CHAPTER 3: LEARNING GOAL #2 By: Windell James and Landris Baggs Astronomy 4 th Block Mr. Richardson

LEARNING GOAL Describe the major regions of the electromagnetic spectrum and explain how the properties of Earth’s atmosphere affect our ability to make astronomical observations at different wavelengths.

SHORT TERM EXPLANATION Electromagnetic spectrum is a collection of all possible occurrences of electromagnetic radiation The following are regions of the electromagnetic spectrum of increasing energy and they include gamma rays, microwave, visible, X-rays, ultraviolet, radio waves and infrared. The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short- wavelength (high-frequency). Most parts of the electromagnetic spectrum are used in science for spectroscopic and other probing interactions, as ways to study and characterize matter. Generally, electromagnetic radiation is classified by wavelength into radio wave, microwave, terahertz (or sub-millimeter) radiation, infrared, the visible region we perceive as light, ultraviolet, X-rays and gamma rays.

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EXPLANATION OF THE ANSWER Only a small fraction of the radiation produced by astronomical objects actually reaches the surface of the Earth, because of the opacity of our atmosphere. Certain atmospheric gases absorb radiation very efficiently at some wavelengths. Ex. Water vapor(H20)and Oxygen (O2) absorb radio waves having wavelengths less than about a centimeter, while water vapor and carbon dioxide (CO2) are strong absorbers of infrared radiation. Ex. #2. Ultraviolet, X-ray, and gamma radiation are completely blocked by the ozone layer (O3) high in Earth’s atmosphere. Ex. #3. the interaction between the Sun's ultraviolet radiation and the upper atmosphere produces a thin, electrically conducting layer at an altitude of about 100 km. The ionosphere, as this layer is known, reflects long-wavelength radio waves (wavelengths greater than about 10 m) as well as a mirror reflects visible light.

EXPLANATION OF ANSWER CONTINUED…………. The effect of all this blockage is that there are only a few windows, at well- defined locations in the electromagnetic spectrum, where Earth's atmosphere is transparent. In much of the radio and in the visible portions of the spectrum, the opacity is low, so we can study the universe at those wavelengths from ground level. In parts of the infrared range, the atmosphere is partially transparent, so we can make certain infrared observations from the ground. Moving to the tops of mountains, above as much of the atmosphere as possible, improves observations. In the rest of the spectrum, however, the atmosphere is opaque. Ultraviolet, X-ray, and gamma-ray observations can be made only from above the atmosphere, from orbiting satellites.