ASTR 152 Lecture Notes - Lecture 4: Ptolemy, Retrograde And Prograde Motion, Nicolaus Copernicus
Document Summary
Chapter 4: planets, planetary motion, and laws that govern motion. Planets are visible in our nighttime sky because they are illuminated by reflected sunlight; they do(cid:374)"t p(cid:396)odu(cid:272)e thei(cid:396) o(cid:449)(cid:374) light. Five planets appear bright enough to be seen by the naked eye (mercury, venus, mars, jupiter, and. All pla(cid:374)ets u(cid:374)de(cid:396)go (cid:862)daily (cid:373)otio(cid:374)(cid:863) a(cid:272)(cid:396)oss the sky, f(cid:396)o(cid:373) east to west (cid:894)just like sta(cid:396)s(cid:895), a(cid:374)d thei(cid:396) daily (cid:373)otio(cid:374) is also due to the ea(cid:396)th"s (cid:396)otatio(cid:374). How do we distinguish planets from stars: 1. Their light is steady, while light from stars twinkle/shimmer: 2. As all planets revolve around the sun, from west to east, they move slowly among fixed background stars; their motion is near the ecliptic. Eastern elongations pla(cid:374)ets a(cid:396)e see(cid:374) as (cid:862)e(cid:448)e(cid:374)i(cid:374)g pla(cid:374)ets(cid:863) Opposition planets are visible all night; retrograde motion occurs. Western elongation pla(cid:374)ets a(cid:396)e see(cid:374) as (cid:862)mo(cid:396)(cid:374)i(cid:374)g pla(cid:374)ets(cid:863) Why does (cid:862)(cid:396)et(cid:396)og(cid:396)ade(cid:863) (cid:373)otio(cid:374) happe(cid:374): earth travels in its orbit and overtakes the other planet near or at opposition.
