ASTRONOMY 101

Light Year

the distance light travels in one year

Constellation

A group of stars that form a pattern in the sky

Celestial Sphere

An imaginary sphere surrounding Earth to which the stars are attached and are thought to be on its inner surface

Ecliptic

imaginary Plane that contains Earth's orbit around the Sun.

Summer Solstice

Day with the most hours of sunlight and the fewest hours of darkness

Winter Solstice

exact moment when half of the Earth is tilted the farthest away from the sun

Equinoxes

a point at which, everywhere on Earth, days and nights are nearly equal in length

Latitude

position north or south of equator

Longitude

position east or west of prime meridian

Phases of the Moon

caused by changing positions of the Moon, Earth, and Sun

Eclipses

When the earth, moon, and sun are perfectly aligned on the same plane.

Precession

rotation of Earth's axis itself; makes one complete circle in about 26,000 years

Rotation

circular motion of an object around its center

Revolution

objects orbital motion around another object

New Moon

Waxing Cresent

First Quarter

Waxing Gibbous

Full Moon

Waning Gibbous

Last Quarter

Waning Cresent

Planet

A moderately large object that orbits a star; it

shines by reflected light. Planets may be

rocky, icy, or gaseous in composition

Moon

An object that orbits a planet

Asteroid

A relatively small and rocky object that orbits a star

Comet

A relatively small and icy object that orbits a star

Nebula

An interstellar cloud of gas and/or dust

Star

A large, glowing ball of gas that generates heat and light through nuclear fusion

Solar System

A star and all the material that orbits it, including its planets and moons

Galaxy

A great island of stars in space, all held together by gravity and orbiting a common center

Universe

The sum total of all matter and energy; that is, everything within and between all galaxies

Order of Phases of Moon

New Moon → Waxing Crescent → First Quarter → Waxing Gibbous → Full Moon → Waning Gibbous → Last Quarter → Waning Crescent

Planetary Motion

Describe the characteristics of planetary motion

1. Planetary orbits are ellipses, Sun at one focus

2. Imaginary line connecting Sun and planet

sweeps out equal areas in equal times

3. Square of period of planet's orbital motion

is proportional to cube of semimajor axis

Contributions of Galileo

Galileo's contributions:

-Galileo investigated this

connection with

experiments using

projectiles and balls rolling

down planks

-He put science on a

course to determine laws

of motion and to develop

the scientific method

Kepler's Laws (3 Total)

-Kepler's First Law (Law of Ellipses): Planets orbit the Sun in an ellipse, with the Sun at one focus.

-Kepler's Second Law (Law of Equal Areas): Planets move faster when they are closer to the Sun and slower when they are farther away.

-Kepler's Third Law (Law of Harmonies): Planets farther from the Sun take longer to orbit than planets closer to the Sun.

Newton's Laws (4 Total)

1. An object at rest will remain at rest, and an object

moving in a straight line at constant speed will

not change its motion, unless an external force

acts on it.

2. When a force is exerted on an object, its

acceleration is inversely proportional to its mass: a = F/m

3. For every action, there is an equal and opposite reaction.

4. Law of Universal Gravitation: All objects attract each other with a force based on their masses and the distance between them.

Ptolemaic Model

Earth-centered model of the universe (everything orbits Earth).

Copernican Model

Sun-centered model of the universe (planets orbit the Sun).

Planetary Motion

Describe the characteristics of planetary motion:

-Planets orbit the Sun in ellipses, not perfect circles.

-The Sun is at one focus of each planet's orbit.

-Planets move faster when closer to the Sun and slower when farther away.

-Outer planets take longer to orbit the Sun than inner planets.