Astro 101 Midterm 1 terms

constellation

a recognized pattern/group of stars in the sky

ecliptic

the imaginary path the Sun appears to follow across the sky during the year

zodiac

a band of constellations along the ecliptic, where the Sun, Moon, and planets appear to move

celestial equator

an imaginary line in the sky directly above Earth’s equator

celestial pole

a point in the sky directly above Earth’s North or South Pole, around which the stars appear to rotate

circumpolar

an object/star that never rises or sets from a particular location because it stays above the horizon

lunar eclipse

when Earth gets between the Sun and Moon, causing Earth’s shadow to fall on the Moon

solar eclipse

when Moon gets between the Sun and Earth, causing the Moon’s shadow to fall on Earth

direct motion

the normal direction a planet appears to move across the sky, generally west to east relative to the stars

retrograde motion

when a planet appears to temporarily move backward against the background stars

inferior planet

a planet whose orbit is inside Earth’s orbit around the Sun, seen around sunrise/sunset

superior planet

a planet whose orbit is outside Earth’s orbit, seen @ diff times during night

Ptolemy’s geocentric model

an earth-centered model of the universe

Copernicus’ heliocentric model

a sun-centered model

ellipse

a stretched-out or oval-shaped circle

astronomical unit

a unit used to measure distances in our Solar System (1AU)

average distance from Sun

the average distance a planet is from the Sun over its orbit

orbit period

the amount of time it takes an object to complete one full orbit

speed

how fast something is moving

velocity

speed and direction

acceleration

a change in velocity over time

force

a push or pull on an object

net (unbalanced) force

the total/overall force acting on an object after all the forces are combined

mass

the amount of matter in an object

weight

the force of gravity acting on an object’s mass

orbit

the curved path an object follows around another object because of gravity

weightlessness

a condition where you feel as though you have no weight, usually because you are in free fall

orbital velocity

the speed an object needs to have to remain in orbit around another object

escape velocity

the minimum speed needed for an object to escape a body’s gravitational pull without additional propulsion (speed to get away)