Transcript electromagnetic spectrum

24.1 The Study of Light
Electromagnetic Radiation
 Electromagnetic radiation includes gamma
rays, X-rays, ultraviolet light, visible light,
infrared radiation, microwaves, and radio
waves.
 The electromagnetic spectrum is the
arrangement of electromagnetic radiation
according to wavelength.
Electromagnetic Spectrum
Electromagnetic Spectrum
•All electromagnetic radiation travels through space at 300,000
kilometers/second (180,000 miles/second) – the speed of light.
•Notice the human eye can only see a small amount of what
electromagnetic radiation is all around us.
•Analyzing electromagnetic radiation tells us most of what we
know about the universe.
Electromagnetic Spectrum
Electromagnetic Spectrum
Radio waves, microwaves, x-rays, gamma rays, and the spectrum of visible colors are all
really the same thing - electromagnetic energy. The differences are their wavelengths.
Radio waves are long, measuring as much as hundreds of meters between peaks. Gamma
ray wavelengths are extremely short, as little as trillionths of a meter. A photon of shorterwavelength light packs more energy than a photon of longer-wavelength light.
24.1 The Study of Light
The Doppler Effect
 The Doppler effect is the apparent change
in frequency of electromagnetic or sound
waves caused by the relative motions of the
source and the observer.
 In astronomy, the Doppler effect is used to
determine whether a star or other body in
space is moving away from or toward Earth.
The Doppler Effect
Structure of the Sun
24.3 The Sun
The Solar Interior
 Nuclear Fusion
• Nuclear fusion is the way that the sun produces
energy. This reaction converts four hydrogen
nuclei into the nucleus of a helium atom,
releasing a tremendous amount of energy.
• During nuclear fusion, energy is released
because some matter is actually converted to
energy.
• It is thought that a star the size of the sun can
exist in its present stable state for 10 billion
years. As the sun is already 4.5 billion years
old, it is “middle-aged.”
Nuclear Fusion
24.3 The Sun
Structure of the Sun
 Corona
• The corona is the outer, weak layer of the solar
atmosphere.
• The temperature at the top of the corona
exceeds 1 million K.
• Solar wind is a stream of protons and electrons
ejected at high speed from the solar corona.
24.3 The Sun
The Active Sun
 Sunspots
• A sunspot is a dark spot on the sun that is cool
in contrast to the surrounding photosphere.
• Sunspots appear dark because of their
temperature, which is about 1500 K less than
that of the surrounding solar surface.
Sunspots
24.3 The Sun
The Active Sun
 Prominences
• Prominences are huge cloudlike structures
consisting of chromospheric gases.
• Prominences are ionized gases trapped by
magnetic fields that extend from regions of
intense solar activity.
Solar Prominence
24.3 The Sun
The Active Sun
 Solar Flares
• Solar flares are brief outbursts that normally
last about an hour and appear as a sudden
brightening of the region above a sunspot
cluster.
• During their existence, solar flares release
enormous amounts of energy, much of it in the
form of ultraviolet, radio, and X-ray radiation.
• Auroras, the result of solar flares, are bright
displays of ever-changing light caused by solar
radiation interacting with the upper atmosphere
in the region of the poles.
Aurora Borealis
17.2 Heating the Atmosphere
Energy Transfer as Heat
 Heat is the energy transferred from one
object to another because of a difference in
the objects’ temperature.
 Temperature is a measure of the average
kinetic energy of the individual atoms or
molecules in a substance.
17.2 Heating the Atmosphere
Energy Transfer as Heat
 Three mechanisms of energy transfer as
heat are conduction, convection, and
radiation.
 Conduction
• Conduction is the transfer of heat through
matter by molecular activity.
 Convection
• Convection is the transfer of heat by mass
movement or circulation within a substance.
17.2 Heating the Atmosphere
Energy Transfer as Heat
 Radiation
• Radiation is the transfer of energy (heat)
through space by electromagnetic waves that
travel out in all directions.
• Unlike conduction and convection, which need
material to travel through, radiant energy can
travel through the vacuum of space.
Energy Transfer as Heat
17.2 Heating the Atmosphere
Energy Transfer as Heat
 Electromagnetic Waves
• The sun emits light and heat as well as the
ultraviolet rays that cause a suntan. These forms
of energy are only part of a large array of energy
emitted by the sun, called the electromagnetic
spectrum.
Electromagnetic Spectrum
Visible Light Consists
of an Array of Colors
17.2 Heating the Atmosphere
Energy Transfer as Heat
 Radiation
• All objects, at any temperature, emit radiant
energy.
• Hotter objects radiate more total energy per unit
area than colder objects do.
• The hottest radiating bodies produce the shortest
wavelengths of maximum radiation.
• Objects that are good absorbers of radiation are
good emitters as well.
17.2 Heating the Atmosphere
What Happens to Solar Radiation?
 When radiation strikes an object, there
usually are three different results.
1. Some energy is absorbed by the object.
2. Substances such as water and air are
transparent to certain wavelengths of radiation.
3. Some radiation may bounce off the object
without being absorbed or transmitted.
Solar Radiation
17.2 Heating the Atmosphere
What Happens to Solar Radiation?
 Reflection and Scattering
• Reflection occurs when light bounces off an
object. Reflection radiation has the same
intensity as incident radiation.
• Scattering produces a larger number of weaker
rays that travel in different directions.
17.2 Heating the Atmosphere
What Happens to Solar Radiation?
 Absorption
• About 50 percent of the solar energy that strikes
the top of the atmosphere reaches Earth’s
surface and is absorbed.
• The greenhouse effect is the heating of Earth’s
surface and atmosphere from solar radiation
being absorbed and emitted by the atmosphere,
mainly by water vapor and carbon dioxide.
17.3 Temperature Controls
Why Temperatures Vary
 Cloud Cover and Albedo
• Albedo is the fraction of total radiation that is
reflected by any surface.
• Many clouds have a high albedo and therefore
reflect back to space a significant portion of the
sunlight that strikes them.
Clouds Reflect and Absorb Radiation