Electromagnetic Spectrum

• Different forms of radiation arranged in order according to their wavelength.– Travels through space at 300,000 km/s or 186,000 m/s

• Wavelength – the distance from the crest of one wave to the crest of the next wave.

• Frequency – the number of waves passing at a given point in a second.– High Frequency = short wavelengths– Low Frequency = long wavelengths.

Radio waves• Longest rays• Red color• Naturally made by: lightning, astronomical

objects.• Everyday uses: sound

transmissions/broadcasting, computer systems, navigation systems.

Microwaves

• “micro” used to mean smaller than radio waves.

• Good for transmitting information.• Can penetrate haze, light rain, snow, clouds,

and smoke.• Discovery by accident!– Used to detect the Cosmic Microwave

Background, which showed evidence of the Big Bang.

Infrared• Between Microwaves and Visible light in the

electromagnetic spectrum.• Can be felt in the form of heat– Examples: the Sun, Fire

• Can also be used for things such as your TV remote.• Images can be falsely color in a number of ways so

we can interpret the information.• the Infrared Astronomy Satellite (IRAS) looks into

space and measures infrared light coming from things like large clouds of dust and gas, stars, and galaxies!

Visible Light Waves

• Only part of the Electromagnetic Spectrum we can see.

• Each color has a different wavelength• Red = longest• Violet = Shortest• When the colors are seen together it makes

white light.

Ultraviolet Waves• Between Visible Light and X-rays• UV rays from the Sun is what gives us

sunburns.• Most of these rays gets block by the ozone

layer, but some still get through.• Astronomers can use Ultraviolet wave to

detect different types of stars.• Telescopes used to detect ultraviolet– Hubble Space Telescope, Extreme Ultraviolet

Explorer, International Ultraviolet Explorer

X-Ray waves• Higher energy than ultraviolet.• Acts more like a particle than a wave.• The atmosphere is thick enough that no x-rays

reach the Earth.• Instead we must put telescopes and detectors

of satellites.• Can be used to detect things like black holes,

neutron stars, binary star systems, supernova remnants, stars, the Sun, and even some comets.

Small Magellanic Cloud. The false-colors show what this supernova remnant looks like in X-rays (in blue), visible light (green) and radio (red).

Gamma-ray Waves• Shortest wavelength• Most energy• Generated by radioactive atoms and nuclear explosions.• Can kill living cells (like cancer in medicine!)• Does not reach the surface of Earth, only the upper

atmosphere.• Supernova explosions, neutron stars and pulsars, and black

holes are all sources of celestial gamma-rays.• Uses a particle called photons to capture Gamma-rays.• Gamma-ray bursts can release more energy in 10 seconds

than the Sun will emit in its entire 10 billion-year lifetime! • So far, it appears that all of the bursts we have observed

have come from outside the Milky Way Galaxy.

Spectroscope

• Used by astronomers to study spectrums of distant stars

• Use a prism to split light into a spectrum of colors.

Continuous Spectrum

• Unbroken band of colors• Light is sent out in all visible wavelengths

(colors)• Known as Continuous Spectra• Emitted by glowing solids, liquids and hot

compressed gases in stars.

Emission Spectrum

• Uneven spaced series of lines with different colors and brightness

• Colored lines on a black background.• Known as bright-line spectrum

Absorption Spectrum• A continuous spectrum crossed by dark lines.• Dark lines due to light passing through a cooler

gas• Dark line position helps you identify the element• Used to study the star’s outer layer and the

composition of a planet’s atmosphere• Known a dark-line spectrum

Using Spectra to detect Doppler Effect