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