Our View from Earth Ch 22 p. 800

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

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

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

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

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

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

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.

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

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”

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

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

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

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

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

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.

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

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

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

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

Big Bang Theory Theories cannot be proven or disproven BBT predicts that the universe began from one point 13-14 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

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

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