AST101, Notes and Study Guide for Test 1
AST101, Notes and Study Guide for Test 1 AST101
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This 9 page Bundle was uploaded by Ali Ippolito on Monday February 22, 2016. The Bundle belongs to AST101 at Syracuse University taught by C. Armendariz-Picon in Spring 2016. Since its upload, it has received 2132 views. For similar materials see Our Corner of the Universe in Astronomy at Syracuse University.
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Date Created: 02/22/16
1 Section 1 Basic Information Lectures Lecture 1: Basic Course Information Lecture 2: The Celestial Sphere Lecture 3: The Motion of the Night Sky Lecture 4: The Motion of the Sun Lecture 5: The Motion of the Sun II Lecture 6: The Motion of the Planets Homework The Celestial Sphere (24 September 2015) The Motion of the Night Sky (24 September 2015) The Motion of the Planets (24 September 2015) The Motion of the Sun (24 September 2015) LectureTutorials Position Motion Seasonal Stars Solar vs. Sidereal Day Ecliptic Assessments Thursday, 24 September 2015 2 Lectures Lecture 1: Basic Course Information The Milky Way Dark spots because dust in the milky way that blocks the light from the stars behind it The Stars The stars appear to be points in the sky because they are far away from us o We can now take a telescope and analyze it, showing that it looks like our sun o Lights are just like our suns The Celestial Sphere Because stars are so far away, we cannot tell how far away they are It is then convenient to imagine that stars lie on a giant celestial sphere surrounding the earth We represent the sky with the celestial sphere The celestial sphere is actually very far away from the earth Another way to look at it: the “star theater” o Similar to what happens in a movie theater o The projector (the stars) is on the other side of the screen Constellations Stars appear to form patterns on the celestial sphere popularly known as constellations For astronomers constellations are regions of the celestial sphere o Regions are like countries on a map of a continent (different regions) Each point on the celestial sphere belongs to a particular constellation The starts in the same constellation can be very far from each other in actuality but appear to be close Celestial sphere Feature Earth at the center Straight line up from north pole north celestial pole (same with south) Celestial equator divides the sphere in half (projection of Earth’s equator in space) The Local Sky From our point of view, on earth, the sky looks like a dome Horizon: where the ground appears to end (and meets the celestial sphere) o Easier to see when looking at the ocean o The point beyond that you can’t see anything The meridian is a line that connects the north pole to south pole The North Star sits right on the Northern Celestial Pole Lecture 2: The Celestial Sphere Location On Earth Latitude is measured north or south of the equator Longitude is measured east or west of the prime meridian The prime meridian (longitude= 0 degrees), passes through Greenwich, England 3 Location, Location In order to specify your location on the earth, you need to know: o Latitude o Longitude Where are we? The altitude of the celestial pole above the horizon tells your latitude The local sky at the north pole (latitude 90 degrees North) “up” zenith latitude is distance from equator Like a circle in a spiral same as a clock clockwise vs. counterclockwise when you switch perception, the direction of the motion moves The night sky moves! We explain the motion of the night sky by assuming that the celestial sphere rotates clockwise around its axis (assuming that looking at the celestial sphere from the top, outside of it) Stars rise on the east and set on the west Because the sky rotates, the stars look like they follow a certain path (same motion as the celestial sky) Circumpolar (rotates around the pole) LectureTutorial: Position Lecture 3: The Motion of the Night Sky Last time The altitude of the celestial pole above the horizon is your latitude The celestial sphere rotates clockwise o Stars rise in the east and set in the east o Some stars are always visible o Some stars are visible only part of the time o Some stars are never visible Lecture: Motion A star is setting if it appears to go below the horizon, a star is rising if it appears to emerge from below the equator The Earth Spins The rotation of the celestial sphere is only a model In reality, stars remain essentially fixed as a day go by It is the earth that rotates once ever about 24 hours To explain the motion of the night sky, the earth must spin counterclockwise Here Comes the Sun The sun is also part of the sky, so its position can be represented on the celestial sphere 4 As any other star, the sun rises on the east and sets of the west as the celestial sphere (or the earth) spins once every 24 hours When the sun is above the horizon it is day time When the sun is below the horizon it is night time South is ahead of you and north is behind you at 12pm looking at the sun Not All Who Wander Are Lost As the year goes by, the sun appears to move counterclockwise on the celestial sphere along a path known as the ecliptic The constellations the ecliptic travels through are the Zodiacal constellations The ecliptic is at an angel of 23.5 degrees Lecture 4 and 5: The Motion of the Sun Last time The sun on the celestial sphere Two simultaneous motions o Celestial sphere rotates once a day The sun, and any other stars, rises east and sets west o The sun moves along the ecliptic once a year The sun appears to drift eastward along the Zodiacal constellations Location on the Celestial Sphere Ecliptic o Summer solstice June 21 (the point at which the sun can’t go farther north) st o Autumnal (fall) equinox September 21 Sun rises exactly due east Daytime and nighttime are equally long o Winter solstice December 21 st nd o Vernal (spring) equinox March 22 Tell It the Way It is The sun is not like a ladybug stuck to the celestial sphere In reality, the apparent motion of the sun along the ecliptic is due to the earth’s orbit around the sun The difference between ecliptic and celestial equator is due to the tilt of the earth’s rotational axis To explain the counterclockwise motion of the sun along the ecliptic, the earth must orbit the sun counterclockwise Lecture 6: The Motion of the Planets Last time Seasonal changes in the location of the sun o Solstices o Equinoxes The earth orbits around the sun Sidereal day Time it takes for the stars to complete one cycle through the sky Time it takes for the planet to rotate 360 degrees (to complete one cycle) 5 After one sidereal day, the star will return to the exact spot as before earth must be pointed in the same direction Related to the location of the stars 23 hours and 56 minutes Solar Day Time it takes the sun to return to its highest location on earth on the sky 24 hours on earth On earth, a solar day is longer than a sidereal day These wandering “stars” are actually solar system planets Mars November through June it usually moves eastward relative to the stars Strange: reverses course during its apparent retrograde motion (July 30September 29 th Celestial sphere model fails with this because can’t explain the motion of planets The Ptolemaic Model Earth is at the center and planets rotate around epicycle Planets are stuck to the epicycle Abandoned after Galileo Sun Centered Model Inner planets go faster than the outer planets 6 Homework The Celestial Sphere Two stars that are in the same constellation: May actually be very far away from each other What do astronomers mean by a constellation? A constellation is a region in the sky as seen from earth What is the celestial sphere? The celestial sphere is a representation of how the entire sky looks as seen from Earth What do we mean when we talk about the Milky Way in our sky? The patchy band of light that outlines the plane of the Milky Way Galaxy as seen from Earth Which of the following correctly describes the meridian in your local sky? A halfcircle extending from your horizon due north through your zenith, to your horizon due south The point directly over your head is called… The zenith The Motion of the Night Sky Stars that are visible in the local sky on any clear night of the year, at any time of the night, are called… Circumpolar If you are located in the Northern Hemisphere, which of the following correctly describes a relationship between the sky and your location? The altitude of the north celestial pole equals your latitude The North Celestial Pole is 35 degrees above your northern horizon. This tells you that… You are at latitude, 35 degrees north Beijing and Philadelphia have about the same latitude but very different longitudes. Therefore, tonight's night sky in these two places: will look about the same Suppose that you are in Miami, Florida and look at the sky. What are your longitude and latitude? The latitude in Miami is 26 degrees north and the longitude is 117 degrees west. Suppose that you are in Miami, Florida and look at the sky. Where does the north (or south) celestial pole appear in your sky? The north celestial pole appears in Miami 's sky at an altitude of 26 degrees in the direction due north Is Polaris a circumpolar star in Miami 's sky? Choose the correct explanation. Polaris is circumpolar because it never rises or sets in Miami 's sky Which of the following statements about the celestial sphere is not true? The "celestial sphere" is another name for our universe 7 When traveling north from the United States into Canada, you'll see the North Star (Polaris) getting… Higher in the sky Suppose you use the Southern Cross to determine that the south celestial pole appears 40 degrees above your horizon. Then you must be located at… latitude 40 degrees south Suppose you are facing north and you see the Big Dipper close to your northern horizon, with Polaris (and the Little Dipper) above it. Where will you see the Big Dipper in six hours? to the right of Polaris; that is, 90 degrees counterclockwise from its current position RXJ1800, a galaxy, lies very near in the sky to the bright star Vega. What is the best explanation for them appearing close together? They coincidentally lie along the same line of sight What do astronomers mean by a constellation? A constellation is a region in the sky as seen from Earth Stars that are visible in the local sky on any clear night of the year, at any time of the night, are called… Circumpolar We describe a location on Earth's surface by stating its… Latitude and longitude If you are located in the Northern Hemisphere, which of the following correctly describes a relationship between the sky and your location? The altitude of the north celestial pole equals your latitude What is a circumpolar star? a star that always remains above your horizon What makes the North Star, Polaris, special? It appears very near the north celestial pole Which of the following statements about circumpolar stars is true at all latitudes? They always remain above your horizon You are standing on Earth's equator. Which way is Polaris, the North star? on the northern horizon By locating the north celestial pole (NCP) in the sky, how can you determine your latitude? The altitude of the NCP is the same as your latitude The Motion of the Planets In the demonstration, 360 degrees of rotation (one full rotation) represents a sidereal day. You can actually measure the length of the sidereal day by measuring the time from when __________ crosses your meridian on one day (or night) until it crosses the meridian on the next day (or night). The star Vega The star Sirius 8 As shown in the figure, a solar day requires about an extra 1° of rotation, or a total of about 361° of rotation for Earth. Therefore, a solar day is longer than a sidereal day by about… 1/360 of 24 hours Which of the following changes would cause the solar day to be shorter (rather than longer) than the sidereal day? Reversing the direction of Earth's rotation Suppose that Earth orbited the Sun 10 times as fast as it actually does but kept the same rotation period it has now. Which of the following would be true? The sidereal day would still be 23 hours, 56 minutes, but the solar day would be a little over 24 1/2 hours The Moon takes about 1 month to orbit Earth (more precisely, about 27 1/3 days), and it travels in the same direction that Earth orbits the Sun. Therefore, during the time it takes the Moon to complete one orbit around Earth, Earth moves __________ around its orbit of the Sun. about 1/12 of the way Based on your answer to Part E, the time from one new moon to the next must be _________. longer than the Moon's actual orbital period by about 1/12 of the 27day orbital period During the time that a planet is in its period of apparent retrograde motion… over many days or weeks, the planet moves westward relative to the stars, rather than the usual eastward relative to the stars When we see Saturn going through a period of apparent retrograde motion, it means… Earth is passing Saturn in its orbit, with both planets on the same side of the Sun At most times, Mars appears to move __________ relative to the stars. The exceptions are during its periods of apparent retrograde motion, when Mars appears to move __________ relative to the stars. To the left (eastward); to the left (eastward) If you wanted to document the apparent retrograde motion of Mars, you would need to measure and record Mars's __________ over a period of __________. Position among the constellations; several months What is really happening in space during the periods when we see Mars going through apparent retrograde motion? Earth is passing by Mars in its orbit around the Sun Consider a time when Mars is in the middle of one of its periods of apparent retrograde motion. During this time, Mars appears _____ in our night sky and crosses the meridian around _____. Brightest; midnight The Suncentered system pictured in the lower window of the animation offers a simple explanation for observations of apparent retrograde motion. Should these facts alone have been enough to convince the ancient Greeks that Earth really does go around the Sun? No, because the Greeks had an Earthcentered model that also accounted for apparent retrograde motion 9 During the period each year when we see Mars undergoing apparent retrograde motion in our sky, what is really going on in space? Earth is catching up with and passing by Mars in their respective orbits What happens during the apparent retrograde motion of a planet? The planet appears to move westward with respect to the stars over a period of many nights What causes the apparent retrograde motion of the planets? As Earth passes another planet, the other planet appears to move backward with respect to the background stars, but the planet's motion does not really change Which of the following never goes in retrograde motion? The Sun The Motion of the Sun What is the ecliptic? the path the Sun appears to trace around the celestial sphere each year In any particular place on Earth, certain constellations are visible in the evening only at certain times of the year because… our evening view of space depends on where Earth is located in its orbit around the Sun The Sun's path, as viewed from the equator, is highest in the sky on… the spring and fall equinoxes Suppose Earth's axis tilt was significantly greater than its current 23.5 degrees, but Earth's rotation period and orbital period were unchanged. Which statement below would not be true? The length of each season (for example, the number of days from the summer solstice to the fall equinox) would be significantly longer than it is now If our year were twice as long (that is, if Earth took twice as many days to complete each orbit around the Sun), but Earth's rotation period and axis tilt were unchanged, then… the four seasons would each be twice as long as they are now You are standing on Earth's equator. Which way is Polaris, the North star? on the northern horizon Orion is visible on winter evenings but not summer evenings because of the location of Earth in its orbit
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