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Week 27 – Stars_ Eclipses _ Constellations

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					Week 27 – Stars, Eclipses & Constellations I. Eclipses A. Moon’s orbit slightly tilted with respect to Earth’s orbit around sun 1. most months, moon revolves around Earth w/o moon moving into Earth’s shadow or moon’s shadow hitting earth B. Eclipse occurs when moon’s shadow hits Earth or Earth’s shadow hits the moon C. Eclipse occurs when an object in space comes between the sun & a 3rd object, & casts a shadow on that object D. Two types 1. Solar eclipse a. occurs when the moon passes between Earth & the sun, blocking the sunlight from reaching Earth b. really just a new moon in which the moon blocks view of sun c. Total Solar Eclipse 1.) Umbra – darkest part of moon’s shadow a.) cone shaped b.) from any point in umbra, light from sun completely blocked by moon 2.) only people within umbra experience total solar eclipse 3.) during solar eclipse see stars & solar corona(faint outline of sun’s atmosphere) d. Partial Solar Eclipse 1.) Penumbra – moon cast another shadow that is less dark than the umbra – this larger part of the shadow called penumbra a.) part of sun is visible from Earth 2.) people in penumbra see only partial solar eclipse 2. Lunar Eclipses a. occurs only at a full moon when Earth is directly between the moon & sun b. Earth blocks sunlight from reaching the moon c. because moon is in Earth’s shadow, it looks dark from Earth d.. Total Lunar Eclipse 1.) when the moon is in Earth’s umbra, see total lunar eclipse 2.) lunar eclipse can be seen anywhere on Earth that the moon is visible e. Partial Lunar Eclipse 1.) occurs when Earth, the moon, & the sun are not quite in line 2.) occurs when moon passes partly into the umbra of Earth’s shadow 3. Tides a. occur mainly because of differences in how much the moon pulls on diff. parts of Earth Characteristics of Stars I. Introduction A. Galaxy – cluster of stars B. Milky Way – our galaxy C. Andromeda Galaxy – another one nearby D. Universe contains billions of galaxies a. defined as all of space & everything in it b. most of universe is empty space II. Distances to stars A. Lightyear – used to measure distance in space 1. light travels at speed of 300,000 K/sec 2. Def.- distance that light travels in one year, or about 9.5 million million kilometers 3. lightyear is a unit of distance, not time

III. Measuring distances to stars A. Parallax – apparent change in position of an object when you look at it from different places 1. how used to measure distance to nearby stars a. look at a star when Earth on one side of the sun & then look at same star 6 months later b. measure how much star appears to move against background of stars farther away. c. use this measurement, called parallax shift, to calculate how far away the star is. d. the less a star appears to move, the farther away it is. IV. Classifying stars A. huge spheres of glowing gas – like the sun 1. mostly hydrogen 2. make energy by nuclear fusion 3. sun – only avg. brightness star a. not brightest nor largest in galaxy b. appears brighter & larger because closer B. Classify according to physical characteristics 1. main characteristics used to classify stars are size, temperature, & brightness C. Size of stars 1. many are size of sun – medium size star 2. Giant stars or supergiant – very large a. Betelgeuse – supergiant 3. white dwarf – small -  size of Earth 4. Neutron star – even smaller -  20 k in diameter D. Color & temperature of stars 1. color of star reveals its temperature a. coolest to hottest – red  yellow-white  blue-white 2. coolest stars -  3,200 C – appear reddish (ex. Betelgeuse) 3. glow white – stars  5,500 C 4. hottest stars – over 10,000 C – slightly bluer that the sun (ex. Rigel – appears blue-white) E. Brightness of stars - amount of light they give off 1. depends upon size & temperature 2. how bright a star looks from Earth depends on how far the star is from Earth & how bright the star actually is - described in two ways 3. Apparent Magnitude a. brightness of star as seen from Earth b. cannot tell how much light a star gives off just from apparent magnitude 4. Absolute Magnitude a. the brightness the star would have if it were at a standard distance from Earth F. Hertzsprung-Russell Diagram 1. two most important characteristics of stars - temperature & absolute magnitude 2. graph made to find out if temp. & brightness are related 3. most stars in H-R diagram form a diagonal band called the main sequence 4. in the main sequence, surface temp. increases as brightness increases a. sun in main sequence b. giant & supergiant – higher & further to right on H-R c. white dwarfs are hot, but not very bright, so appear at bottom center of H-R diagram


				
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