full Moon is when it is brightest). The brightness of the Full Moon is 400,000 times less than the brightness of the noontime Sun, but still plenty bright to read by. The Day of the New Moon (which is roughly 2 weeks before and after the Full Moon) occurs when the Moon is directly between the Sun and Earth and we see none of the Moon's dayside. The Moon rises and sets with the Sun at this time and is not visible and so provides no illumination at night. In the two weeks between the New Moon and Full Moon, the Moon moves steadily farther East of the Sun in the sky and rises sometime after sunrise and so is in the sky for part of the daytime (and is visible) and part of the evening after sunset. The phase (and hence brightness) of the Moon also steadily grows from nothing during the New Moon to maximum during the Full Moon.  After the Full Moon the reverse happens. The Moon steadily decreases in brightness and phase for two weeks and is West of the Sun in the sky moving toward it day by day. During these two weeks the Moon is in the sky during the night and morning hours, rising progressively later until it rises with the Sun during the New Moon. Thus is the full cycle of phases of the Moon. The same phase and general rise and set times are seen as the same everywhere on Earth. So the Moon phase will be the same in Florida as it is in India. The exact time of rise and set of the Moon vary depending on latitude and the Moon's orbit (which is elliptical, inclined with respect to Earth's equator and orbit about the Sun, and precesses about in a 18.6 year cycle). These things are well known and can be found by using several websites that I have listed below or some commercial planetarium software such as The Sky, or Starry Night. The last thing you should be sure to consider is the angle of the Moon's illumination. If the Moon's path through the sky is too low it may not get high enough to directly illuminate your stage depending on how the theater is designed.

Okay, I hope this helps. You should check out the following links for specific information on Moon phases, rise and set times, and path through the sky for the location and dates you are considering for your performances.

Best of Luck,
Dr. Bryan Méndez, Education and Public Outreach Scientist, UC, Berkeley

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