NATS1311 From the Cosmos to Earth Properties of Waves Period: time to complete one cycle of...

NATS1311 From the Cosmos to Earth

Properties of Waves

Period: time to complete one cycle of vibration (From 1 to 5)

Frequency (f): number of crests passing a fixed pointper second

Frequency= 1/period

Example:Period = 1/100 = 0.01 sec. Frequency = 100 hertz (cycles/sec.)


Amplitude (a): maximum displacement fromEquilibrium

Wave length (l): distance between successive crests(2 to 6, 4 to 8, etc...)

Speed (of a wave) (s)= wave length x frequencys= l x f


TYPES OF WAVES

Transverse:Vibration or oscillation is perpendicular to direction

of propagation of wave.

Examples: water wave, vibrating string

Longitudinal:Vibration or oscillation is in the same direction as

propagation of wave.

Examples: sound waves, mass on a spring,loudspeaker


ELECTROMAGNETIC WAVES (LIGHT WAVES)

Velocity 186,000 miles/second

300,000 kilometers/second

3 x 1010 cm/second

• It takes 1 1/3 second for light to travel from the earth

to the moon.

• It takes 8 1/3 minutes for light to travel from the sun

to the earth.


ELECTROMAGNETIC WAVES (LIGHT WAVES)

Speed of propagation of a light wave:

c = l x f

c = velocity of light; c is a constant in vacuum

l = wavelength of a light wave - distance between

successive crests

f = frequency of a light wave - number of crests

passing a fixed point in 1 second


PHOTON•Light propagates as quanta of energy called photons•Photons •move with speed of light•have no mass•are electrically neutral

• Energy of a photon or electromagnetic wave:E = hf = h c/ l

whereh = Planck’s constantf = frequency of a light wave - number of

crests passing a fixed point in 1 secondc = velocity of lightl = wavelength of a light wave -

distance between successive crests

NATS1311 From the Cosmos to Earth FIG. 6.4

Figure 6.4 The electromagnetic spectrum. The unit of frequency, hertz, is equivalent to waves per second. For example, 103 Hz means that 103 wave peaks pass by a point each second.


Absorption and Emission. When electrons jump from a low energy shell to a high energy shell, they absorb energy. When electrons jump from a high energy shell to a low energy shell, they emit energy. This energy is either absorbed or emitted at very specific wavelengths, which are different for each atom.

When the electron is in a high energy shell,t he atom is in an excited state.

When the electron is in the lowest energy shell, the atom is in the ground state.


The Hydrogen Atom. The hydrogen atom is the simplest of atoms. Its nucleus contains only one proton which is orbited by only one electron. In going from one allowed orbit to another, the electron absorbs or emits light (photons) at very specific wavelengths.

NATS 1311 From the Cosmos to Earth Fig.6.6

Figure 6.6 (a) Photons emitted by various energy level transitions in hydrogen. (b) The visible emission line spectrum from heated hydrogen gas. These lines come from transitions in which electrons fall from higher energy levels to level 2. (c) If we pass white light through a cloud of cool hydrogen gas, we get this absorption line spectrum. These lines come from transitions in which electrons jump from energy level 2 to higher levels.

NATS 1311 From the Cosmos to Earth

Kirchhoff’s Laws of Radiation

First Law. A luminous solid, liquid or gas, such as a light bulb filament, emits light of all wavelengths thus producing a continuous spectrum of thermal radiation.

Second Law. If thermal radiation passes through a thin gas that is cooler than the thermal emitter, dark absorption lines are superimposed on the continuous spectrum. The gas absorbs certain wavelengths. This is called an absorption spectrum or dark line spectrum.

Third Law. Viewed against a cold, dark background, the same gas produces an emission line spectrum. It emits light of discrete wavelengths. This is called an emission spectrum or bright line spectrum. .

NATS 1311 From the Cosmos to Earth Fig.6.11

Fig. 6.11 This diagram illustrates Kirchhoff’s laws of radiation.


Figure 6.19 The basic design of a spectrograph.

NATS 1311 From the Cosmos to Earth Fig. 6.7

Figure 6.7 Emission line spectra for helium, sodium, and neon. The patterns and wavelengths of lines are different for each element, giving each a unique spectral fingerprint.


Figure 6.13 The Doppler effect. (a) Each circle represents the crests of sound waves going in all directions from the train whistle. The circles represent wave crests coming from the train at different times, say, 1/10 second apart. (b) If the train is moving, each set of waves comes from a different location. Thus, the waves appear bunched up in the direction of motion and stretched out in the opposite direction. (c) We get the same basic effect from a moving light source.


Figure 6.14 Spectral lines provide the crucial reference points for measuring Doppler shifts.


Lenses and Mirrors

Object distance: do distance from lens or mirror to object.

Image distance: di distance from lens or mirror to image

Focal length: Distance from lens or mirror to image when

the object is at infinity (a long distance away).

Lens formula:

€

1f

=1do

+1di


Lens and Mirror AberrationsSPHERICAL (lens and mirror)

Light passing through different parts of a lens or reflected from different parts of a mirror comes to focus at different distances from the lens.

Result: fuzzy image

CHROMATIC (lens only)

Objective lens acts like a prism.

Light of different wavelengths (colors) comes to focus at different distances from the lens.

Result: fuzzy image


Figure 6.15 (a)The basic design of a refracting telescope. (b) The 1-meter refractor at the University of Chicago's Yerkes Observatory is the world's largest refracting telescope.


Figure 6.17 Alternative designs for reflecting telescopes.


Figure 6.20 Observatories on the summit of Mauna Kea in Hawaii. The twin domes near the far right house the two Keck telescopes.


Figure 6.25 The Arecibo radio telescope in Puerto Rico is the world's largest single radio dish.


Figure 6.21 This diagram shows the basic components of the Hubble Space Telescope, which orbits the Earth. The entire observatory is roughly the size of a school bus.

NATS 1311-From the Cosmos to Earth

Solar System

% Mass of Solar System

Sun 99.85%

Jupiter 00.10%

Others 00.05%

Terrestrial Planets:

•Mercury, Venus, Earth, Mars

– Rocky, Silicates, Metals

Jovian Planets:

•Jupiter, Saturn, Uranus, Neptune, Pluto (icy moon)

– Gases, Liquids

NATS 1311-From the Cosmos to Earth

Solar System

Figure 7.1 Side view of the solar system. Arrows indicate the orientation of the rotation axes of the planets and their orbital motion. (Planetary tilts in this diagram are aligned in the same plane for easier comparison. Planets not to scale.) Seen from above, all orbits except those of Mercury and Pluto are nearly circular. Most moons orbit in the same direction as the planets orbit and rotate--counterclockwise when seen from above Earth's North Pole.


Full moon


Moon

Distance from earth: 238,000 milesDiameter: 2100 miles (1/4 earth)Mass moon/mass earth: 0.012Density: 3.34 gm/cm3

Gravity: 1/6 that of earth


MoonAppearance:

Highlands - heavily cratered

Maria- smoother

Mountain ranges

Rilles - clefts in surface

Craters

Diameter 200 miles to 1 millimeter

Rims higher than grand canyon

Rotation - phase locked to earth

Synodic period - 29 1/2 days

Sidereal period - 27 1/3 days

Surface - igneous rocks - cooled lava

Apollo 17Lunar Mass Spectrometer on surface of moon.

Close-up of mass spectrometer on lunar surface.

Apollo 17 mass spectrometer found principal gases in atmosphere to be hydrogen, neon and argon.


South pole of moon


South pole craters


Silver spur


Lunar rover


Earthrise as seen from the moon


Apollo lunar exploration results

1. Surface composition

Earth - like rocks but not exactly

Basalt - rapidly cooled lava - abundant on

Earth

Anorthosite- more slowly cooled lava- found

Principally in adirondac mountains

Breccias - mixture of fragments of other types of rocks

Kreep - potassium, rare earth, phosphorus

Rocks found in highlands mounts

Soils - contain tiny glass beads - elements with

High melting points

No water

Regolith - ground up rock


2. Chronology

Moon formed 4.6 billion years (by) ago

Oldest rocks - 4.4 by

Youngest rocks - 3.1 by

Volcanism from 3.8 to 3.1 by ago -

internal heating

Moon dead for last 3.1 by

3. Interior

Core - probably molten metal

Mantle - silicate materials

Crust

40 mile thick on near side

80 mile thick on far side

Mascons - regions of high gravity under the maria


4. Origin - 4 theores, first three have problems listed below each theory

1. Fission - moon split off from earth chemical dissimilar - low iron in moon angular momentum

2. Capture - came from elsewhere in solar system orbital mechanics chemical similarities - low iron in moon

3. Double planet - both formed locally chemical differences angular momentum


4. Giant lmpact - Body 10% size of earth impacted

young earth at a grazing angle. Melted but threw off layer of material that condensed into moon. ~ Most likely theory.

5. AtmosphereVery rarifiedPressure: one 100th of one trillionth of earth

(10-14 of earth)A very good vacuum

Composition: mostly noble gases


Figure 7.9 Artist's conception of the impact of a Mars-size object with Earth, as may have occurred soon after Earth's formation. The ejected material comes mostly from the outer rocky layers and accretes to form the Moon, which is poor in metal.


Mercury

Property Earth Mercury

Equatorial Diameter 1 0.4

Density (gm/cm3) 5.5 5.4

Avg. Distance from Sun (AU) 1 0.4

Orbital Period (days) 365 88

Sidereal Rotation Period (days) 1 59

Inclination of axis to orbital plane 23.5° 7°

Inclination of orbit to ecliptic plane 0° 7°

Maximum angle from sun ~ 28°

Surface temperature ~ Day: 800°F

~ Night: -280°F

Atmosphere - pressure 1 atmosphere 10-15 atmosphere

Atmosphere - composition N2, O2 Helium, sodium, potassium, oxygen


The orbit of Mercury

At an average distance of only 58 million kilometers (36 million miles) from the sun, mercury takes a mere 88 days to go around its orbit.

As viewed from earth, mercury can be seen only near times of greatest eastern or western elongation.

At greatest western elongation (when the planet is farthest west of the sun in the sky), mercury rises about 1 1/2 hours before sunrise.

At greatest eastern elongation (when the planet is farthest east of the sun in the sky), mercury sets about 1 1/2 hours after sunset.


Mariner 10 view of Mercury, March 29,1974 from

125,000 miles away


Mercury, Mariner 10

photo.

Large valley to right is 4

miles wide and 60 miles

long.

It leads into crater 50

miles in diameter.


Mercury.

Picture taken form 3700

miles away.

Relatively level surface

resembles mare regions of

moon.


Mercury.

Long scarp

diagonally

across picture.


Mercury.

Crater at lower

left is 40 miles in

diameter.

Slows flow front

extending across

crater floor.


Differences between the Moon and Mercury

1. Areas between craters on Mercury smoother than on Moon.

2. Secondary impact craters don't scatter as much on Mercury.

3. Gravitational acceleration on Mercury twice that of moon.

4. Mercury has scarps - caused by shrinkage of its surface.

5. Mercury's atmosphere consists of sodium and potassium (sputtered form surface by the solar wind), helium and oxygen.

6. Atmospheric pressure about the same as on the Moon.

NATS1311 From the Cosmos to Earth Properties of Waves Period: time to complete one cycle of...

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