Astronomy Section 2
Astronomy Section 2 ASTRO103
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This 62 page Bundle was uploaded by Morgan Oestmann on Wednesday May 4, 2016. The Bundle belongs to ASTRO103 at University of Nebraska Lincoln taught by Michael Sibbernsen in Spring 2016. Since its upload, it has received 19 views. For similar materials see Introductory Astronomy in Astronomy at University of Nebraska Lincoln.
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Date Created: 05/04/16
Coordinate Systems I: Lecture Outline Terrestrial Coordinates o Longitude o Latitude o Named Coordinate Features Celestial Equatorial Coordinates o Declination o Right Ascension o Named Coordinate Features o Precession of the Equinoxes Terrestrial Coordinate System Longitude o Tells where one is East or west o Lines are “great circles” o Goes from 0 to 180E and 0 to 180W o 0 line is Prime Meridian o 180 line is the International Date Line Latitude o Tells where one is North and South o Circles of varying sizes o Equator is the largest of the “parallels of latitude” Celestial Equatorial Coordinates Polaris o North Star o Very near the North Celestial Pole Right Ascension o O-24 hours o Each “hour” is subdivided into 60 minutes o 0h=24h is at the Vernal Equinox Point Declination o +90 to -90 o North Celstial Pole is +90 o South Celestial Pole is -90 o Celestial Equator is 0 Ecliptic-apparent path of the sun in the sky Coordinate Systems II: Motion of Earth Outline Rotation of Earth on its axis Revolution of Earth in its orbit Sidereal and Synodic Ecliptic Obliquity o Intensity of Light Rays o Seasons Ecliptic Plane of the earth’s orbit around the sun Revolution Revolution of Earth makes the sun appear to move eastward O along the ecliptic about 1 /day Sidereal and Synodic Combining Rotation and Revolution o Sidereal Day= 23 hours, 56 minutes o Solar Day= 24 hours o Stars rise and set 4 min earlier every day Obliquity o Degree between the equator and the plane of earth’s o Seasons are caused by Obliquity—not changing distance from the sun Oblique light rays are less intense (winter) Seasons and the Ecliptic Coordinate Systems II: Motion of Earth Outline Rotation of Earth on its axis Revolution of Earth in its orbit Sidereal and Synodic Ecliptic Obliquity o Intensity of Light Rays o Seasons Ecliptic Plane of the earth’s orbit around the sun Revolution Revolution of Earth makes the sun appear to move eastward O along the ecliptic about 1 /day Sidereal and Synodic Combining Rotation and Revolution o Sidereal Day= 23 hours, 56 minutes o Solar Day= 24 hours o Stars rise and set 4 min earlier every day Obliquity o Degree between the equator and the plane of earth’s o Seasons are caused by Obliquity—not changing distance from the sun Oblique light rays are less intense (winter) Seasons and the Ecliptic Coordinate Systems III: The Horizon Coordinate System Horizon Coordinate System o Relationship to position on the earth and sky o Coordinate name and units, named features Relating Horizon Coordinates to Celestial Spheres Coordinates Meridional Altitude Finding Meridional Altitude Every observer only sees half of the sky/celestial sphere at any one time The Astronomical Horizon is the plane tangent to the surface of the earth Zenith—directly above Nadir—Directly below Finding an Horizon Coordinate o Step 1—note the vertical circle of the object and get azimuth o Step 2—note the altitude of the object Relating Horizon to Celestial Coordinates Step 1—Note that altitude of the North Celestial Pole is equal to the latitude of the observer Every observer sees one celestial pole in their sky. Observers in the northern hemisphere see the NCP above the north point— observes in the southern hemisphere the SCP above the south point of their horizon. Both see the pole at altitudes equal to their latitudes Relating Horizon to Celstial Coordinates Step 1—altitude of NCP=latitude Step 2—maximum altitude of celestial equator is 90 latitude Meridional Altitude Point where star crosses the meridian o “Highest” the star will be in the observer’s sky o Azimuth is 180 (or 0”) Given by altitude of the celestial equator and the clination of the star Coordinate Systems IV Applications of Horizon Diagrams o Paths of the Sun o Declination Ranges o Star Trails o Locations of the Planets, sun, and moon Declination Ranges o 3 types of Stars Circumpolar Rise and Set Never Rise o General Rules Circumpolar Range—from (90-latitude) to the pole (90) in the hemisphere of the observer Never Rise—a symmetric region to the Circumpolar Range from (90-lat) to the pole of the other hemisphere Rise and Set—everything that’s left—the 3 ranges must add up to 180—from (90-latitude) in one hemisphere to (90-lat) in the other Lunar Phases Lecture Summary Lunar Orbit o Inclination Periods o Synodic and Sidereal Phases o Geometric Cause o Rising, Meridional, and Setting Times o Horizon Diagrams Scale and Size of the Moon The moon’s diameter is 1/4 of the earth’s Moon is about 30 earth diameter’s away Distance o Mean=384,000 km o Perigee (closest the moon is earth)= 363.100 KM o Apogee (Furthest the moon is from earth)= 405,700 KM Eccentricity o e=0.055 Angular Diameter of the Moon 0 Same angular diameter of .5 Looks larger at Perigee Inclination Lunar Periods Sidereal o With respect to the stars o 27.3 days Synodic o With respect to the sun o 29.5 days Lunar Rotation Does the moon rotate? o Yes—with a period of rotation equal to its period of revolution o Synchronic Rotations Librations Over time, we can photograph 59% of the moon from Earth Phases of the Moon Lunar Tides and Eclipses Summary Tides o Differential gravity o Spring o Neap Eclipses o Lunar o Solar Tides—Caused by Gravity Caused by the moon’s (differential) gravity FGravityGMm/R ) 2 Spring and Neap Tides Spring Tides: sun and moon aligned Neap Tides: sun and moon at right angles Tides and the Earth’s Rotation Eclipses Solar—Earth, Moon, Sun o Total Solar Eclipse Moon completely obscures the sun (observer standing in the umbra) o Partial Solar Eclipse Moon partially obscures the sun (observer standing in the penumbra) o Annular Solar Eclipse Moon’s angular diameter smaller than the suns—a ring of the sun surrounds the moon Lunar—Moon, Earth, Sun o Total Lunar Eclipse Moon entirely inside earth’s umbra o Partial Lunar Eclipse Moon is partially inside earth’s umbra o Penumbral Lunar Eclipse Moon inside penumbra only Types of Shadow Umbra—region of total shadow Penumbra—region of partial shadow Inclination of Moon’s Orbit Saros Cycle Every 18 years 11 and 1/3 days the same configuration for an eclipe reoccurs Because of the 1/3 day, that eclipse will occur 1/3 of the way around the earth Eclipse will come back to the same spot about every 54 years, 34 days
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