Transmission of energy through space without physical connection through varying electric and magnetic fields

Ex. Light

Water wave

Water just moves up and down

Wave travels and can transmit energy

Time between passage of successive crests

The small range of the electromagnetic spectrum that human eyes percieve as light. Radiation outside this range is invisible to human eyes

(Different wavelengths of light)

No limit on wavelengths; different ranges have different names

(Radio waves, infrared, visible light, ultraviolet, X-rays, gamma rays)

Water boils: 212 F; 100 C; 373 K

Water freezes: 32 F; 0 C; 273 K

All thermal motion stops:

-459 F; -273 C; 0 K

Radiation emitted by an object depending only on its temperature

Tells the temperature of an object by being measured

1. Peak wavelength is inversely proportional to temperature (frequency is directly proportional to temperature)

2. Total energy emitted is proportional to fourth power of temperature 

If one is moving toward a source of radiation, the wavelengths seem shorter; if moving away, they seem longer

Can change perceived frequency of radiation

Depends on relative speed of source and observer

If a continuous spectrum passes through a cool gas, atoms of the gas will absorb the same frequencies they emit

Can also be used to identify elements.

1. Luminous solid, liquid, or dense gas produces continuous spectrum

2. Low-density hot has produces emission spectrum

3. Continuous spectrum incident on cool, then gas produces absorption spectrum

Existence of spectral lines required new model of atom, so that only certain amounts of energy could be emitted or absorbed.

Bohr model had certain allowed orbits for electron

Correspond to energy differences between allowed levels

Modern model has electrol cloud rather than orbit

When light shines on metal, electrons can be emitted

Frequency must be higher than minimum, charachteristic of material

Increased frequency: more energetic electrons

Increased intensity: more electrons, same energy

Can only be understood if light behaves like particles

Two ways to decay:

1. Directly to ground state

2. Cascade one orbital at a time

Chemical composition

Temperature

Radial velocity

The Doppler Shift may cause thermal broadening of spectral lines

Rotation will also cause broadening of spectral lines through the Doppler Effect

Hot gas has charachteristic emission spectrum

Spectra can be explained using atomic models, with electrons occupying specific orbitals

Emission and absorption lines result form transitions between orbitals

The bending of a beam of light as it passes from one transparent medium into another. ex. glass

Uses a lens to gather and concentrate a beam of light

Light traveling through lens is refracted differently depending on wavelength

Some light traveling through lens is abosorbed

Large lens can be very heavy, and can only be supported at edge

A lens needs to optically acceptable surfaces, mirror needs only one

Light-gathering power: Improves detail

Brightness proportional to square of radius of mirror

Solutions:

Put telescopes on mountaintops, especially in deserts

Put telescopes in space

Similar to optical reflecting telescopes

Prime focus

Less sensitive to imperfections (due to longer wavelength); can be made very large

Largest: Arecibo

Advantages of radio astronomy:

Can observe 24 hours a day

Clouds, rain, and snow don't interfere

Observations at an entirely different frequency; get totally different information

Combines information from several widely spread radio telescopes as if it came from a single dish

Resolution with be that of dish whose diameter= largest separation between dishes

Involves combining signals from two receivers; teh amount of interference depends on the direction of the signal

Can get radio images whose resolution is close to optical

Can also be done with visible light but is much more difficult due to shorter wavelengths

can produce an image where visible radiation is blocked; generally can use optical telescope mirrors and lenses

these telescopes can also be in space

X rays and gamma rays will not reflect off mirrors as other wavelengths do;

X rays will reflect at a very shallow angle and can therefore be focused

Gamma rays cannot be focused at all; images are therefore coarse

Now known: The solor system has 169 moons, one star, eight planets, eight asteroids, more than 100 Kuiper belt objects, and many smaller asteroids, comets, and meteoroids

More than 800 extrasolar planets have been found

1. Orbital Period

2. Radius

3. Masses

4. Rotation Period

5. Density

1. can be observed

2. known from angular size

3. Newton's laws

4. from observations

5. can be calculated knowing radius and mass

All orbits but Mercury's are close to the same plane

Mercury, Venus, Earth, Mars

Small and rocky

Close to the Sun

rotate slowly

Weak magnetic fields

Few moons

No rings

Jupiter, Saturn, Uranus, Neptune

Large and gaseous

Far from the Sun

Rotate quickly

Strong magnetic fields

Many moons

Rings

All have atmospheres; but they are very different; surface conditions vary as well]

Only Earth has oxygen in its atmosphere and liquid water on its surface

Earth and Mars spin at about the same rate; Mercury is much slower, Venus is slow and retrograde

Only Earth and Mars have moons

Only Earth and Mercury have magnetic fields

Asteroids and meteoroids have rocky composition; asteroids are bigger

Comets are icy with some rocky parts

Pluto, once classified as one of the planets, is the closest large Kuiper belt object to the sun

27 km/s

_______________________= 0.009%

300,000 km/s

20 km/s

__________________=0.007%

300,000 km/s

E=(6.63 x 10^-34) x 3000=

1.989 x 10^-30 J