Transcript the ELECTROMAGNETIC SPECTRUM / WAVE PROPERTIES

General Wave Properties, the
Electromagnetic Spectrum, and
Astronomy
By
Leslie McGourty and Ken Rideout
(modified by your teacher)
All the information on waves that’s fit to print
What is a wave?
• A wave is a transfer of energy from one
point to another via a traveling disturbance
• A wave is characterized by its wavelength,
frequency, and amplitude
• There are 2 main types of waves:
longitudinal (like sound) and
TRANSVERSE (like electromagnetic
waves)
Why do we care about waves?
• Because the best way to learn about
astronomical objects such as STARS,
GALAXIES, AND BLACK HOLES that
are MANY TRILLIONS OF MILES
AWAY is to study the
ELECTROMAGNETIC ENERGY
WAVES THAT THEY EMIT
(give
off)
Transverse Waves
Waves that travel perpendicular to the direction of motion
Examples: Ocean waves, all forms of electromagnetic
energy
Wavelength
• Distance from one crest to the next crest
(or trough to trough)
• Measured in meters
Frequency
• Number of crests passing by a given point per second
• Measured in Hertz (Hz) defined to be one cycle per sec
• Equal to the inverse of the amount of time it takes one
wavelength to pass by
WAVELENGTH AND FREQUENCY
ARE
INVERSELY RELATED:
FREQUENCY AND ENERGY ARE
DIRECTLY RELATED:
WAVELENGTH AND ENERGY
ARE
INVERSELY RELATED:
Electromagnetic Waves
• Waves of energy that have both electrical and magnetic
properties
• Any object that is above absolute zero emits
electromagnetic waves
• The entire group of waves with these properties is called
the “Electromagnetic Spectrum”
• Still confused? Then click What are electromagnetic
waves?
• To move onto the EM spectrum click
The Electromagnetic
Spectrum
• Think you know all about the
electromagnetic spectrum? Well
take a tour of the Electromagnetic
Spectrum to find out more cool
information.
• The Following slides show and
explain the different types of
Electromagnetic Radiation
TYPES OF ELECTROMAGNETIC WAVES
GAMMA RAYS
• Emitted from the nuclei of
atoms during radioactive
decay or during highspeed collisions with
particles.
• Sources: Black holes,
stars, supernovae
• Used in cancer treatment
and for sterilization
Sources: Cobalt 60, the
inner core of the sun
• Gamma ray image of The
center of the Milky Way
(where a black hole
resides)
X-RAYS
• Emitted when an
electron that is moving
very quickly is suddenly
stopped , or
• emitted by heavy atoms
after bombardment by
an electron
• Used for radiography (xray photography) and to
look at materials in
industry for defects
X RAY ASTRONOMY
• X ray image of the night sky (can you spot
the disk of the Milky Way?)
ULTRAVIOLET RAYS
• Above the color violet
• Three groups - UV A, UV B, and
UV C.
• “A” type: longest wavelength;
least harmful
• UV B and UV C are absorbed
by DNA in cells
• Used by the body to produce
vitamin D, to kill bacteria on
objects, and for sun tanning
• Sources: Ultra hot objects
5000°C or more, such as Stars
ULTRAVIOLET ASTRONOMY
• Ultraviolet energy
emitted by the sun
• Ultraviolet image
of a distant
galaxy
VISIBLE LIGHT
• White light:
combination of all the
colors
• Rainbow: white light that
has been separated into
a continuous spectrum of
colors
• Used for communications
(fiber optics)
• Sources: very hot
objects (stars,
galaxies)
• Galaxies emit enough
visible light to be seen
from great distances
VISIBLE LIGHT PROPERTIES
VISIBLE LIGHT another view:
VISIBLE LIGHT ASTRONOMY
• The Eagle
Nebula: a
massive Star
forming
“cloud” within
the Milky Way
• Each
“column” of
dense
gas/dust is
many Trillions
of miles tall
INFRARED
• “Below” Red visible
light
• Thought of as heat but
is not always
• Far infrared energy is
heat energy.
• All objects that have
warmth radiate
infrared waves
• Easily absorbed and
re-radiated.
• Used in remote
controls, surveillance,
therapy of muscles
• Sources: Humans,
most astronomical
objects
INFRARED ASTRONOMY
• Nebulae, like the
Orion nebula, emit
Infrared energy
• Infrared image of the
nucleus and coma of
comet Hale-Bopp
MICROWAVES
• 1 mm-1 dm in
length
• Absorbed by
water molecules –
how microwave
ovens heat food
• Used in telecommunications
and power
transmission
• Sources: electric
circuits,
microwave ovens,
stars
• The microwave image below
(from COBE) helped to prove
the Big Bang Theory
MICROWAVE ASTRONOMY
• This is a
microwave
image of
the ENTIRE
UNIVERSE
(from WMAP)
RADIO WAVES
• 10 cm- 100,000+m in length
• Only cosmic waves the reach
the surface of the Earth
• Cause of noise
• Divided into smaller frequency
dependent groups called
bands
• Used for communications,
gadgets- cell phones,
microwaves, remote controls,
garage door openers
• Sources: transmitters and
sparks from motors, stars,
black holes
• Science- radio astronomy,
atmospheric research
RADIO
ASTRONOMY
• Radio-synthesized
image of the Crab
Nebula
• The V.L.A. radio
telescope array in New
Mexico
Composite
astronomy
• A complete
picture of this
Supernova
remnant is
created by
combining
images from the
different types of
electro-magnetic
energy emitted
•
•
•
•
HOW TO IDENTIFY THE COMPOSITION
OF OBJECTS
Hydrogen
Helium
Carbon
Iron
When heated, each element emits its own unique and distinct pattern of
wavelengths of light. This is known as a SPECTRAL FINGERPRINT.
By using a database of these “fingerprints”, astronomers can identify the
composition of a distant object.
For example, the spectral pattern produced by a star is shown below.
It matches the spectral fingerprint of Hydrogen – therefore, we now know that
the star is composed of Hydrogen gas!
• The 3 types of spectra:
– Coninuous: “solid rainbow” –
solids and ionized gases
(random electrons)
– Absorption: when white light
passes through a cool gas –
black lines appear in spectrum –
show “missing” lines – absorbed
by gas – shows gas’ identity
– Emission: by heated gases
(fingerprints)
How light is used to determine the
movement of stars/galaxies
How light is used to detect “invisible”
alien planets:
By measuring the cyclical Doppler shift of a star, astronomers can
figure out how far the star is wobbling, which allows them to figure
out THE MASS OF ITS ORBITING PLANET, AND ITS DISTANCE
FROM THE STAR