Video Field Trip: Fireball • How did scientists discover the activity of the sun’s core? • How do auroras occur?
The Study of Light Chapter 24, Section 1
Electromagnetic Radiation • Electromagnetic radiation includes gamma rays, X-rays, ultraviolet light, visible light, infrared radiation, microwaves, and radio waves • Electromagnetic Spectrum – the arrangement of electromagnetic radiation according to wavelength • All energy, regardless of wavelength, travels through the vacuum of space at the speed of light (300,000 km/s) • Light has a dual nature, it is both a wave and a particle • Each color of light has a specific wavelength (with red having the longest and violet having the shortest) • Photon – a small packet of light energy • Shorter wavelengths have more energetic photons
Concept Development • What are photons?
Spectroscopy • Spectroscopy – the study of the properties of light that depend on wavelength • Continuous Spectrum – an uninterrupted band of light emitted by an incandescent solid, liquid, or gas under pressure • Absorption Spectrum – a continuous spectrum produced when white light is passed through a cool gas under low pressure; the gas absorbs selected wavelengths of light, and the spectrum looks like it has dark lines superimposed • Emission Spectrum – a series of bright lines of particular wavelengths produced by a hot gas under low pressure • When the spectrum of a star is studied, the spectral lines act as “fingerprints” • These lines identify the elements present and thus the star’s chemical composition
Concept Check • Compare and contrast the three different types of spectra.
The Doppler Effect • Doppler Effect – the apparent change in frequency of electromagnetic or sound waves caused by the relative motions of the source and the observer • The light from a source that is moving away from an observer appears redder than it actually is because its waves are lengthened (red-shift) • This effect is only visible to the human eye when objects are moving close to the speed of light • In astronomy, the Doppler effect is used to determine whether a star or other body in space is moving away from or toward Earth • Large Doppler shifts indicate higher speeds; smaller Doppler shifts indicate slower speeds
Concept Check • How can scientists determine whether a star is moving toward or away from Earth?
Assignment • Read Chapter 24, Section 1 (pg. 674-677) • Do Chapter 24 Assessment #1-34 (pg. 695-696)