The brightness of moonlight varies by approximately 3{½} stops of light between the first or last quarter and the full moon, based on the relative positions of the Earth, Sun, and Moon. Also, due to the elliptical orbits of the Moon around the Earth and the Earth around the Sun, lunar brightness can vary by as much as 30 percent, or another one-third of a stop. The opposition effect, which is caused by retroreflective properties (think cats' eyes) of the Moon's surface, may account for an increase in lunar brightness of another one-third to one-half of a stop when the Sun is almost directly behind the Earth, or in opposition to the Moon. Determining whether the Moon is near its apogee or perigee and the angle of incidence of the Earth and Sun relative to the Moon is relatively easy to accomplish with software for PDAs or from the Internet, but I find it unnecessary and distracting from the enjoyment of photographing the moonlit landscape. A more important consideration when photographing by moonlight is the Moon's angle of elevation above the horizon. In general, the higher the Moon is in the sky, the more illumination it will provide to the landscape. The Moon becomes a useful light source when it reaches about 30 degrees above the horizon. The Earth's atmospheric conditions can dramatically affect the intensity of moonlight reaching the surface of the Earth. It is fairly obvious that moonlight diffused by cloud cover will not only be dimmer than direct moonlight, but also softer and shadowless. It is less obvious that particles in the atmosphere, such as smog, dust, moisture, and even the air itself, can reduce moonlight intensity, especially when the Moon is near the horizon and the light must travel through considerably more atmosphere before it reaches the Earth. The difference in exposure when the Moon is directly overhead and when it is just above the horizon is about seven stops in clear, dry air; the difference is considerably more in moist or dusty air. This is because moonlight travels through 40 times more atmosphere when the Moon has just risen than when it is directly overhead. A simple illustration of this effect is the fact that it is possible to observe night photography the sunset by looking directly at the Sun, but you cannot look directly at the midday Sun without damaging your retinas. Also for this reason, higher altitudes and clear winter skies may lead to slightly shorter exposure times. photographing the FuLL moon When most people think of full moon photography, they understandably imagine taking pictures of the full moon. To the seasoned night photographer, however, full moon photography means photographing by the light of the Moon, which is a different thing altogether. If you want to include the Moon in your night photographs and record detail in the surface of the Moon while having a balanced overall exposure, you are generally limited to photographing on the actual day of the full moon, near moonrise and moonset, or by combining multiple exposures. This is the only time in the lunar cycle when the exposure for the Moon and surrounding landscape is approximately the same. It is very rare for the sunset and moonrise to occur at the exact same moment, and the two times can vary by as much as 30 or 40 minutes, even on the night of the full moon. The ideal photographic situation would be for the Sun to set about 10 minutes before moonrise. 196