1	Astr 1050 Mon. Jan. 26, 2004 Powers of ten on the web: http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html Finish chapter 2 topics Magnitude Scale The Celestial Sphere Start chapter 3: Cycles in the Sky
2	Apparent Visual Magnitude Scale From our Text, Horizons by Seeds
3	Formula for Intensity vs. m:
4	Examples:
5	Examples:
6	Examples:
7	Examples:
8	The View From A Rotating Platform Imagine being in a rotating restaurant on top of a tall building. All the outside objects are very far away – much farther than the distance across the room. Paint the view on the windows – and keep the people near the center of the room – away from the windows themselves. Can the people tell if the room is rotating, or if the painted windows are just moving around the room? Which is more reasonable – a rotating room or rotating painted windows?
9	Celestial Sphere
10	Nomenclature HORIZON: The horizontal circle which separates the part of the sky visible to you and the part of the sky hidden by the earth. ZENITH: The point on the sky directly overhead. MERIDIAN: The circle which starts on the northern horizon, runs through the zenith, continuing on to the southern horizon. It separates the eastern half of the sky from the western half. CELESTIAL POLES: The points where the extension of the rotation axis of the earth would intersect the celestial sphere. CELESTIAL EQUATOR: The circle around the sky which would be a projection of the earth’s equator.
11	Limiting Cases At the Earth’s north pole, looking overhead all stars appear to circle around the north celestial pole. At the equator: Stars on the celestial equator rise in the east, move overhead, then set in the west The N and S celestial poles are just on your N and S horizons, and stars near those points still circle around them. But those stars are only visible for the upper half of their circles.
12	Intermediate cases like Laramie Stars close enough to the north celestial pole are always above the horizon, and just circle the pole star. (CIRCUMPOLAR STARS) Stars on the celestial equator rise in the east, move higher along a slanted path which crosses the “meridian” to the south of the zenith, then descend and set due west. Stars far enough to the south never make it above the horizon.
13	Star Motion from the Northern Hemisphere
14	Precession of the Earth The earth’s axis of rotation is tilted 23.5⁰ relative to the plane containing the sun and other planets. The gravity from the Sun and moon is trying to tip the earth just like gravity is trying to tip a spinning top. As with the top, the axis of the earth wobbles or PRECESSES in space, with a 26,000 year period. Because the directions to the celestial poles are defined by the spin axis – those poles move with time. It isn’t that the stars move – it is that the grid we paint on the celestial sphere has to be redrawn from time-to-time. Eventually Polaris will not be the “pole” star.
15	Start Chapter 3: Cycles in the Sky Motion of the Sun through the year Plot position of Sun relative to stars, over one full year. Complicated by fact you can’t see Sun and stars at same time. Once you have full map of sky, you can work this out by seeing what stars are opposite sun 12 hours later.
16	Plotting the Ecliptic on the Celestial Sphere
17	Consider the Sun’s daily motion thru the year
18	How the Sun’s location affects the seasons:
19	Special Locations on the Earth
20	Why are the planets found near the ecliptic?
21	Superior vs. Inferior Planets
22	Inferior Planets
23	Effect of Elliptical Orbit on Climate Seasons almost entirely due to TILT of Earth Seasons opposite (not the same) in N & S Hemispheres Earth’s orbit slightly elliptical Slightly closer to the sun in N. Hemisphere Winter But this changes as tilt precesses in 26,000 yr cycle Expect N. Hemisphere winter to be slightly milder Positions of continents and oceans actually more important Effect is important for Mars -- more elliptical orbit Cyclic variations in climate as tilt precesses (and tilt and ellipticity also gets slightly larger and smaller VERY IMPORTANT TOPIC (Re: Global Warming)
24	For Wednesday: