Diff Geo Unit 4

Chapter 28 pages 747-752, chapter 29 pages 793-795, chapter 30 pages 813-

827, and chapter 31 pages 839-851

CHAPTER 28PAGES 747-752

Radiation

• Light travels in the form of electromagnetic radiation

• We see only visible light.• Electromagnetic radiation is measured by

wavelength.• Shorter the wavelength, the stronger the

radiation.

Electromagnetic Spectrum

Telescopes

• A telescope collects light.• 2 types we use:• 1. refracting telescopes use lenses to focus

visible light• 2. reflecting telescopes use mirrors• Most of our telescopes are reflectors.• Interferometry is linking telescopes together

to act as one

• We’ve explored space with satellites and sent man into space on spacecraft.

• NASA technology has been passed onto commercial industries for common use

• This is called spinoff

CHAPTER 29PAGES 793-795

Formation of solar system

• 1. Interstellar cloud of gas (hydrogen and helium) and dust

• 2. Due to gravity, condensing began and concentrated the mass in areas

• 3. Rotation increased as condensed areas gained mass and formed a disk shape

• 4. The sun formed from the center of this nebula

• 5. Areas around the sun cooled, more so further away

• 6. Substances formed in both liquid and solid form depending on their distance from the sun

• 7. Accumulation of condensed particles formed planetessimals

• 8. Planetessimals merged to form planets, asteroids are the pieces leftover

CHAPTER 30PAGES 813-827

• The sun gets its energy from hydrogen fusion.• H + H --> He• The sun is 70% H and 28% He• The sun has two zones:• 1. Radiative zone comes out from the center• 2. Convective zone on the surface

3 Types of Spectrum

• 1. Continuous- has no breaks in it• 2. Absorption- dark bands within• Caused by a cooler gas in front of the source• 3. Emission- all dark with colored bands at

certain wavelengths

Constellations

• Groups of stars• 88• Appear to move around the north pole• Groups of stars gravitationally bound to each

other called clusters• Two stars gravitationally bound to each other

called binary stars.

Position and Distance

• 1 light year = 9.41 x 10^12 km• Parallax- the apparent shift in positions of a

star because the observer is the one moving• The Earth orbits the Sun, so stars look like

their moving

Properties of Stars

• Magnitude- how bright it appears• Apparent magnitude- The brighter it looks from

Earth, the more negative it’s #• Absolute magnitude- how bright the star is from

10 parsecs• Luminosity- measure of the star’s energy output• The star’s mass determines its temp, luminosity,

and size/diameter

Spectra

OBAFGKMOh be a fine guy/gal, kiss me!• O is the hottest• M is the coolest• The sun is a G2 star

Shifting of spectral lines

• When a star’s spectra is shifting to different wavelengths, this means it is moving

• If the spectra shifts towards the blue (shorter) wavelengths, the star is moving towards us

• If it shift towards the red (longer) wavelengths, then the star is moving away

HR Diagram

• Plots absolute magnitude (Y axis)• Plots Spectral Type (X axis)

• What does that really mean?• The X axis is the temp (hotter, left and cooler,

right)• The Y axis is how bright it is (brightest, top and

dimmest, bottom)

Star Life Cycle

• 1. nebula- cloud of gas and dust• 2. Rotation causes formation of protostar• 3. Once it is hot enough for H to fuse into He,

main sequence stage occurs• This is the longest stage of a stars life.• 4. In medium sized stars, once all H has been

fused into He, He then starts to fuse into C during the Red Giant stage

• 5. Once it’s used up all the He in its core, then the star shrinks and becomes a white dwarf

• 6. Later as it continues to die, it will become a black dwarf

Large Stars

• After the main sequence stage, these stars will undergo a supernova

• After this, they could either form a neutron star after everything collapses or a REALLY large star will become a black hole

• Both are extremely dense

CHAPTER 31PAGES 839-851

The Milky Way Galaxy

• Spiral shape• Bulge surrounded by a halo of spiral arms

Other types of galaxies

• Elliptical• Divided into subclasses based on apparent

ratio of their major and minor axes• Irregular• No distinct shape• Most galaxies are clustered into groups

Is the universe expanding?

• Hubble says yes• V=Hd• V= speed• H= Hubble’s constant• H= 70 km/s/mparsec • D= distance in mega parsecs• The greater the distance, the faster its moving

away.

Big Bang Theory

• The universe began as a point, expansion occurred, and has been expanding ever since

• Evidence:• Cosmic (microwave) background radiation• Quasars• Red shift

Evidence #1

• Cosmic (microwave) background radiation detected by antennae in 1965 coming from all directions in space

• The emitter of this radiation has a temperature of that predicted by the big bang theory

• Therefore scientists interpret this to be coming from the beginning of the big bang

Evidence #2

• Quasars • Most stars are not strong radio emitters• Quasars are, and were discovered in the 1960s• Quasars emit spectra lines of common elements with

longer wavelengths ex: H• The redshift of quasars is much longer than any other

galaxy, which means they are the farthest away• This associates them with the timing of the big bang

Evidence #3

• Red shift• Edwin Hubble saw that galaxies are moving

away from earth based on the red shifts he saw in 1929

• In a medium that is uniformly expanding, all points are moving away from all other points, and no point has to be at the center

Will the expansion of the universe stop?

• Competition between outward momentum of the expansion of the universe and the inward force of gravity

• Density is higher than critical density= closed universe

• Density is lower than critical density= open universe

• If they equal each other, the universe is flat.

• Astronomers have discovered that the rate of expansion is speeding up

• The only explanation offered so far is that a previously unknown force is acting to push the galaxies apart

• This unknown force is dominating over gravity