| MadSci Network: Earth Sciences |
Q:
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.
A:
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
bmendez@ssl.berkeley.edu
Try the links in the MadSci Library for more information on Earth Sciences.