AST1002

Accelerated

Change in a celestial bodies speed or direction of motion

Angular Momentum

Measurement of the rotation of a body as it revolves around some fixed point

Aphelion

The point in a planet's orbit that is farthest from the sun

Apogee

The point in an orbit most distant from the body being orbited; the highest point

Apparent Magnitude

The brightness of a star when viewed from Earth

Apparent Solar Time

time as measured by the position of the Sun in the sky (the time that would be indicated by a sundial)

Asteroid Belt

the region of the solar system between the orbits of Mars and Jupiter, where many asteroids are found

Astrology

study of the stars

Astronomical Unit

the average distance between the earth and the sun

Celestial Equator

The projection of the earth's equator onto the celestial sphere

Celestial Poles

The extension of the Earth's north and south pole onto the celestial sphere

Celestial Sphere

An imaginary sphere surrounding Earth to which the stars are attached

Circumpolar Zone

The part of the sky that is always above the horizon as seen from your location

Cosmology

Study of the universe

Declination

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

Density

The degree of compactness of a substance.

Eccentricity

A measure of the elongation of an ellipse

Ecliptic

Path of the sun and the planets

Ellipse

A elongated circle, or oval shape, the shape of the planets orbit.

Epicycle

Circle within a circle

Escape Speed

The speed a body must achieve to break away from the gravity of another body

Focus

The two points inside an ellipse

Geocentric

A model of the universe in which Earth is at the center of the revolving planets and stars.

Longitude

Distance east or west of the prime meridian, measured in degrees

Lunar Eclipse

The blocking of sunlight to the moon that occurs when Earth is directly between the sun and the moon

Major Axis

The longer axis of an ellipse, passing through its foci.

Mean Solar Time

Time kept according to the average length of the solar day

Meridian

An arc drawn on a map between the North and South poles.

Gravity

A force of attraction between objects that is due to their masses.

Great Circle

The intersection of a sphere and a plane that contains the center of the sphere

Heliocentric

Based on the belief that the sun is the center of the universe

Horizon

The line at which the sky and Earth appear to meet

Horoscope

A prediction of someone's future based on the relative positions of the planets

International Date Line

The line of longitude that marks where each new day begins, centered on the 180th meridian

Kepler's First Law

The orbits of the planets are ellipses, with the sun at one focus

Kepler's Second Law

As a planet moves around its orbit, it sweeps out equal areas in equal times

Kepler's Third Law

The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

Latitude

Distance north or south of the Equator, measured in degrees

Momentum

The force or speed with which something moves

Neap Tides

A tide just after the first or third quarters of the moon when there is the least difference between high and low water.

Spring Tides

A tide just after a new or full moon, when there is the greatest difference between high and low water.

Newton's First Law

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Newton's Second Law

Force equals mass times acceleration

Newton's Third Law

For every action there is an equal and opposite reaction

Orbit

The path of an object as it revolves around another object in space

Orbital Speed

The speed at which an object (usually a planet) orbits around the mass of another object

Parallax

An apparent shift in the position of an object when viewed from different locations

Perigee

Point in an orbit that is closest to the earth

Perihelion

Orbital point nearest the sun

Precession

Wobble in Earth's rotational axis

Prime Meridian

The meridian, designated at 0° longitude, which passes through the Royal Observatory at Greenwich, England.

Retrograde Motion

A planet's apparent backward movement in the sky.

Right Ascension

The coordinate for measuring the east-west positions of celestial bodies

Satellite

An object that revolves around another object in space

Semimajor Axis

Half of the major axis

Sidereal Day

The time for one complete rotation of the earth relative to a particular star, about 4 minutes shorter than a mean solar day

Sidereal Month

Time required for the Moon to complete one trip around the celestial sphere.

Solar Day

Earth's rotation period as defined by the position of the Sun in the sky, 24 hours

Solar Month

The time interval in which the phases repeat—say, from full to full phase

Synchronous Rotation

The rotation of an object that always shows the same face to an object that it is orbiting because its rotation period and orbital period are equal

Tides

The regular rise and fall of the ocean's surface influenced by the moon's gravity pulling on earth

Tropic of Cancer

23.5 degrees North

Tropic of Capricorn

23.5 degrees South

Velocity

The speed of an object in a particular direction

Year

The time required for the Earth to orbit once around the sun

Zenith

The highest point

Zodiac

A band of 13 constellations around the sky through which the Sun appears to move throughout the year.