Astronomy 101 Study Guide PDF

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Study Guide of all the lecture notes given and possible questions from the test
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Astronomy 101 Study Guide A. MOTION OF THE SUN, MOON AND STARS a. Sun: i. Sun rises in the east and sets in the west ii. Earth travels around the sun (REVOLVES [orbit] once a year around the sun) iii. Earth rotates counterclockwise (west to east) iv. The plane of the earth's orbit is called the ecliptic. Since the earth orbits the sun, the sun is also on the ecliptic. As a result, the sun appears to us to move around the sky on the ecliptic. v. Takes a year to go around ecliptic b. Moon i. The moon rotates from north-south axis ii. Rises in the east and sets in the west iii. Moon orbits Earth iv. Earth-Moon system orbits the sun v. Moon always keeps the same face toward Earth vi. Synchronous Rotation  It takes exactly as long for the Moon to rotate on its axis as it does to make one orbit around Earth. (It returns to the same position and that’s why we only see one face all the time) vii. 4 Weeks  One set of phases c. Stars i. Diurnal Motion  Daily motion of stars across the sky relative to Earth’s rotation ii. Circumpolar Stars  Stay in the same place, too far from the horizon, never set iii. Stars rise in the east and set in the west iv. Motion of stars caused by Earth’s rotation v. As Earth turns from west to east it appears to the observer that the celestial sphere turns from east to west. B. WHY DOES EARTH HAVE SEASONS? a. Seasons are caused by the tilt of Earth’s axis of rotation b. Earth rotates on its axis every 24 hours c. Earth’s axis of rotation is tilted with respect to its orbit. d. During (northern) summer, the northern hemisphere is tilted toward the sun. This makes the Sun’s light hit the northern hemisphere at a nearly perpendicular angle, making the energy more concentrated, which makes it warmer

e. In winter, the northern hemisphere is tilted away from the sun. This makes the sun’s rays hit the northern hemisphere at a larger angle, spreading out the energy, and making colder.

C. SIDEREAL/SOLAR DAYS? a. Sidereal Day  Time taken by the earth to rotate on its axis relative to the stars (they appear to be in the same position), and is almost four minutes shorter than the solar day because of the earth's orbital motion b. Solar Day  The time it takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky (24 Hours) c. Solar Day is longer because after one sidereal day, Earth has moved its orbit around the Sun. Thus, Earth will have to rotate a little bit more to return the Sun to the same spot in the sky.

D. PHASES OF THE MOON

E. ECLIPSES a. Eclipses only occur when the sun and moon are both on the line of nodes b. Eclipses  When the sun, earth, and moon all align on a straight line. The shadow of earth falls on the moon, or the shadow of the moon falls on earth. c. Lunar Eclipse  Moon passes through earth’s shadow, the earth is between the sun and moon (Moon goes into earth’s shadow) i. Umbra  No portion of the sun’s surface can be seen from the moon (complete shadow, all light is blocked) ii. Penumbra  A portion of the sun’s surface is visible (partial shadow, part of the light is blocked) i. Penumbral Eclipse  Moon in penumbra (BAD) iii. Total Lunar Eclipse  Moon is red (part of moon in umbra) iv. Partial Lunar Eclipse  Occur at full moon d. Solar Eclipse  Earth passes through the moon’s shadow and moon moves in front of the sun. The moon is in between the earth and the sun) Happens only at new moon. (Earth in moon’s shadow) i. Partial Solar Eclipse  Moon’s penumbra covers earth’s surface and anyone standing inside it sees a partial solar eclipse ii.

Total Solar Eclipse  You are in umbra and is very short (GOOD) If you were on the moon during this time, the moon casts a shadow on Earth,

but the shadow is much smaller than Earth, so it would only be a relatively small spot. e. For eclipses to happen, moon must lie in the same plane as earth’s orbit around the sun and on ecliptic.

F. KEPLER’S & NEWTON’S LAWS/GRAVITY/TIDAL FORCES a. Kepler’s Laws i. Planets orbit in ellipses i. 0  circle ii. 1  Not coming back (ellipses will never close) ii. Planets carve out equal areas in equal times i. Planets move faster at closer points of orbit iii. The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun i. Orbit  How far away it’s from the sun b. Newton’s Laws i. Objects in motion tend to stay in motion. If no force acts on an object, then there will be no acceleration (change in velocity) ii. The bigger the force, the bigger the acceleration iii. For every force, there is an equal and opposite force c. Gravity  If it has more mass and if it’s closer, then the object has stronger gravity. The force that attracts a body toward the center of the earth, or toward any other physical body having mass i. The bigger the distance, the smaller the force ii. The bigger the mass d. Tides i. Tidal forces exist because gravity is stronger at closer distances ii. So, when a planet is near another object, the side of the planet nearest the object feels the strongest pull of gravity, and the far side feels the weakest force of gravity. iii. The effect of this is to stretch out the planet iv. On earth, since it is rigid, the effect is to stretch out the oceans, causing two high tides and two low tides

v.

Moon and sun stretch earth for super big waves i. Spring Tides (side of earth)

ii. Neap Tides Small tides characterized by the 1st and 3rd quarter moons

G. HOW DOES LIGHT WORK/BLACKBODY RADIATION/TYPES OF SPECTRA AND HOW THEY ARE CREATED/DOPPLER SHIFT a. b. c. d. e. f.

Light is pure energy and has no mass High energy photon  high frequency  short wavelength Low energy photon  low frequency  long wavelength White light is a combination of all the colors of the spectrum Light is an electromagnetic wave Wavelength  Equivalent to color (400-700 nm – visible light) i. Shortest – Longest (GXUVIR) ii. Gamma Rays, X-Ray, Ultraviolet, Visible, Infrared, Radio Wave g. Frequency  Number of waves h. Absorption Spectra  The characteristic pattern of dark lines or bands that occurs when electromagnetic radiation is passed through an absorbing medium into a spectroscope i. Emission Spectra Spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state

j. Continuous Spectra  A spectrum of hot, dense objects will emit electromagnetic radiation at all wavelengths or colors (BLACKBODY)

k. Blackbody Radiation  Hot electrical light (DENSE) i. Color changes depending on temperature ii. Light  Electromagnetic Wave is created by moving electric charge iii. Blackbody radiation is light emitted by an object due to its temperature iv. The HOTTER it is the BRIGHTER it is v. The HOTTER it is the SHORTER the peak wavelength

g. Doppler Shift  The change in frequency of a wave for an observer moving relative to its source. i.

Astronomers use the information about the shift in frequency of electromagnetic waves produced by moving stars in our galaxy and beyond in order to derive information about those stars and galaxies

H. REFRACTING VS REFLECTING TELESCOPES/GOOD & BAD POINTS

a. Refracting Telescope  A type of optical telescope that uses a lens as its objective to form an image. It uses a glass lens as its objective. The glass lens is at the front of the telescope and light is bent (refracted) as it passes through the lens

ii.

Good Points 1. Refractor telescopes are rugged. After the initial alignment, their optical system is more resistant to misalignment than the reflector telescopes. 2. The glass surface inside the tube is sealed from the atmosphere so it rarely needs cleaning. 3. Since the tube is closed off from the outside, air currents and effects due to changing temperatures are eliminated. This means that the images are steadier and sharper than those from a reflector telescope of the same size. iii. Bad Points 1. Difficult/expensive to make the lens flawless throughout 2. Lens absorbs some light 3. Chromatic Aberration Different wavelengths of light focus to different points 4. Large lenses sag under their own weight and stop working 5. Size is LIMITED! b. Reflecting Telescope  An optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. c. All celestial objects (including those in our solar system) are so far away that all of the light rays coming from them reach the Earth as parallel rays. Because the light rays are parallel to each other, the reflector telescope's mirror has a parabolic shape.

d. The parabolic-shaped mirror focusses the parallel lights rays to a single point. All modern research telescopes and large amateur ones are of the reflector type because of its advantages over the refractor telescope. i. Good Points 1. Reflector telescopes do not suffer from chromatic aberration because all wavelengths will reflect off the mirror in the same way. 2. Support for the objective mirror is all along the back side so they can be made very BIG! 3. Reflector telescopes are cheaper to make than refractors of the same size. 4. Because light is reflecting off the objective, rather than passing through it, only one side of the reflector telescope's objective needs to be perfect. ii. Bad Points 1. It is easy to get the optics out of alignment. 2. A reflector telescope's tube is open to the outside and the optics need frequent cleaning. 3. Often a secondary mirror is used to redirect the light into a more convenient viewing spot. The secondary mirror and its supports can produce diffraction effects: bright objects have spikes (the ``Christmas star effect'').

I. OBSERVATORY LOCATION/WHICH TYPES OF LIGHT PENETRATE OUR ATMOSPHERE a. Observatory Location (MUST HAVES) i. High Altitude  Light passes through less atmosphere, so less distorted ii. Dry Climate  Clouds block the sky iii. Away From Cities & Light  Less light pollution (light from people) iv. Near the Ocean  Smooth air flow

b. Types of Light that Penetrate Atmosphere i. ENTIRELY  Visible light and radio ii. PARTIALLY UV and infrared iii. CANNOT  Gamma and x-rays J. HOW ARE THE PLANETARY MAGNETIC FIELDS CREATED? a. MUST HAVE: i. Electrically conducting fluid ii. Quick rotation (Earth rotates once a day) b. Example  In Earth, there is a molten iron core and its spinning around and since core is conductive, then it has a magnetic field. K. WHY DO YOU NEED A SPACESUIT IN SPACE? a. b. c. d.

Need to breathe because there is no atmosphere Lack of pressure (imbalance of you and the outside) it would hurt No ozone  Absorbing all UV light, so you would get an instant sunburn Temperature sucks  Sunlight is baking hot and night is freezing cold

L. HOW DID THE SOLAR SYSTEM & PLANETS FORM? a. Formation Hypothesis i. Must match observation ii. Planets orbit in the same direction and plane iii. Inner planets are small and rocky iv. Outer planets are big and gaseous v. Little stuff (Oort Cloud & Kuiper Belt) b. Nebular Hypothesis i. Solar system formed from a nebula (large cloud of gas and dust) ii. Nebula is compressed and therefore the gravity gets stronger and atoms get closer and nebula contracts and collapses. iii. Nebula collapsing causes: 1. Heating  Gravitational energy  Thermal energy 2. Angular Momentum  Has to be conserved as nebula gets smaller 3. Spinning  Conservation of angular momentum, throwing things out and therefore a disc forms around center/equator 4. Disk Formation  Rotation causes disk of material to form around “equator” of central proto sun. c. Planet Formation i. Fusion can happen

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Inner Solar System 1. Ices are GONE  Only rock remains 2. ACCRETION 3. Growing by accumulating material (Example  Building a snowman, has a ball and rolls it around and it gets more snow  bigger) 4. Bits of rock collide, stick together via molecular bonds 5. Grow larger over time (1 mile across = planetesimals) 6. Gravity attracts rock 7. Gravity holds object together (rock  planet) 8. Earth is round because gravity is pulling from all directions 9. Rock stops growing when all rock has been accreted Outer Solar System 1. The protoplanetary disk originally contained gas (H, He), dust, rock and ices 2. In the outer solar system, the Sun was far away, so the temperature was low, and the ices survived 3. The ice and dust particles orbited the sun, occasionally colliding, and sticking together via molecular bonds 4. Slowly these collisions would occur, and the particles would accumulate and grow to larger sizes 5. When they grew to asteroid sizes, their large mass meant that gravity became the dominant force keeping the objects together and also attracting other pieces of ice/rock. 6. Gravitational accretion then continued until the planetesimals grew into the size of planets. 7. These planets had enough gravitational force to accrete the gas from the disk, since the disk was cold, making the gas molecules move slowly 8. By accreting gas, they grew in to gas giants

M. THE MOONS SURFACE/MARIA AND HIGHLANDS a. Dark Regions (Maria) i. Few craters  Iron rich rock  Gives it a darker color ii. Craters nearly reach the mantle iii. Lava seeps into crater, cools, and hardens into smooth surface b. Light Regions: Highlands i. Lots of craters  Iron-poor c. Far side of the moon

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i. ALL highlands Moonquakes i. Very small ii. Caused by Earth’s tidal forces (stretch solid moon) Virtually no erosion i. No geological activity ii. No atmosphere or H2O iii. Only source of erosion  Micrometeorites  Like grains of sand Regolith i. Fine powder covering lunar surface ii. Created by MANY micrometeorite impacts Moon is dry i. Rocks have no H2O ii. H2O becomes gas in the sun iii. Some ice is hiding in craters near the poles Tiny part of core is liquid i. BUT it has a slow rotation  NO magnetic field

N. HOW DID THE MOON FORM? a. Moon was formed when a Mars-sized object slammed into the Earth, billions of years ago b. This collision turned the newly formed Earth into a molten ball of rock again, and ejected material into orbit c. Most of the material crashed back into the Earth, but some collected together from mutual gravity to form the Moon we have today. d. After an impact from a Mars-sized planet, the lighter outer layers of the Earth would have been ejected into orbit and coalesced into the Moon, while the denser elements collected back together into the Earth

O. THE TERRESTRIAL PLANETS (INTERIOR, SURFACE FEATURES)/PLATE TECTONICS (EARTH)/ATMOSPHERES (GREENHOUSE EFFECT, HISTORIES)/WHY EARTH’S SKY IS BLUE/ANYTHING UNIQUE ABOUT PLANET/WATER ON MARS a. Mercury

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Surface 1. Has lots of craters, plains (like maria on moon) 2. Really huge cliffs that form after plains, craters 3. Cliffs formed because as Mercury was cooling off, crust contracted and split open 4. Caloris Basin  Plain (impact basin) 5. Impact created jumbled terrain on opposite side of the planet Interior 1. Mercury has huge core  Best hypothesis based on Mercury’s density (Know density through gravitational pull) 2. Mercury is small 3. Interior should be cool & partially molten (wobble) 4. Slow rotation 5. NO magnetic field

b. Venus i. Surface 1. Sulfur in atmosphere (thicker and denser) 2. Clouds are sulfuric acid (battery acid)  Acid rain 3. So hot that battery acid evaporates before reaching surface 4. Active volcanism 5. ALL shield volcanoes 6. NO plate tectonics because the crust is too soft to form rigid plates due to hot surface ii. Interior 1. Quite similar to earth’s 2. Formed a differentiated core with the heaviest elements such as iron sinking to the middle of the planet 3. The mantle is probably rocky, and the core is probably somewhat liquid. c. Mars i. Surface 1. No plate tectonics 2. Volcanoes, but not active 3. No magnetic field  It did have one in the past, but because mars is so small, it cooled and liquid core solidified 4. No liquid H2O because there is little atmospheric pressure (either gas or solid) 5. Small amount of water in the atmosphere

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6. River channels, flood channels, flood plains, lake beds Interior 1. Some water in polar ice caps (layer of frozen water and later of CO2 on to) 2. Permafrost (underground ice) 3. No magnetic field Atmosphere 1. Started out like Venus & Earth a. Volcanic outgassing (CO2 & H2O) b. Carbon cycle c. Outgassing d. Rain down into oceans e. Subduction 2. BUT mars is small and interior cooled 3. No plate tectonics 4. No volcanoes a. CO2 comes down in rain but no outgassing to replenish it b. Greenhouse effect weakens c. Temperature gets colder d. More rain e. Eventually much of the atmosphere is gone 5. No magnetic field a. No magnetosphere to protect you from the solar wind b. Solar wind blows away remaining atmosphere 6. UV breaks apart H2O a. H too light so it escapes b. O2 is heavy and oxidized ricks (rusted surface rocks from mars and is why its red) 7. At poles, CO2 freezes out of the atmosphere in winter  Covers the ground in several meters of dry ice Earth’s Atmosphere 1. No H, He to start with because they were so light that they escaped 2. Original atmosphere was CO2 + H2O which came from volcanic outgassing 3. Strong greenhouse effect (pretty warm) 4. CO2 dissolves in rain a. Rains down to surface b. Carbon becomes part of ocean floor rock

v.

c. Ocean floor is subducted into mantle d. CO2 is emitted into atmosphere by volcanoes (then starts cycle over again)  CARBON CYCLE 5. Life appears and uses photosynthesis (sunlight, CO2 and H2O) to emit O2 as a waste product 6. Life evolves to use O2 for respiration to emit CO2 Greenhouse Effect 1. The sun mostly emits visible and infrared light. Only visible light makes it through the atmosphere, and is absorbed by the surface of Earth 2. The warm surface then re-emits the energy as blackbody radiation, mostly infrared light 3. IR light, however, is absorbed by greenhouse gases in our atmosphere and thus trapped near the surface of the Earth and reemitted, warming the surface of the earth even more....