Chapter 2 Flashcards
(33 cards)
direction stars appear to move in the night sky
counterclockwise, E → W
number of constellations
88
etymology of “constellation”
“group of stars”
positional astronomy
the study of the positions of objects in the sky and how these positions change
diurnal motion
daily motion of stars across the sky
celestial equator
Earths’ equator projected onto the celestial sphere
celestial poles
Earth’s north and south pole projected onto the celestial sphere
zenith
the point in the sky directly overhead an observer/ a location
circumpolar stars
stars which revolve around the celestial pole throughout the day instead of rising/setting
Dependent on latitude
Earth’s tilt
23.5 degrees
declination
angular distance north or south of the celestial equator
right assention
the angular distance from the vernal equinox eastward along the celestial equator to the circle used in measuring its declination
measured in time required for the celestial sphere to rotate through this angle
vernal equinox
one of two points where the sun crosses the celestial equator during its apparent annual motion
ecliptic plane
the plane of the Earth’s motion around the sun
ecliptic
path the sun appears to trace out over a year on the celestial sphere
equinox
intersection of the celestial equator and ecliptic
vernal (beginning of spring in North Hemisphere) and autumnal (beginning of autumn in North Hemisphere)
tropic of cancer (N) and tropic of capricorn (S)
23.5 degrees N/S of the equator
between these lines, the sun passes over the zenith at least once per year
zodiac
the band around the ecliptic which contains the moon’s path
about 8 degrees from the ecliptic
procession
the change in orientation of Earth’s rotational axis due to the sun and moon’s gravitational pull on the Earth’s equatorial “bulge”
known as the “procession of the equinoxes
length of processional cycle
26,000 years
term for the date in astronomy
epoch
Sundial
measures apparent solar time
meridian
a North/South circle on the celestial sphere which passes through the zenith
defines local noon and local midnight
meridian transit
the crossing of the meridian by any object in the sky
