Electromagnetic Spectrum Warmup How would you define light

Electromagnetic Spectrum

Warm-up How would you define light?

Light and the Electromagnetic Spectrum • Almost all of our information on space is derived from the light we see • We have only returned samples from the Moon and a comet – Also obtained meteor samples • We have landed (with unmanned probes) on only a handful of planets and moons

Light and the EM Spectrum • The terms light, radiation, and electromagnetic wave can all be used to explain the same concept, they are synonymous • Light comes in many forms and it took physicists some time to realize that x-rays, visible light, radio waves, etc. are all the same phenomena • By using these different tools, astronomers are able to gain a lot of information on various objects Jupiter seen at different wavelengths of light

Light as a Wave • One way to think about light is as a traveling wave • A wave is just a disturbance in some medium (water, air, space) • A wave travels through a medium but does not transport material • A wave can carry both energy and information

Wave Terminology • Wavelength - distance between two like points on the wave • Amplitude - the height of the wave compared to undisturbed state • Period - the amount of time required for one wavelength to pass • Frequency - the number of waves passing in a given amount of time

Wavelengths of Light - Visible • What we see as white light is actually made up of a continuum of components • Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV) • There is actually a continuous transition of color, each with its own wavelength and frequency

The Electromagnetic Spectrum • Human eyes are only able to process information from the visible part of the spectrum • Toward longer wavelengths, the spectrum includes infrared light, microwaves, and radio • Toward shorter wavelengths, the spectrum includes ultraviolet light, Xrays, and gamma rays • All of these are forms of electromagnetic radiation

longest wavelength shortest wavelength Characteristics of Radio waves: 1. Longest wavelength. 2. Transmit radio and TV signals.

longest wavelength shortest wavelength Characteristics of Microwaves: 1. Shorter than radio waves. 2. Absorbed by water molecules.

longest wavelength shortest wavelength Characteristics of Infrared waves: 1. Shorter wavelength than microwaves. 2. Felt as heat. 3. Hot objects give off infrared waves.

longest wavelength shortest wavelength Characteristics of Visible light: 1. Shorter wavelength than infrared waves. 2. Can be seen as colors. 3. Half of Sun’s rays are visible light.

longest wavelength shortest wavelength Characteristics of Ultraviolet light: 1. Shorter wavelength than visible light. 2. Give off harmful radiation. 3. Can kill living cells. 4. Causes skin cancer.

longest wavelength shortest wavelength Characteristics of X-ray radiation: 1. Shorter wavelength than ultraviolet. 2. Give off harmful radiation. 3. Pass through skin, not bone. 4. Harmful to humans.

longest wavelength shortest wavelength Characteristics of Gamma radiation: 1. Shortest wavelength (highest energy). 2. Comes from radioactivity or nuclear reactions. 3. Give off harmful radiation. 4. Harmful to humans.

Warm-up • Complete the worksheet you picked up on the way in (both sides)

EM Spectrum in Astronomy • If we could only observe in visible light, our knowledge of the universe would be greatly limited • By looking at objects at different wavelengths, we get a different view and lots more information • Some objects are only visible at certain wavelengths

The Sun at Different Wavelengths Visible X-ray Ultraviolet X-ray

Measuring Temperature from Light • Astronomers can use the light from an object to measure its temperature • Astronomers also use a different unit for temperature, the Kelvin • Water boils at 373 K and freezes at 273 K – Most stars have a temperature in the 1000's of Kelvin • The coldest possible temperature (absolute zero) corresponds to 0 Kelvin

Measuring Movement from Light • The motion of an object can be measured through a change in the frequency of the waves emitted by the object called the Doppler effect • The increase in pitch of an approaching police car is caused by the compression of the sound wave – The pitch decreases as the police car moves away

Doppler Shift • In astronomy, the same effect happens to light waves • A source that is moving away will appear redder (redshift) • A source that is moving toward us will appear bluer (blueshift) • Note: Only objects moving toward or away from us will show this effect

Mnemonic device • Rotten Men Inevitably Visit Ugly XGirlfriends • Rabbits Mate In Very Unusual e. Xpensive Gardens • Randy Men In Vegas Uses X-rays on Girls • Raging Martians Invaded Venus Using Xray Guns