You might think there are places in the sky where it would be almost totally dark, but there’s always a glow from ambient light. Besides, most EM radiation is invisible to us, so even light that is very “bright” in one area of the EM spectrum could be completely “dark” in the visible part of the spectrum.
The cumulative effects of direct and reflected starlight create a light bath that affects even the back side of the Moon. NASA’s LAMP (Lyman-Alpha Mapping Project) sensor is designed to observe and analyze the light reflecting from the Moon - specifically in the ultraviolet energy band of the electromagnetic spectrum. Ultraviolet light has energy just higher than our eyes can see; “ultra” means “beyond.” Ultraviolet waves are between visible light and x-rays on the spectrum. In fact, the reflected light LAMP is studying includes many more bands besides ultraviolet, but the NASA team is interested in the Moon’s ultraviolet profile, partly because it hasn’t yet actively been studied in ultraviolet yet.
Each band of the EM spectrum is actually a continuum itself, and the LAMP team intends to break the ultraviolet band into its component parts – much the same way you might break white light into its component colors: red, orange, yellow, green, blue, indigo, and violet. By slicing the ultraviolet zone into smaller bands using a spectrograph, scientists can get a more precise picture of the Moon’s ultraviolet profile. The results will offer new information about what the Moon is made of.
Hydrogen atoms in water molecules emit – or absorb, depending on whether electrons are gaining or losing energy – light that corresponds to ultraviolet wavelengths LAMP can sense. As LAMP images the moon, it maps areas where there could be water – ice frozen under the polar caps, for example. Because the moon doesn’t tilt very much on its axis, deep craters at the poles could have been in shadow for billions of years, creating cold conditions that could trap hydrogen and possibly ice. The LCROSS impact in 2009 confirmed that ice lies in these craters. See http://lcross.arc.nasa.gov/observation.htm. Scientists believe water from passing comets or embedded hydrogen in the moon’s composition could coalesce over time into ice deposits. There’s already some evidence of hydrogen markers, which scientists in the video refer to as the “Lyman alpha glow.” LAMP will further refine our understanding of where the hydrogen might be and whether indeed there could be ice deposits. Lunar water could be used to support future human presence on the moon. Also, water can be broken down into its component molecules and used to produce rocket fuel.
Here on Earth, the ultraviolet light we receive comes primarily from the Sun. In fact, it’s ultraviolet rays that cause our skin to tan and burn when we’re outside on a sunny day. (That’s why sunscreen is formulated specifically to block UV rays.) Many animals make use of ultraviolet light: bees, spiders, some birds, and other animals can see ultraviolet light. A “black light” emits mostly ultraviolet light, with some “near” ultraviolet light that’s close to the visible band.
Randy Gladstone: In the night sky, there's a...a sort of a glow throughout the sky that is shining down on even the night side of the Moon. You get diffuse lighting from all around the sky, and we're looking at the reflection from that source of light. LAMP stands for Lyman-Alpha Mapping Project. It's an experiment that looks in the ultraviolet --at the reflected light from the Moon's surface to determine composition and whether frost is there.
Kurt Retherford: So LAMP is neat because we're gonna look at the lunar nightside as well as the lunar dayside. We're sensitive enough to look at reflected starlight from the surface of the Moon, and also the specific wavelength from hydrogen atoms that are sort of shining throughout the solar system.
Dana Hurley: A spectrograph is a type of instrument that breaks up light into its rainbow, so what LAMP does is it breaks up the ultraviolet part of the rainbow up into the different ultraviolet colors--and it's telling us about what the Moon is made out of. So LAMP is going to see some things that we haven't seen before because we haven't extensively studied this part of the spectrum on the Moon. Randy Gladstone: LAMP is able to see in the dark because because at ultraviolet wavelengths--which are more energetic photons than we look at with our eyes--there's this Lyman-Alpha glow that shines on it from all over the place.
Kurt Retherford: An instrument quite like ours has never been to the Moon, and it's a new generation of instruments and we're gonna do a bang-up job of measuring the ultraviolet light coming from the Moon.
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