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Week 3--Lecture 4

by: Caitlin Acierno

Week 3--Lecture 4 Astronomy 104

Caitlin Acierno
GPA 3.0

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These notes are from lecture 4
Exploration of the Solar System
Jim Lattis
Class Notes
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This 2 page Class Notes was uploaded by Caitlin Acierno on Saturday February 6, 2016. The Class Notes belongs to Astronomy 104 at University of Wisconsin - Madison taught by Jim Lattis in Spring 2016. Since its upload, it has received 23 views.


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Date Created: 02/06/16
Plane of ecliptic Plane or Moon’s orbit—5 degrees tipped Intersection: Lines of Nodes Ascending node, descending node  Crossing points where the two lines intersect and the Moon’s orbit passes through.  Most full moons and new moons don’t result in eclipses because of this? Phase measures only the angle away from Earth-Sun line At angles of 0 degrees and 180 degrees, you have “syzygy”  Term sometimes also applied to alignments of Sun, Earth, and a planet  North-South motion of Moon, i.e. the inclination of the plane of the lunar orbit wrt Earth’s orbit (ecliptic) is needed to understand… Orbital inclination adds North-South motion. Tilt ~5 degrees New moon near node  Possible solar eclipse Full moon near node  Possible lunar eclipse Lunar orbit “Precesses,” i.e. nodes move westward: “regression of the nodes”  So “eclipse seasons” do not happen every 6 months but come a few days earlier each cycle  Nodes complete rotation in ~18 2/3 years  360 degrees/18.7 years = ~19 degrees/year  Or ~20 days/year = 10 days earlier each “season”  3x18 2/3 years = 56 years, so lunar eclipse patterns repeat pretty close to every 56 years. Stonehenge (Aubrey Holes)  56 “holes” might have marked events in lunar eclipse cycles Galileo, 1609  “Ashen Light” o Also called “earthshine,” “old moon in new moon’s arms” o Sunlight, twice reflected o Nearly new Moon means nearly full Earth More Coordinates: Equatorial  Rotation of Earth: West to East o California follows New York  Counter-clockwise as viewed from above North Pole o “right hand” rule  Consider Mintaka, in Orion o Rises due East, sets due West o Traces celestial equator o Question: Where on Earth would you see it at the zenith? Equatorial Coordinates  90 degrees north and south of celestial equator o North celestial pole (NCP) o South Celestial Pole (SCP)  Celestial objects ascend daily in the east and descend in the west, paths centered on celestial poles  If path crosses horizon, object will rise and set  If close enough to the pose, it’s circumpolar. Review Motions of the Sun  Annual solar motion o Earth orbits ccw viewed from North o Sun appears to shift eastward wrt stars o Sun’s eastward motion makes sidereal day 4 minutes shorter than solar day o Sun’s apparent annual motion (eastward) is opposite to apparent diurnal motion (westward) of stars. Lunar Eclipses  Inclination of lunar orbit to ecliptic  Don’t get one every full moon because it is not commonly at one of the nodes.  Must occur at full moon  Visible across the entire hemisphere, so more common in our experience than solar eclipses  Umbra; penumbra  Moon can be reddish in umbra  Fun, nearly effortless to watch  No longer scientifically important. o Used to be one of the few ways for astronomers to measure longitude on the earth.


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