Astronomy Terms

Terrestial/Celestial Equator

The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space. As a result of the Earth's axial tilt, the celestial equator is inclined by 23.4° with respect to the ecliptic plan

Celestial horizon

The celestial horizon is the great circle located 90 degrees from the zenith. It divides the celestial sphere into an upper (visible) half , and a lower (not visible) half. The only times we are likely to see the celestial horizon are when we are at sea or in the middle of a vast plain.

Celestial Equator

The circle where the Earth's equator, if extended outward into space, would intersect the celestial sphere.

Circumpolar Stars

The circumpolar stars never set but move on circles centered near Polaris.

Direct Motion

The eastward apparent motion of a solar system body with respect to the stars. Direct motion is uninterrupted by regular episodes of retrograde motion

Prime Meridian

The longitude line passing through Greenwich is called the prime meridian (A.K.A Greenwich meridian)

Degree measure (using finger)

The most commonly used system for measuring angles uses degrees. A degree is 1⁄360 of a circle.

Ecliptic

The path that the sun follows among the stars. . The angle between the equator and the ecliptic is 23.5 The plane of the Earth's orbit about the Sun. As a result of the Earth's motion, the Sun appears to move among the stars, following a path

Autumnal Equinox

The point in the sky where the Sun appears to cross the celestial equator moving north to south. This happens on approximtely September 22

Vernal (spring) Equinox

The point in the sky where the sun appears to cross the celestial equator moving from south to north. This happens approximately on March 21

Zenith

The point on the celestial spher e directly over your head.

Summer Solstice

The point on the ecliptic where the Sun's declination is most nothely. The time when the sun is at the summer solstice, around June 21, marks the beginning of summer

Winter Solstice

The point on the ecliptic where the sun has the most southernly declination. The time when the sun is at the winter solstice, around December 22, marks the beginning of winter

Milky Way

The spiral galaxy containing our solar system.

Retrograde Motion

The westward revolution of a solar system body around the sun -> only planets do that

Apparent Solar Time

Time as calculated according to the actual position of the sun in the sky. Occurs when the sun crosses an observer's meridian.

Winter Solstice Equinox Summer Solstice Vernal Spring

W- 12 Sp- 3 Su- 6 Fall- 9

Great Circle

a circle that divides a sphere into two equal parts. The equator divides the Earth into northern and southern hemispheres.

Second/Minute of arc

a unit of angular measurement equal to 1/60 of one degree.

am/pm

am- anti meridian pm-

converting degrees to sexigsmal

bih what

Planet

A celestial body moving in an elliptical orbit around a star. in orbit around the Sun. Greek word for wanderer

Horizon System

A coordinate system, using altitude and azimuth as coordinates, used to locate the positions of objects in the sky.

Constellations

A grouping of stars on the celestial sphere that appear to be located close together in the sky and that form a picture if lines connecting them are imagined.

Star

A massive gaseous body that has used, is using, or will use nuclear fusion to produce the bulk of the energy it radiates into space

Altitude

Altitude is the angular distance above the celestial horizon and corresponds to latitude in the terrestrial coordinate system. Altitude is the angle measured upward from the horizon. (horizon has an altitude of 0, zenith has an altitude of 90)

Right Ascension

Angular distance of a body along the celestial equator from the vernal equinox eastward to the point on the equator nearest the body. Right ascension is analogous to longitude in the terrestrial coordinate system

Azimuth

Azimuth is the angle measured eastward around the horizon from north. Azimuth is the angular distance measured from north eastward around the celestial horizon to the point directly below the chosen location on the celestial sphere. Azimuth corresponds to longitude in the terrestrial coordinate system.

Equinox literally means

Equal-Night

Declination

How far it is from the celestial equator

Latitude

Latitude is the angle between the equator and a geographical location.

Longitude

Longitude is the angle, east or west, around the equa- tor to the point near est the location.

Perigee(moon)

Moon is close

Apogee(moon)

Moon is really far away(A away)

Local (apparent) Noon

Sun inline with meridian. About 1pm.

Solstice literally means

Sun-stop