AST 1002 Lecture Notes - Lecture 2: Orbital Speed, Geocentric Model, Copernican Revolution
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Earth is a sphere at the center of the universe. Celestial motions are (cid:272)o(cid:374)sta(cid:374)t a(cid:374)d (cid:272)i(cid:396)(cid:272)ula(cid:396) o(cid:396)(cid:271)iti(cid:374)g ea(cid:396)th o(cid:374)(cid:272)e pe(cid:396) da(cid:455). The moon, planets, and stars all reside on spheres that circle the earth. P(cid:396)efe(cid:396)(cid:396)ed the geo(cid:272)e(cid:374)t(cid:396)i(cid:272) (cid:373)odel (cid:271)e(cid:272)ause sta(cid:396)s did(cid:374)"t sho(cid:449) a(cid:374)(cid:455) pa(cid:396)alla(cid:454), (cid:449)e do(cid:374)"t feel as though ea(cid:396)th (cid:373)o(cid:448)es, o(cid:271)je(cid:272)ts fall to(cid:449)a(cid:396)d ea(cid:396)th, (cid:374)ot the u(cid:374), a(cid:374)d (cid:449)e do(cid:374)"t feel a(cid:374)d e(cid:374)o(cid:396)(cid:373)ous (cid:449)i(cid:374) due to ea(cid:396)th"s (cid:373)otio(cid:374). Hipparchus (150 bc): if earth was going around the sun, there should be parallax. Problem #2: venus and mercury are never far from the sun in the sky. Explain problems with deferents (orbit) and epicycles (orbit within orbit) Planets have epicycles, sun and moon do not. Copernican revolution: earth spins like a top, once per day. No parallax because stars are much farther away than the sun and planets. Natu(cid:396)al e(cid:454)pla(cid:374)atio(cid:374) fo(cid:396) (cid:396)et(cid:396)og(cid:396)ade (cid:373)otio(cid:374) (cid:894)i(cid:374)(cid:374)e(cid:396) pla(cid:374)ets o(cid:396)(cid:271)it faster)
