Light at shorter wavelengths-blue and violet-is scattered by nitrogen and oxygen as it passes through the atmosphere. The sky appears blue because of this scattering behavior. The amount of scattering that takes place depends on the wavelength of the light and the size and structure of the object. Scattering occurs when light bounces off an object in a variety of directions. The graph below from the SPIRE infrared spectrometer onboard the ESA (European Space Agency) Herschel space telescope reveals strong emission lines from carbon monoxide (CO), atomic carbon, and ionized nitrogen in Galaxy M82. Patterns in a spectral signature help scientists identify the physical condition and composition of stellar and interstellar matter. A graph of these data is called a spectral signature. Faint peaks of energy at specific wavelengths can then be detected and recorded. In the case of visible light, the separation of wavelengths through diffraction results in a rainbow.Ī spectrometer uses diffraction (and the subsequent interference) of light from slits or gratings to separate wavelengths. An instrument called a spectrometer uses diffraction to separate light into a range of wavelengths-a spectrum. It is most pronounced when a light wave strikes an object with a size comparable to its own wavelength. Sometimes this warming of air above cities can influence weather, which is called the "urban heat island" effect.ĭiffraction is the bending and spreading of waves around an obstacle. The Landsat 7 satellite image below shows the city of Atlanta as an island of heat compared to the surrounding area. Thermal radiation from the energy-absorbing asphalt and roofs in a city can raise its surface temperature by as much as 10° Celsius. This thermal energy then radiates in the form of longer wavelength infrared energy. Photons bounce around during this absorption process and lose bits of energy to numerous molecules along the way. Thus, the black pavement is hotter than the sidewalk on a hot summer day. For example, black pavement absorbs most visible and UV energy and reflects very little, while a light-colored concrete sidewalk reflects more energy than it absorbs. Some objects, such as darker colored objects, absorb more incident light energy than others. This heat is then emitted from the object as thermal energy. The more an object's molecules move and vibrate, the hotter it becomes. In this image of the Moon's southern hemisphere, low elevations are shown as purple and blue, and high elevations are shown in red and brown.Ībsorption occurs when photons from incident light hit atoms and molecules and cause them to vibrate. A shorter response time means the surface is closer or higher in elevation. The longer the response time, the farther away the surface and lower the elevation. The instrument measures the time it takes a laser pulse to hit the surface and return. This reflective behavior of light is used by lasers onboard NASA's Lunar Reconnaissance Orbiter to map the surface of the Moon.
The physical and chemical composition of matter determines which wavelength (or color) is reflected. Color, in this case, refers to the different wavelengths of light in the visible light spectrum perceived by our eyes. The color of an object is actually the wavelengths of the light reflected while all other wavelengths are absorbed. Very smooth surfaces such as mirrors reflect almost all incident light. Reflection is when incident light (incoming light) hits an object and bounces off.
0 kommentar(er)
