Light as an Electromagnetic Wave

Waves of Oscillating Electric and Magnetic Fields

Wavelength

(λ)

Frequency

(f), in Hz (= waves per second)

Speed

(c) ≈ 300,000 km/s

λ × f

= c

The Electromagnetic Spectrum

Gamma Rays,

X-Rays,

Ultraviolet Light,

Visible Light,

Infrared Radiation,

Microwaves,

Radio Waves

Gamma Rays

(Shortest λ)

Visible Light

λ = 400 – 700 nm

Microwaves

λ > 1 mm

Radio Waves

λ > 10 cm

Gamma rays destroy

biological cells; absorbed in the atmosphere; X-ray satellites see highest energy events

X-rays penetrate

skin and soft tissues; absorbed in the atmosphere; X-ray satellites see superheated gases

UV alters and damages

biological cells; mostly absorbed in the atmosphere; UV satellites: best view of hot stars

Visible light is detected

by the human eye; mostly penetrates the atmosphere; Stars like the Sun peak in the visible

Infrared is detected as

heat; Mostly absorbed in the atmosphere; IR satellites: best view of cool stars, etc.

Radio waves detected by

various electronics; Penetrates the atmosphere; Best view of cold interstellar clouds

The Doppler Effect

Relative motion affects the observed wavelength or frequency of an object

(The Doppler Effect) If distance is decreasing

it’s a blueshift

(The Doppler Effect) If distance increasing

a redshift

Size of shift proportional

to speed