1. Our View from Earth
Ch 22 p. 800

2. 22.1 Our View from Earth
Stars seem to move but Earth is actually moving west to east
So objects in the sky seem to rise in the east & set in the west
North star, Polaris is above North Pole and stars around it seem to form a circle-always present in Northern hemisphere
Ancient scientists began observing the sky with their eyes only
They used objects to tell time and find directions

3. Constellations Ancient astronomers noticed patterns in the night sky
Ptolemy identified many patterns of stars - constellations over 2000 years ago
Today’s astronomers used constellations to divide the sky into 88 regions
Vary throughout the seasons as Earth revolves and rotates
Many resemble people, animals, or objects
Ex: Big Dipper, Lil Dipper, Twins, Orion the hunter, Draco the dragon

4. Telescopes
Collect much more light than human eye but visible light is one small part of radiation that is studied
Electromagnetic spectrum is a continuous range of wavelengths of radiation (visible & invisible)
Long wavelengths = low energy Short wavelengths = high energy
As different objects in space give off wavelengths, telescopes collect and interpret data
Spectroscopes spread light into different wavelengths to study stars
Characteristics studied: temp, composition, energy, life cycle, etc… Know chart p. 803

5. Measuring Distances in Space
Astronomical unit-distance between Earth and the Sun (150 million km)-used to measure within the solar system
Light year -distance light travels in one year (300,000 km per second)-used to measure beyond solar system
Parallax -the change in an object’s position caused by looking at it from two different points - uses changes in angles
The farther away an object, the longer it takes for its light to reach Earth

6. Measuring Brightness in Space
Some stars seem dim while others seem bright - astronomers compare appearances from Earth to the actual appearance of stars
Luminosity is the true brightness of an object (metals, jewels, stars, etc)
Apparent magnitude-appearance from Earth
Absolute magnitude-actual appearance based on luminosity
Distance is related to brightness - dim stars have greater apparent magnitude
Brightest star: Sirius Chart p. 805

7. 22.2 Nuclear Fusion
Nuclear fusion is a process that occurs when the nucleus of several atoms combine into one larger nucleus-this occurs due to atoms moving very fast.
Hot means atoms move fast Cold atoms move slow.
Massive amounts of energy is released in nuclear fusion
Nuclear fusion occurs on hot stars (millions of degrees)
The energy leaves the star’s core, and travels throughout space making it appear to shine

8. Structure of Stars
Sun is closest star to Earth and it is easily observed/studied
Sun and other stars are typically made up of the gases hydrogen and helium
Stars have life cycles: born, grow, die
Star is a large ball of gas held together by gravity with a core so hot that nuclear fusion occurs.

9. Layers of the Sun Core is made of helium
Radiative zone-shell of cooled hydrogen above the core
Convection zone-where hot gas moves towards surface and cooler gas moves toward center
Photosphere-surface of a star - part seen - made of gas
Chromosphere-orange/red layer above photosphere
Corona-wide outermost layer of star’s atmosphere - hottest temps
Analyze pic p. 810

10. Changing Features
Interior (core, radiative & convection) stable Analyze pictures p. 811
Atmosphere can change though
Other changes: sunspots-regions of strong magnetic activity
Prominences & flares-loops of gas clouds & sudden increase in brightness
Coronal Mass Ejections (CMEs)-huge bubbles of gas coming from the corona
Solar winds-created by charged particles streaming away through solar system
Auroras-curtains of light created from solar winds in both hemispheres “northern lights”

11. Grouping Stars Star closest to the Sun is 4.2 light years away
Some stars are single (sun) and some exist together
Binary system has 2 stars orbiting one another
Clusters are more than 2 stars: Open -formed same time and distance from Earth-up to 1000
Globular-hundreds of thousands of stars
Most stars are smaller than the sun

12. Classifying/Grouping Stars
Different temps = different colors
Red is the coolest; Orange, Yellow, Blue, White is the hottest
Smallest is a red dwarf
Massive stars are usually the hottest (blue/white)
Most stars spend the majority of their lives on the main sequence-where mass of star determines temp & luminosity
High mass stars = shorter life cycle Low mass stars = longer life cycle

13. Hertzsprung-Russell diagram
A graph that plots luminosity and temperature of stars (see p. 813)
Used to characterize stars
X axis shows decreasing temps Y axis shows increasing luminosity
If astronomers know a star’s luminosity ,they can calculate distance from Earth using a mathematical formula

14. 22.3 Evolution of Stars
All stars form the same way but die differently depending on their masses
Nebula-a cloud of dust and gas is where astronomers think stars come from
Main sequence is most of star’s life when they are fusing hydrogen into helium at the core
Death is when stars do not have any more hydrogen. Massive stars collapse & explode. Dwarfs lose their gases and expose their cores slowly.
When stars die, their matter escapes into space and eventually form new stars

15. Supernova
An enormous explosion that destroys a star when iron forms in the core - loses internal energy source
When stars explode, a star becomes brighter and heavier
Supernova is when star’s outer layers are blown away leaving exposed core
The sun remains on main sequence for 5 billion more years
When the sun becomes a white dwarf, the solar system will be a dark and cold place

16. Neutron stars
Atoms are mostly empty space Protons & electrons combine to form neutrons.
Neutrons are neutral particles (not positive or negative) in the nucleus (middle) of an atom
Neutron stars are stars with dense cores of neutrons that remain after a supernova.

17. Black Holes
An object whose gravity is so great that no light can escape
Formed when gravity is too strong and all matter (solid/liquid/gas/plasma) crushes
All the gravity is concentrated in a single point
Not able to see
Located when objects like stars are circling around an invisible force

18. 22.4 Galaxies & Universe
A galaxy is a huge collection of stars; contains hundreds of billions of stars
Universe contains hundreds of billions of galaxies
Gravity holds it all together
Galaxies are not distributed evenly in the universe-some are grouped in clusters
Most matter in galaxies is invisible and called dark matter
90% universe is dark matter

19. Types of Galaxies
Spiral-symmetrical spiral arms; some long and some short; thicker near center; looks hazy
Elliptical-no internal structure, not much gas or dust
Irregular-oddly shaped; many young stars
All contain stars, gas and dust in different amounts
See pictures on p. 826

20. The Milky Way Our galaxy is called the Milky Way
Spiral galaxy with gas, dust, and 200+ billion stars
Clustered with 30 other galaxies
Andromeda is the largest galaxy

21. Big Bang Theory Theories cannot be proven or disproven
BBT predicts that the universe began from one point billions of years ago and has been expanding ever since. Some scientist predict gravity pulled dust together immediately to form the universe.
Scientist have discovered that the universe is slowly expanding and stretching - detected by galaxies moving away from Earth.
Wavelengths change as galaxies move

22. Doppler Effect
As scientist analyze light and radiation in space, the type of wavelength determines if it is moving away or towards Earth.
Long wavelengths mean moving away
Short wavelengths mean moving toward
Doppler is also used to detect and predict storms and weather

23. TEST TIME Vocab Power Point Main Ideas p. 834 Review p. 835-837
Good Luck!