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, X-rays, and gamma rays All of these are forms of electromagnetic radiation

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

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

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

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

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

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

Characteristics of Gamma radiation: longest wavelength shortest wavelength Characteristics of Gamma radiation: Shortest wavelength (highest energy). Comes from radioactivity or nuclear reactions. Give off harmful radiation. 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 Ultraviolet X-ray 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 X-Girlfriends Rabbits Mate In Very Unusual eXpensive Gardens Randy Men In Vegas Uses X-rays on Girls Raging Martians Invaded Venus Using X-ray Guns