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Week 1 and 2--Lectures 2*-3

by: Caitlin Acierno

Week 1 and 2--Lectures 2*-3 Astronomy 104

Caitlin Acierno
GPA 3.0
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These notes are from lectures on January 25 and 27. *We did not get to any lecture time in class on January 20.
Exploration of the Solar System
Jim Lattis
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This 5 page Class Notes was uploaded by Caitlin Acierno on Friday January 29, 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 26 views.


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Date Created: 01/29/16
January’s Sky  Stellarium o Can explore the sky where you are  Constellations  Moon  Planets, evening o Jupiter If the entire solar system was about 1 cm wide, the next star system would be 200 feet away. How big would the galaxy be? 1000 miles in diameter. A Sense of Scale  Astronomical Unit: o The estimated distance the Earth is from the sun o Pluto is about 40 AU out o Voyager 2 is about 100 AU out New Planet? “Planet Nine”  What is a “planet?” o A big thing, not a star, orbiting the star  How Big? o This is a problem o Big enough to run with the big dogs  Minor Bodies o Comets o Asteroids o Kuiper Belt objects  Around where Pluto is  The idea is that Planet X is out there and is so large that it is influencing the orbits of the other possible planets found out beyond Pluto. o Mike Brown (?) does research on this. “Planet Nine”?  Mass o ~Neptune, ~17M Earth  Orbit o Period: 10-20,000 years o Perihelion ~200 AU o Aphelion ~1200 AU o ?  Confirmation? o Search with big telescopes o Maybe already imaged How Science (often) works  Study objects, look for regularities, find some  Make hypothesis about what’s happening  Apply theory to make predictions  Try to confirm hypothesis or predictions  If confirmed, Nobel Prize (maybe)  If not confirmed o Recheck those regularities o Try a new hypothesis  Evidence, when you can get it, decides the questions. Sidereal Motions (Motions of the Stars)  Go to Stellarium Why does a star transit the meridian 4 minutes earlier each day?  Because of the eccentricity of Earth’s orbit. Precessional motion  Caesar? Why is summer warmer than winter?  The change in the elevation of the sun in the sky  The seasons are poorly understood, despite their familiarity o Recommended video: My Private Universe  Common misconception: seasons caused by varying distance between Sun and Earth o Seasons in N and S hemispheres not simultaneous  Date of aphelion ~4 July; perihelion ~3 January o Distance effect (not measurable in antiquity)  Aphelion distance ~152,097,000 km  Perihelion distance ~147,094,000 km  Seasons caused by tilt of ecliptic wrt equator o Define  Equator  Ecliptic o June and December solstices  Extreme lengths of daylight and darkness o March and September equinoxes  Equality of daylight and darkness Phases of the Moon  …  Crescent moon o From latin “crescere” to grow o Cap ital “crescendo o Difficult to find until a couple of days after new  First quarter o 90 degrees east of sun o Rises around noon o Transits meridian around sunset o Sets around midnight (notice “straight” back)  Waxing gibbous o “hump-back” rather than straight-back o Now lower in the east each day at sunset o Rounder on the western side (“Gobba a ponente…”)  Full moon o Rises at sunset o Transits local meridian at midnight o Sets at sunrise o High in sky in winter o Low in sky in summer  Waning gibbous o Rising later after sunset each day o Hump-back diminishing o Rounder on the easter side (“Gobba a levanter…”)  Last (“waning”) quarter o 90 degrees west of sun o Rises…  Waning cresecnet o Return to vicinity of sun o Lower in the dawn each morning o Oxymoron o Recurrence of new moon cycle Causes of Lunar Phases  Why do we see the lunar phases? o Our viewing angle changes as the moon orbits eather  …? Lunar Motions  360 decgrees in ~30 days => ~12 degrees a day  Moon’s apparent dameter: ~1/2 degrees  ~12 degrees/24 hours = ~1/2 degree per hour o i.e. moon moves through the starts at a distance roughtly equal to its own diameter each hour!  This is the moon’s proper motion o As distinguished from, e.g. its diurnal motion  Easily detectable by naked eye


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