Chapter 2: Discovering The Universe For Yourself Flashcards
Define celestial sphere
Sphere around earth where the stars and constellations lie
(Greeks)
(Wrong but still useful)
Define north celestial pole
Point directly over earth’s North Pole
Define south celestial pole
Point directly over earth’s South Pole
Define celestial equator
Projection of earth’s equator into space onto celestial sphere
Define ecliptic
Path sun follows as it appears to circle around the celestial sphere
Crosses celestial equator at 23.5 degree angle because earth is tilted
Define local sky
Sky seen from wherever you’re looking
Define zenith
Point directly above your head in local sky
Define horizon
Boundary between earth and sky
Define azimuth
Direction of an object clockwise from due north in degrees
How can we find the position of an object in the sky?
Azimuth in degrees, altitude
Define arcminutes
1/60 of a degree
‘ (ex 8 arcminutes = 8’)
Define arcseconds
1/60 arcminutes
“ (ex 8 arcseconds = 8”)
Define circumpolar
Stars near north celestial pole
Generally stay perpetually above the horizon, circling CCW around north celestial pole
Define latitude
Measures north to south position on earth
0 degrees at equator, 90 N at North Pole, 90 degrees at South Pole
Altitude of celestial pole in your sky = latitude
Define longitude
Measures east to west position on earth
0 along prime meridian, passes through Greenwich England
Define umbra
Where sunlight is completely blocked
Define penumbra
Where sunlight is only partially blocked
Define penumbral lunar eclipse
Moon only passes through earth’s penumbra
Define annular eclipse
Umbra of moon doesn’t reach earth, so ring of sunlight surrounds moon in small region of earth directly behind umbra
Saros cycle define
18 years, 11+1/3 days
Combination of changing dates of eclipse seasons and 29.5 day cycle of lunar phases
