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