Astronomy Vocabulary Set #1 Quiz Date = Thursday, March 30

the study of the moon, stars, and other objects in space Astronomy: the study of the moon, stars, and other objects in space  Astronomy includes mathematics, chemistry, and physics.

Axis: the imaginary line that passes through Earth's center and the North & South Poles The Earth's axis is tilted 23.5° from perpendicular.

the spinning of Earth on its axis Rotation: the spinning of Earth on its axis The Earth rotates from the west towards east. In the northern hemisphere, this is considered to be counter-clockwise. One rotation takes 24 hours.

Revolution: the movement of one object around another object When viewed from above the north pole, the Earth appears to revolve in a counter-clockwise direction around the Sun. One revolution takes 365.25 days.

the path an object takes as it revolves around another object in space Orbit: the path an object takes as it revolves around another object in space Earth's orbit is not a circle, but elliptical, or slightly oval-shaped. 

Solstice: the two days of the year on which the sun reaches its greatest distance north or south of the equator shortest day of the year longest day of the year around December 21 around June 21

Equinox: the two days of the year on which the noon sun is directly overhead at the equator Spring Equinox Fall Equinox Around March 21 Around September 21 The length of day and night is nearly equal.

the force that attracts all objects toward each other Gravity: the force that attracts all objects toward each other Even though Sir Isaac Newton is credited for ‘discovering’ gravity, ancient scientists and mathematicians from the 5th century were already aware of this force which holds the universe together.

Law of Universal Gravitation: the scientific law that states that every object in the universe attracts every other object For any two objects, the gravity between the objects depends on their mass and distance. The greater the mass, the stronger the gravity; the greater the distance between, the weaker the gravity.

The amount of matter in an object Mass The amount of matter in an object Mass is how heavy something is without gravity.  This means the mass of an object is the same on earth and in space (or other planets)

Weight: the force of gravity on an object Mass and weight are NOT the same. Weight has the additional factor of gravitational pull. Divide your current weight by 6; that’s how much you would weigh on the moon. Do you know why?

the tendency of an object to resist a change in its motion Inertia: the tendency of an object to resist a change in its motion The amount of inertia depends on the mass of the object. Which would have more inertia, an elephant or a mouse? A golf ball or a ping pong ball?

one of the different apparent shapes of the moon as seen from Earth Phase: one of the different apparent shapes of the moon as seen from Earth The moon does not make its own light; it reflects sunlight. The lunar month is 29 days long.

Solar eclipse: the blocking of sunlight to Earth that occurs when the moon is directly between the sun and the Earth Generally, there are only two solar eclipses every year.

the darkest part of a shadow Umbra: the darkest part of a shadow All of the light from the source is blocked.

the part of the shadow surrounding the darkest part Penumbra: the part of the shadow surrounding the darkest part The shadow is only partial, or imperfect.

Lunar eclipse: blocking of sunlight to the moon when Earth is directly between the sun and the moon Generally, there are two to four lunar eclipses each year.

Maria: dark, flat areas on the moon's surface formed from huge, ancient lava flows Ancient astronomers mistook these dark areas for seas; the Latin word for ‘seas’ is maria. The most famous of these is the Sea of Tranquility.

Orbital velocity the velocity a rocket must achieve to establish an orbit around a body in space This velocity has to be just right to maintain orbit; the distance to the center of the Earth is always the same.

Escape velocity: the velocity a rocket must reach to fly beyond a planet's gravitational pull From Earth’s surface, escape velocity is about 25,000 miles per hour, the minimum speed required to escape the Earth without ever falling back.