The Moon is a satellite of the Earth, shining by the reflected light of the Sun. At a distance of about 384,399 kilometers (238,854 miles) on average, it orbits around the Earth about once a month (29.5305882 days). The Moon is our closest neighbor in space and the second brightest object in the sky after the Sun. As the Moon orbits the Earth, the geometry between the Sun, Moon and Earth changes, causing different phases of illumination on the Moon. When the Moon is close to the Sun in the sky it is hidden in the Sun's glare and not visible. This is called a "new" Moon. The phases the Moon goes through are: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent, and back to new. First and third quarter moons are sometimes called "half" moons because they are side-lit and only 1/2 of the visible face of the Moon is illuminated. The Moon has a diameter of about 3,474 kilometers (2,158 miles). This about one quarter of the Earth's diameter of 12,756 kilometers (7,926 miles). The Moon is quite large in relation to the Earth compared to the moons of other planets in the Solar system. The current best theory on the origin of the Moon is that it formed after a giant collision between the Earth and another planetary body early in the formation of the solar system some 4.5 billion years ago. This collision threw out debris from the Earth that went into orbit around the Earth and formed the Moon. The Moon is tidally locked as it orbits around the Earth. This is why we always see the same face of the Moon and can't see the far side from Earth. There is a slight variability to this called libration, where we can see slightly more around the edges of the Moon during a full lunation ( the period of time from one new moon to the next - a lunar month). In all, we can see about 59 percent of the total lunar surface from Earth. The side of the Moon that faces the Earth shows large dark areas called Maria, and light heavily cratered highlands. These are mostly what we see when we look at the Moon with our unaided eyes. Maria are the circular remnants of large impacts that occurred early in the life of the Moon, and which later filled with dark lava from volcanic activity. This volcanic activity has long since ended on the Moon. One of the things that makes the Moon so fascinating visually, and in photographs, is that its surface is covered by craters left behind from the impacts of asteroids, comets and meteoroids. The Earth has been bombarded by these objects as well, but because of the active geology and weather of the Earth, most of these scars have eroded away. On the Moon there is little active geology and no weather, so the scars last a long time. Also many of the smaller objects that burn up in the Earth's atmosphere don't reach the ground to impact. Since the Moon doesn't have an atmosphere, none of these smaller objects burn up, so they crash onto the Moon's surface. These small impacts are still happening, even today, and have been observed by amateur and professional astronomers. These craters are a record of the violent history of the solar system. Lunar Eclipses Sometimes as it orbits around the Earth, the Moon will happen to pass through the shadow of the Earth. When this happens, the Earth blocks the Sun's light from shining on the full Moon and a total or partial lunar eclipse occurs.
The shadow of the Earth is comprised of two parts, the umbra and penumbra. The umbra is the darkest part where all of the Sun's light is blocked. The penumbra is where only part of the Sun's light is blocked. When the Moon passes through the Earth's shadow it may not fully pass through the umbra, and a partial lunar eclipse occurs. Although the direct light of the Sun is blocked completely during a total lunar eclipse, some light still refracts through the Earth's atmosphere to subtly illuminate the Moon. Because it is filtered by the Earth's atmosphere, which scatters blue light, the light that reaches the Moon is a burnt orange or red color. If you could stand on the Moon during a total lunar eclipse, you would see the Earth slowly block out the light of the Sun, and then you would see a thin red ring of light all the way around the Earth. This fiery ring is the light of all the sunrises and sunsets taking place around the edge of the entire world at the time of the eclipse. The brightness of the Moon during totality is affected by the amount of dust and clouds in the Earth's atmosphere around the edge at the time of the eclipse. A clear atmosphere produces a bright eclipse. An atmosphere full of volcanic ash and dust can cause a very dark eclipse. After some volcanic eruptions, such as Mount Pinatubo in 1992 and El Chichon in 1982, the following total lunar eclipses were so dark that the Moon was almost invisible to the unaided eye. Earthshine One of the most beautiful phenomenon that can be seen on the Moon is that of Earthshine.
Earthshine can be seen on the "dark", or unlit, side of the Moon when the Moon is in a crescent phase. The thinner the crescent, the more prominent the Earthshine can be. Direct light from the Sun illuminates the crescent portion of the Moon. We see this light reflected directly from the Sun to the Moon to our eyes.
Earthshine that illuminates the rest of the Moon comes from sunlight that is reflected off the Earth to the Moon and then back to our eyes. This double reflection greatly reduces the amount of light, so the Earthshine portion of the Moon is much fainter than the brilliant crescent portion. The difference in illumination is so great that detail in both the sunlit-illuminated crescent and Earthshine-illuminated portions can't be captured in a single exposure with a normal digital camera. High-dynamic range techniques can be used to show details in both however. Craters, Mountains, Valleys, Rilles There are many fascinating things to see and photograph in high-resolution on the surface of the Moon such as craters, mountains and rilles.
Craters are basically holes left behind after something like an asteroid crashed into the Moon. These impacts can be small, or huge, throwing ejecta all over the lunar surface, such as around the lunar crater Tycho. Craters were first discovered, and named, by Galileo when he turned his telescope on the Moon for the first time on November 30, 1609. Because there is little erosion on the Moon, some craters are as old as two billion years.
Mountains on the Moon were formed by geologic processes and around the edges of impacts. Some peaks in the middle of larger craters are formed by material welling back up after an impact in a splash effect. Mountains can be found in groups or ranges (Montes), or standing alone (Mons). The Apennines (Montes Appenninus) is one of the highest mountain ranges on the Moon and can be found on the southeastern edge of the Imbrium basin. Valleys can also be seen between mountains and mountain ranges on the Moon. Most valleys are found in the highlands of the Moon. The two largest are the great Alpine Valley (Vallis Alps) and Rheita Valley (Vallis Rheita). The Alpine Valley is located in the Alpine range between Mare Imbrium and Mare Frigoris. It is about 10 km (6.2 miles) wide and 180 km (112 miles) wide. The Rheita Valley can be found in the southeastern highlands, and is 30 km wide (15.5 miles) and 445 km (276 miles) long.
Lunar Rilles (called Rima in the Latin, and Rimae in the plural) are long narrow depressions that resemble channels. They are usually only a few kilometers wide, but can be hundreds of kilometers long. Their formation is usually related to ancient volcanic activity or collapsed sections of crust between two lunar faults, called graben. The largest graben rille is the Vallis Alpes, which has a smaller rille running through it. Rilles can be challenges for high-resolution photography. Schroter's Valley (Vallis Schröteri) in Oceanus Procellarum is the largest sinuous rille on the Moon. Other fascinating rilles are Rupes Recta in Mare Nubium, Rimae on the floor of the crater Gassendi, and Rimae Triesnecker, located between Mare Vaporum and Sinus Medii. Young Crescents Photographing very young, or very old crescents can also be an interesting challenge.
Very thin crescents are difficult to shoot because they are never very far away from the Sun, and the sky is usually quite bright when they are highest above the horizon. The best time to shoot a young crescent after sunset is in the springtime in the northern hemisphere when the ecliptic is most vertical in relation to the horizon after sunset. This will give you the greatest distance between the Moon and the horizon after sunset before the Moon sets. The best time to shoot an old crescent moon before sunrise is in the fall in the northern hemisphere, again when the ecliptic is most vertical in relation to the horizon before sunrise. Thin crescent moons that are low on the horizon are affected by atmospheric extinction and transparency. The best way to determine the correct exposure is by shooting a series of test exposures and examining the results. Lunar Phase Exposure Table The following exposure table will give you a starting point for lunar exposures. It uses the rule of thumb that the correct exposure for the full Moon high in the sky is a shutter speed equal to about 1/ISO at f/11 to f/16. That is, if you are shooting at ISO 200, use a shutter speed of 1/200th second at f/11 to f/16. At ISO 400, use a shutter speed of 1/400th second at f/11 to f/16, and so on. The full Moon is illuminated by direct frontal sunlight. As the phase of the Moon, and the illumination angle changes, you will need more exposure. The correct exposure will grow longer as the Moon goes from full to gibbous to quarter to crescent.
You can easily convert these exposures for different f/stops by remembering that one full f/stop requires a doubling or halving of exposure or ISO. For example, going from f/11 to f/8 is one full stop faster, or larger, in aperture. Since more light is gathered by a larger aperture, you can use a shorter shutter speed, or a lower ISO, by a factor of 2. For example, if you want to shoot the full Moon, the table above calls for an exposure of 1/250th of a second at f/11 at ISO 200. If you are shooting with a telescope that is f/8, it is one stop faster than f/11. So you can shoot at an exposure of 1/500th of a second at ISO 200 at f/8, or you can change the ISO and shoot at 1/250th of a second at f/8 at ISO 100. For high-resolution close-ups of craters where your focal length and magnification are high, the moon will generally fill the frame. In this case, it's easy to start with an exposure indicated by the meter in the camera. Exposures for Earthshine can vary. Try starting at about 1 to 2 seconds at f/4 at ISO 400. Exposures for a Lunar eclipse range from that of a full Moon when the eclipse just starts to a second or more during totality. Some total lunar eclipses can be exceptionally dark if the Moon passes through the central portion of the umbra, the Earth's shadow, and if the Earth's atmosphere is choked with dust from a volcanic eruption. Exposures for a dark eclipse like this can run 10 seconds or more at f/8 at ISO 1600. Bright total eclipse exposures can run about 1 second at f/8 at ISO 1600 during totality. The nice thing about a DSLR is that you can simply take test exposures and examine the results in real time to evaluate what is the best exposure for your equipment setup and the atmospheric conditions. Tips for Lunar Photography Lunar Features Interesting Lunar Craters and Features for Photography
This list highlights just a small portion of the many fascinating things there are to shoot on the Moon. Check out the resources and references below for more information about the Moon. Resources and References
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