Astronomy Test 1 - Lecture notes 1-8 PDF

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Study guide for exam 1 covering lectures 1-8...

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Sun- a large glowing ball of gas that generates heat and light through nuclear fusion Planet- a moderately large object that orbits a star; it shines by reflected light. They may be rocky, icy, or gaseous in composition(exoplanets- planets orbiting other stars) Moon (satellite)- an object that orbits a planet (about 150-200 moons in our own solar system) Asteroid- a relatively small and rocky object that orbits a star Comet- a relatively small and icy object that orbits a star Solar (star) system- a star and all the material that orbits it, including moons Nebula- an interstellar cloud of gas and or dust Galaxy- a great island of stars in space, all held together by gravity and orbiting a common center Universe- the sum total of all matter and energy; that is, everything within and between Astronomical unit (AU)- the average distance from the earth to the sun Light year- the distance light can travel in one year *if sun was grapefruit, earth is 1mm bead, distance would be about 15 m and solar system is campus Constellations- a region of the sky; Groups of stars making an apparent pattern in the celestial sphere (asterism smaller part of a constellation i.e. big dipper) Ecliptic- sun’s apparent path through the celestial sphere - north celestial pole: directly above earth’s north pole - south celestial pole: directly above earth’s south pole - celestial equator: projection of earth’s equator onto sky Local sky- an object’s altitude (above horizon) and azimuth (direction along horizon) specify its location in your local sky Right ascension- like longitude Declination- like latitude on celestial sphere Sidereal day- earth rotates once on its axis in 23 hrs, 56 min • Our clock system is based on the sun** Solar day- the sun makes one circuit around the sky in 24 hrs Sidereal month- moon orbits earth in 27.3 days Synodic month- a cycle of lunar phases, takes 29.5 days, 1/12 longer than a sidereal month Sidereal year- time for earth to complete one orbit of sun Tropical year- time for earth to complete one cycle of seasons. Tropical year is about 20 min (1/26,000) shorter than a sidereal year because of precession (**if there was no tilt, there would be no seasons) Planetary periods- can be measured with respect to stars (sidereal) or to apparent position of sun (synodic) Moon phases- new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third (last) quarter, waning crescent, new moon (waxing = bigger, waning = smaller) Moon is tidally locked to earth- its rotation rate is the same as the time it takes to make one revolution We essentially see the same face of the moon at all times because the Moon’s rotational and orbital periods are equal Synchronous rotation- the moon rotates exactly once with each orbit Lunar eclipse = full moon (Sun,Earth,Moon) Total when Moon is in umbra solar eclipse = new moon (Sun,Moon,Earth) Total when earth in moon’s umbra Copernicus- sun centered model but it was no more accurate than Ptolemaic model in predicting planetary positions because it still used perfect circles (but had a solution to the retrograde/backwards motion) Tycho Brahe- compiled most accurate naked eye measurements ever made of planetary positions but couldn’t detect stellar parallax and thought we has geocentric model (earth centered model) • Johannes Kepler- Brahe’s student (or hired help) Kepler’s first law- the orbit of each plane around the sun is an ellipse with the sun at one focus Kepler’s second law- as a planet moves around its orbit, it sweeps out equal areas in equal times Kepler’s third law- more distant planets orbit the sun at slower average speeds, obeying the relationship: P^2= a^3 P= orbital period in years; a = average distance from sun in AU (aka semi major axis)- (closer to sun = faster; farther away from sum = slower) Speed- rate at which object moves (speed = distance/time)- units of m/s Velocity- speed and direction Acceleration- any chance in velocity (units are m/s^2) Mass- amount of matter in object, weight- force that acts upon an object **you are weightless in free fall!** Newton’s first law of motion- an object moves at constant velocity unless a net force acts to change its speed or direction (inertia) Newton’s second law of motion: force = mass x acceleration Newton’s third law of motion- for every force, there is always an equal and opposite reaction force Unbound orbits are not ellipses • What can make an object gain or lose orbital energy? Friction/atmospheric drag or gravitational encounter

• How does light interact with matter? Emission- sun, lamp; absorption, transmission, reflection/scattering (movie scatter light) • Wavelength x frequency = speed of light, c Order of frequencies- Gamma rays, x-rays, ultraviolet, visible, infrared, (microwaves), radio • 3 types of spectra: - emission line (close to ultraviolet) - continuous spectrum (around visible colors) - absorption line spectrum (close to infrared) • Properties of thermal radiation - hotter objects emit more light at all frequencies per unit area - hotter objects emit photons with a higher average energy Wien’s displacement law: max wavelength = 0.0029 (meters•kelvin)/ T (kelvin)→ wavelength is in nm Doppler effect- faster towards you = move towards blue, faster away from you = move towards red *speed is in km/s so you use c=3x10^5 km/s Over the course of a night, Polaris moves less than any other visible star in the sky. T As it moves in its orbit, Earth is always EXACTLY 1 AU from the Sun. False The seasons on Earth are caused by its elliptical orbit around the Sun. False It is possible to view the Moon in first-quarter phase the same day as a total lunar eclipse. False A solar eclipse can only occur when the Moon is new. True Copernicus’s Sun centered model of the solar system gave much better predictions than the Earth. False The celestial coordinates of the Sun change from day to day. True No matter where you live on Earth, the Sun is always directly overhead at noon. False There is no gravity in space. False Doubling the distance between two objects halves the gravitational force between them. False Grass is green because it absorbs green light, reflecting all other colors. False The shorter the wavelength of light, the higher its frequency. True X rays, because they have more energy, travel through space faster than visible light. F You are currently emitting electromagnetic waves in the infrared region of the electromagnetic spectrum. True Lines of a particular element appear at the same wavelength in both emission and absorption line spectra. True A radio telescope and an optical telescope of the same size have the same Diffraction Limit. False One light-hour is 1.08 billion km The precession cycle is 26,000 years You note that a particular star is directly overhead. It will be directly overhead again in 23 hrs and 56 min Given: The planet orbiting the nearby star 51 Pegasi is about 20X larger than the Earth and 400X more massive than Earth. The Earth has the following dimensions, M=5.98 x 1024 kg. And R=6.37x106m. Right here in your seat you are at a distance d = Rearth . Using Newton’s Law of Universal Gravitation determine your weight (Fg) on Earth. Once you do that, compare that answer to how much you would weigh on the planet orbiting 51 Pegasi. You would weigh the same as you do here To see the Sun’s hot outer layer at a temperature of 1,000,000 K, you should observe the x ray Ptolemaic model said the apparent retrograde motion of the planets by saying it held that the planets moved along small circles that moved on larger circles around Earth If we observe one edge of a star to be redshifted and the opposite edge to be blueshifted, we can conclude that the star is rotating It took two centuries for the Copernican model to replace the Ptolemaic model because there was no scientific evidence to support either model until Galileo made his observations If a material is highly opaque, then it absorbs most light All latitudes represent an extension of Earth’s equator onto the celestial sphere Atomic number=protons; atomic mass number=protons + neutrons Radiative energy= hxf; Precession does not change axis tilt Circumpolar: stars stay above the horizon Hotter stars are blue b/c blue is a shorter wavelength Eclipses can occur only when the phase of the Moon is full (for a lunar eclipse) or new (for a solar eclipse);the new/full moon occurs when the Moon is very close to a node...