General Wave Properties, the Electromagnetic Spectrum, and

AstronomyBy

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 high-speed 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 (x-ray 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 tele-communications 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