The Moon is the one (and only) natural satellite of Earth It orbits Earth approximately every 29.5 days at a distance of about 385,000 kilometers (or 1.28 light seconds!). The lunar diameter of 3476 km is about 1/4 that of Earth, but it's mass is only one percent of our home planet's mass. Apart from Earth, the Moon is the only body in our Solar System to exhibit human footprints. The first of six manned missions by NASA astronauts landed on the Moon in July 1969 in what ranks as one of the greatest accomplishments in human history.
To learn more about the Moon, click on the title label at the top of this page.
Visible: Galileo and Visible: TIE - Colleen Gino
The above images were obtained during a full moon phase, where Earth lies between the Sun and the Moon. If all three bodies were to lie in the same orbital plane, we would see a lunar eclipse, in which the Moon moves through Earth's shadow for a few hours. In the case where a new moon is situated between the Sun and Earth in the same orbital plane, it is possible to experience a total solar eclipse of a few minutes duration.
The Moon shines by the reflection of sunlight, and the various gray shades across the lunar disk reveal variations in reflectivity. The darker and flatter regions correspond to large craters and lunar mare (Latin for seas), areas where less sunlight is reflected. The brighter regions are more rugged, and correspond to lunar highlands and mountains, areas with lower solar reflectivity.
This near-infrared view (above) of the Moon was obtained with the Near-Infrared Mapping Spectrometer instrument aboard the Galileo spacecraft in 1992. In this image, taken at a wavelength of 1 micron (1000 nm), just beyond the red portion of the visible-light spectrum. In this false-color photograph, regions of low reflectivity are coded as blue and the high-reflectivity mountains appear as yellow. The red is an artifact of data processing, created by numerical modeling that becomes increasingly unreliable when approaching the terminator or the limb of the Moon.
The mid-infrared image (above) of the Moon was taken during a 1996 lunar eclipse by the SPIRIT-III instrument aboard the orbiting Midcourse Space Midcourse Space Experiment (MSX) satellite. This mission was primarily devoted to monitoring activities funded by the US Department of Defense, but also spent about ten percent of its time looking upwards and obtaining astronomical data! At these wavelengths, MSX was able to characterize the thermal (heat) distribution of the lunar surface during the eclipse. The brightest regions are the warmest, and the darkest areas are the coolest.
In this amazing image, the well-known crater Tycho is the bright object to the south of center. Numerous other craters are also seen as bright spots, indicating that their temperature is higher than in the surrounding dark mare. The Moon is geologically inactive for the most part, and any temperature differences are a result primarily of variations in solar heating (rather than volcanoes, for example). The Moon lacks any appreciable atmosphere to moderate temperatures, which can vary from 130 degrees Celsius in the sun to -110 degrees in the shade.
Radio: NRAO VLA
The brightly-colored radio image of the Moon was made using the National Radio Astronomy Observatory 140-foot diameter telescope in Green Bank, West Virginia. This telescope was taken out of routine astronomical service in 1999. The red regions have the brightest radio emission and represent the warmer areas of the moon. The blue regions have the faintest radio emission. When this image was obtained, the illuminating Sun was clearly to the east (left). You may be interested to know that some astronomers are exploring the possibility of constructing a low-frequency (long-wavelength) radio telescope on the far side of the Moon!
Why? The pressure to fully utilize the radio portion of the electromagnetic spectrum for a wide variety of human communications is causing increased levels of radio interference. The weak celestial signals collected and studied by astronomers are being swamped by stronger man-made emission sources. Despite international protection of certain frequencies for science, some visionary astronomers want to locate a radio observatory on the far side of the Moon. Because this side is perpetually turned away from Earth, it would be protected from the noisy environment that is our home planet.
Turning our attention back to shorter wavelengths, we now examine the ultraviolet view of the Moon (above), courtesy of the Ultraviolet Imaging Telescope aboard the Shuttle-borne Astro-2 payload. This photograph was taken with a camera sensitive to wavelengths ranging from 120 nm to 320 nm. The general appearance of the lunar surface in the UV regime is similar to the visible-light pictures studied earlier, albeit with lower spatial resolution
The very short wavelength x-ray image shows the Moon but barely! Celestial x-rays are normally associated with energetic (and even explosive!) phenomena Given the sedate nature of the Moon, we should not be surprised to see that it is very faint at x-ray wavelengths. If not for the fact that our lunar companion orbits so close to earth, we would be unable to detect x-rays from the Moon. Note that the weak x-rays originate primarily from the bright, Sun-lit side. A careful analysis by astronomers has revealed that the x-ray light from the dark side is only 1 percent of that from the bright side. The mottled (speckle) appearance throughout the image is the result of instrument-induced noise, the astronomical equivalent to static on a portable radio.