Astronomy 154L

Horizon

Great circle on the celestial sphere of which zenith and nadir are the poles. In other words, great circle which is halfway 90 degrees from both zenith and nadir.

imaginary sphere of a very large radius,centered on the earth; the apparent sphere of the sky

celestial sphere

circle on a sphere whose center is located in the center of the sphere

great circle

Zenith

Point on the celestial sphere opposite to the direction of gravity

Turning of a body about an axis running through it

rotation

right ascension

(astronomy) the angular distance eastward along the celestial equator from the vernal equinox to the intersection of the hour circle that passes through the body

vernal equinox

(astronomy) the equinoctial point that lies in the constellation of Pisces

declination

A measure of how far north or south an object is from the celestial equator

hour angle

Angle measured eastward (-) or westward (+) between the observers meridian and the hour circle of the celestial object. It is expressed in hrs, min, and sec of time

hour circle

Astronomical meridian or the semi circle on the celestial sphere whose end points are located at the celestial pole

winter solstice

December 22, when the sun is at its southernmost point

longitude

E or West North and South Green Which Meridian 0 longitude 24 lines north and south poles

summer solstice

June 21, when the sun is at its northernmost point

autumnal equinox

Occurs on or about September 22 when all parts of the Earth receive 12 hours of

ecliptic

Path of the sun and the planets

azimuth

The angular distance along the horizon measured clockwise from the north toward perpendicular to the horizon.

greenwich meridian

The line of zero degrees longitude which passes through Greenwich England. All of the longitudes are measured from this line.

Latitude

They are measured in North or South degrees. East to west North Pole 90 degrees North latitude and south pole 90 degrees south latitude parallel

celestial equator

a great circle on the celestial sphere 90 degrees from the celestial poles. It divides the celestial sphere into northern and southern hemispheres.

obliquity of ecliptic

angle of 23.5 degrees of earths rotation

altitude

angular distance of a celestial object above or below the horizon measured along a vertical circle passing through the object.

vertical circle

any great circle passing through the observers zenith.

direction of the earths rotation

east direction

north point

intersection of the meridian and horizon which is directly underneath the north celestial pole.

Nadir

opposite point from the zenith on the celestial sphere

the axis of Earth's rotation

polar axis

the orbital motion of one body around another

revolution

meridian

the great circle on the celestial sphere that passes thru the north and south celestial poles and the observers zenith.

celestial poles

the points on the celestial sphere that are directly overhead at the earth's poles

direction opposite to the earth's rotation

west direction