Apollo Gnomon is a vital component of the Apollo Lunar Module that was used during the Apollo missions to measure the angle between the lunar horizon and the Sun. It was developed to ensure that the astronauts could accurately track the time, navigate and communicate with the Mission Control Center. The Apollo Gnomon was the brainchild of Jack Kinzler, a NASA engineer who was tasked with developing equipment that could aid the astronauts during their missions.
The design of the Apollo Gnomon was simple yet highly effective. It consisted of a staff that was mounted on a tripod with a circular base. The staff had a series of lines and dots that were used to measure the angle between the lunar horizon and the Sun. The Apollo Gnomon was an essential tool that allowed the astronauts to determine the time of day on the Moon and align their cameras and other equipment with the Sun.
Apollo astronauts used a Gnomon as a photographic tool to indicate local verticals, and it displayed a color chart while they were working on the lunar surface. It was used on the lunar surface by NASA astronauts throughout their photographic and scientific tasks.
A Gnomon is a gimbaled stadia rod installed on a tripod so that the rod was free to aim vertically. When deployed on the Moon’s surface, the shadow cast by the rod indicated sun angle and direction.
The painted scale and the rod length provided a reference for determining the dimensions of nearby objects. Shades of gray on the rod covered in reflectivity from 5% to 35%, plus a color scale, enabled the more accurate determination of rock and soil colors by comparison.
The Importance of Apollo Gnomon
The Apollo Gnomon played a critical role in the success of the Apollo missions. It enabled the astronauts to keep track of time and ensure that they were on schedule. It was also used to align the cameras and other equipment with the Sun, allowing for accurate measurements and high-quality photographs. Without the Apollo Gnomon, the astronauts would have faced significant challenges in navigating and communicating with the Mission Control Center.
The Apollo Gnomon is also a timeless symbol of space exploration. It represents the ingenuity, determination, and courage of the men and women who made the Apollo missions possible. It is a reminder of the incredible achievements of NASA and the importance of continued space exploration.
Lunar Sample Collection Procedures Using Gnomon
When time permitted, samples were photographed before being collected. Those photos document the context in which each Moonsample was found, which assists in interpreting the history of the lunar sample.
They used this three-legged device Gnomon for this purpose. Furthermore, the bar on the left leg calibrates both the color of the sample and the size. And from the direction of the Sun’s shadow, the sample’s orientation on the ground could be determined. The Gnomon configuration was slightly different for each Apollo mission.
History of Gnomon
A Gnomon, pronounced (/ˈnoʊmɒn, ˈnoʊmən/, from Greek γνώμων, gnōmōn. It means literally: “one that knows or examines” is part of a sundial that casts a shadow. The name is used for a variety of purposes in mathematics and other fields.
A decorated stick dating from 2300 BC was excavated at the astronomical site of Taosi and is the oldest Gnomon known in China.
The Gnomon was extensively used in ancient China from the second century BC onward to determine seasons, orientation, and geographical latitude changes. The old Chinese used shadow measurements to create calendars mentioned in several ancient texts.
Credit: NASA.
Gnomon on The Moon, Apollo 16
The Gnomon is a stadia rod mounted on a tripod. It is constructed so that the rod will align itself parallel to the local lunar gravity field, pointing essentially vertically.
The gnomon rod, extending about 13 inches above the gimbal, has 10 painted gray steps ranging in absolute reflectance from 2.4% to 39%.
Each gray band is .79 inches wide, and the rod is .44 inches in diameter. The white band above the gray scales is 4.4 inches wide, and the top .5 inch of the rod is painted black.
The Apollo 16 mission’s Gnomon was photometrically calibrated at the historic Manned Spacecraft Center, Texas, through December 2-3, 1971. The main objective of the photometric calibrations is to allow the measurement of the photometric properties of lunar materials.
Credit: NASA.
Lunar Surface Photographs
Lunar surface photographs, which include the Gnomon, have a vertical reference, a calibrated scale for determining the size of rock fragments, and an indication of camera orientation relative to the solar position.
The gray steps permit the determination of scene luminance relationship to film density, which allows photometric measurements of lunar materials to be extracted from film negatives. The photometric properties of lunar
materials and rock types permit their recognition and delineation for geologic mapping at each landing site and aid in the correlation and extrapolation of geologic data from site to site across the lunar surface.
Method of Measurement When Using a Gnomon
The reflectance from the gray steps on the gnomon rod was measured with a DPPD-Scientific telephotometer model 2000. The Gnomon was illuminated with a collimated xenon light, which closely approximates the solar spectrum in the 400 to 700-nanometer range.
The spectral sensitivity of the photomultiplier tube in the telephotometer also approximates the black-and-white lunar surface film’s spectral sensitivity.
The reflectance from each gray step is measured by scanning across the rod diameter with 6-minute and 20-minute apertures and recording the photomultiplier output with a digital recorder. The 6-minute aperture covers an area of about 2 square mm on the Gnomon.
The Light Source is Adjusted to Simulate Solar Elevation
The gray step reflectance is measured over the photometric geometry variations that will occur during the planned lunar surface photography. The light source is adjusted to simulate solar elevation angles of 11°, 22~ 34°.
The telephotometer is positioned to simulate the camera view angles planned for down-sun and cross-sun photography, which ranges over emission angles (e) of 15°, 20°, and 25° and at azimuth angles of 10° and 80° measured from the sun-line.
The photometric equipment is calibrated before each set of measurements and frequently rechecked during data acquisition. The reflectance measurements are expressed in absolute percentage reflectance based on measurements using a MgO reflectance standard.
A freshly pressed MgO powder plaque is illuminated at an incident angle of 0 degrees, and the reflectance measured at an emission angle of 45° is adjusted to read 100 on the telephotometer.
The Legacy of Apollo Gnomon
The legacy of the Apollo Gnomon lives on today. It has inspired generations of scientists, engineers, and space enthusiasts to continue pushing the boundaries of space exploration. The Apollo Gnomon is also a popular subject of research and study, with many scientists and engineers seeking to understand its design and significance.
In conclusion, Apollo Gnomon is a remarkable achievement in the history of space exploration. It played a crucial role in the success of the Apollo missions and remained an important symbol of human ingenuity and exploration. As we continue to explore the vast reaches of space, we can look to the Apollo Gnomon as a reminder of the incredible achievements that are possible when we push the boundaries of what is possible.
If you’re curious about the inventions from Apollo Program, check out our in-depth analysis of the topic in our article, 42 Inventions from Apollo Program.