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

Electromagnetic Spectrum

Spectrum of Light

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

Three Types of Spectra

Solar Spectrum

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

The Doppler Effect

Measurement of Doppler Shifts

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)