ELECTROMAGNETIC SPECTRUM SPECTROSCOPY AND DOPPLER WAVE ELECTROMAGNETIC SPECTRUM

Other light characteristics All radiant energy travels through the vacuum of space in a straight line at the rate of 300, 000 kilometers. 1 day = 26 billion kilometers.

Other light characteristics Photon A quantum of visible light. (Quantum – smallest quantity of energy) A photon has neither mass nor electrical charge. A photon possesses energy and momentum. A photon can exert pressure on matter. (Radiation pressure) Responsible for “pushing” material away from a comet to produce its tail.

Comet Hale-Bopp

SPECTROSCOPY Spectroscopy – study of the properties of light that depend on wavelength. Newton’s study on prism initiated this study. Also defined as the study of spectra, especially to determine the chemical composition of substances and the physical properties of molecules, ions and atoms.

SPECTROSCOPY Spectroscope Instrument for studying spectra; an instrument for dispersing light usually light in the visible range, into a spectrum in order to measure it.

SPECTROSCOPY Three types of spectrum: 1. Continuous spectrum 2. Dark-line spectrum (Absorption spectrum) 3. Bright-line spectrum (Emission spectrum)

SPECTROSCOPY 1. Continuous spectrum Is produced by an incandescent solid, liquid or gas under high pressure. Consists of an uninterrupted band of color. E.g. Common light bulb

Spectrum

SPECTROSCOPY 2. Dark-line spectrum (Absorption spectrum) Is produced when “white” light is passed through a comparatively cool gas under low pressure. Gas absorbs selected wave length of light so the spectrum that is produced appears as a continuous spectrum, but with a series of dark lines.

Spectrum

SPECTROSCOPY 3. Bright-line spectrum (Emission spectrum) It is a series of bright lines of particular wavelengths, depending on the gas that produces them. These bright lines appear in the exact location as the dark lines that are produced by this gas in a dark-line spectrum (absorption).

Spectrum

SPECTROSCOPY Most stars have dark line spectra. Each element produces a unique set of spectral lines. Each spectrum acts as a “finger print” of a star and is used to identify the element present.

SPECTROSCOPY Spectrum of a star (sun) explained in an overly simplified manner: Central region – high pressure and high temperature – continuous spectrum. Outer region – low pressure and low temperature – dark-line spectrum. Dark lines in the spectrum are absorbed light.

SPECTROSCOPY The spectrum of the sun contains thousands of dark lines. Over 60 elements have been identified by matching those lines with those of elements known on Earth.

SPECTROSCOPY TWO FACTORS CONCERNING A RADIATING BODY 1. If the temperature of a radiating surface is increased, the total amount of energy emitted is increased. *Stefan Boltzman Law The energy radiated by a body is directly proportional to the fourth power of its absolute temperature. E.g. Star – Temperature doubled – energy emitted times 2 raise to 4 (16 times more energy.)

SPECTROSCOPY TWO FACTORS CONCERNING A RADIATING BODY 2. As the temperature of an object increases, a larger proportion of its energy is radiated at shorter wavelengths. E.g. Heated Metal rod Red – longer wavelength – hot Blue – shorter wavelength – hotter Red stars – hot Blue stars - hotter

DOPPLER EFFECT Doppler effect Explained by Christian Doppler in 1842. change in frequency because of motion: a perceived change in the frequency of a wave as the distance between the source and the observer changes.

DOPPLER EFFECT When a light source is moving away, its light appears redder than it actually is. The reason for it is that the wavelength is stretched. Objects approaching have their wavelength waves shifted toward blue (shorter wavelength).

Sodium lines

DOPPLER EFFECT Case analysis: If a source of light is approached you at a very high speed (near the speed of light), It would appear blue. If you move with a speed of light the color of a stationary light source will appear blue.

DOPPLER EFFECT By using the Doppler effect It reveals weather Earth is approaching or receding from a star or another celestial body. The amount of shift allows to recalculate the rate at which the relative movement is occurring. Larger Doppler shifts indicate higher velocities. It is generally measured in from dark lines in the spectra of stars by comparing them with a standard spectrum produced in the laboratory.

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