M+P-Mid-Term Review Mid-term Review

Term Definition Contribution of Eratosthenes -Computed circumference of Earth-Sun is directly overhead at noon day Why did Aristarchus’s argument fail? -Followed the Heliocentric Model, but was challenged by astronomers and Aristotle Retrograde motion (wrong interpretation) Wrong- Ptolemy–> hard to explain with a model of an unmoving earth at center of universe–> epicycles- explain odd motion of given planets by a small circle Retrograde motion (correct interpretation) Correct- Copernicus –> created Heliocentric Model (the sun is the center of universe) –> retrograde motion was a prospective effect Standard notation for large numbers EX) 1.5 X 10^6 = 1,500,000 Convert: miles to km km to miles 1 mile = 1.609 km 1 km = .621 miles Compute time for Sun's light to reach planets knowing Solar Distance to planets in Astronomical Units (speed of light problem) average distance from Earth-Sun = 1.5 X 10^8km (look on quiz 1 for more help) Apparent Visual Magnitude scale for stars -15 = you can see (-) = brighter (+) = fainter (harder to see) Significance of observing Stellar Parallax Early Astronomers believed Earth didn't move because they saw no parallax Magnitude of distance in light years to nearest galaxy Andromeda Galaxy is 2.5 X 10^6 light years from Earth -The light we see from the galaxy, left before evolutionary ancestors became human Perihelion versus Aphelion Perihelion- The orbital point of closest approach to the sunAphelion- The orbital point of greatest distance from the sun Be able to calculate Sun angle for equinoxes knowing latitude position in degrees 0 degrees at equator; 90 degrees at north pole; -90 degrees at south*@equinox- 90 (degrees at n.pole) – 42.5 (fred lat) = 47.5 (noon day angle)*@summer solstice- 47.5 (noonday angle at fred) + 23.4 =(max sun angle distance Solar Day vs. Sidereal Day Solar: 24 hour day (clock time); based on Sun's movement Sidereal: 23 hours, 56 min – Earth's rotational period based on fixed stars -This is because the Earth and the Sun are both moving relative to the celestial sphere Ecliptic Plane Zodiac Belt contains constellations through which the Sun, Moon, and planets move in annual cycle Know the Lunar Phases Co-rotation of Moon with Earth (tidal lock) -What does this explain? "Face on the Moon"- only see one side of it -experience tides by gravity of the moon Why are eclipses infrequent? Moons orbit is 5 degrees off of Sun- Earth ecliptic plane -Moon is always near ecliptic, but slightly North or South of it Umbra vs. Penumbra umbra- total dark shadow (totality)penumbra- partial eclipse Full Solar Eclipse Moon completely covers the bright surface of the sun Annular Eclipse-What can't be seen during this time? Solar eclipse when the solar photosphere appears around the edge of the moon in a bright ring-The corona, chromosphere, and prominences can't be seen Copernicus's Universe Model INACCURATE- includes uniform circular motion and doesn't describe motion of planets BUT- Heliocentric hypothesis is correct!And reterograde motion is the perspective effect Kepler's 1st Planetary Law All planets move in elliptical orbit with the sun at the focus Kepler's 2nd Planetary Law The line joining the planet and the Sun sweep out the equal area during equal areas of time Kepler's 3rd Planetary Law For planets, the square of its period of revolution is proportional Be able to calculate the orbital period of a given planet knowing its Solar Distance Kepler's 3rd law a^3= p^2 How did Galileo's telescope observations advance science?Moons of Jupiter -4 "New" planets circling Jupiter **If moon orbits Jupiter, then the Earth orbits the Sun -supported Kepler's 3rd law Phases and disc size variation in Venus -goes through phases like the moon -had heliocentric orbit Closed Orbit vs. Open Orbit Closed- An orbit that returns to its starting point (circular or elliptical orbit)Open- An orbit that does not return to its starting point (escape orbit) Concept of an orbital Center of Mass between two orbiting objects -2 bodies of different mass balance at the center of mass (located closer to the more massive object)EX) Earth-Moon – Moon orbits center of mass on one side, Earth swings around center of mass on opposite side Newtonian Inertial Motion Concept (1st law of motion)-An object at rest stays at rest until acted on by some forcef=ma What situation produces a Spring Tide, and what situation causes a Neap Tide? Spring Tide- rising up of water; occurs at full and new moonNeap Tide-less extreme tides; occurs at 1st and 3rd quarters Be able to explain the Foucault Pendulum concept and its significance -Proof of Earth's rotation and illustrates Newton's 1st law(Pendulum illustrates inertial motion)-We are moving around the axis of Earth (revolving)-We are going in a colossal circle that will return to original orientation Refracting Telescope and its limitation (be sure to find this info) -forms images by bending (refracting) light with a lenslimitation: chromatic aberration -looks distorted Reflecting Telescopes and their advantage -uses concave mirror to focus light onto imageadvantage: reflecting off mirror-sharply reduce blur of image Optical Telescope Gathers and focuses visible light**this light is seen** Radio Telescope Gathers and focuses electromagnetic energy with microwave and radio wavelengths Concept of "Light Gathering" as real measure of telescope power power of telescope is important for light capability **magnification is not as important Significance of Bright Line (Emission) Spectra A low-density gas energized at specific wavelengths Significance of Dark Line (Absorption) Spectra happens when radiation passes a cool, low-density gas EX) light bulb surrounded by gas –> atoms in gas absorb photons of wavelengths and see dark lines What is the Doppler Effect and how is it significant? Apparent wavele from light or sound of light that travels at the speed of light -redshift- longer wavelength -blueshift- shorter wavelength How are different true stellar distances expressed in terms of stellar parallax? What do the very long and variable times of exposure of film needed to get images of the Milky Way, Andromeda, and other galaxies tell us about the Universe beyond our Solar System and stellar neighborhood? The longer time it takes to develop film, the object is farther away -this is why you cana??t see andromeda or galaxies farther away a??Light gatheringa?? Contribution of Edwin Hubble (see red shift of galaxies and expanding universe concept Estimate of the age of the universe is estimated in Hubble Time -universe expanded faster than speed of light -orbiting telescope is called a??Hubblea?? Galactic red shift proportional to distance from Earth Universe is expanding with respect to itself "Big Bang" event If galaxies are moving away from each other with speed proportional to distance -MUST be a beginning when everything was concentrated in one single point

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