AS101 Midterm 1

solar system

consists of the Sun, the planets and their moons, and countless smaller objects

galaxy clusters

groups of galaxies with more than a few dozen members

superclusters

the regions in which galaxies and galaxy clusters are most tightly packed

stars and galaxies

what we generally use light-years to describe the distances of

star system

a star and any planets and other materials that orbit it

cluster of galaxies

a collection of galaxies bound together by gravity

observable universe

the portion of the entire universe that can be seen from Earth, at least in principle.

rotation

the spinning of an object around its axis

orbit (revolution)

the orbital motion of one object around another due to gravity

Milky Way Galaxy

the galaxy our solar system belongs to

galaxy

a great island of stars in space, containing more than 100 billion stars

local group

group of about 40 galaxies including the milky way

universe

the sum total of all matter and energy, encompassing the superclusters and voids and and everything within them

astronomical unit (AU)

1 is Earth's average distance from the sun. = to about 150 million km

light-year

the distance that light can travel in 1 year. = to about 10 trillion km

solar system

what we commonly describe distances in AU within this

star

a large, glowing ball of gas that generates heat and light through nuclear fusion in its core

planet

a moderately large object that orbits a star and shines primarily by reflecting light from its star

moon

an object that orbits a planet

satellite

also can be a moon because it orbits a planet

asteroid

a relatively small and rocky object that orbits a star

comet

a relatively small and ice-rich object that orbits a star

small solar system body

an asteroid, comet, or other object that orbits a star but is too small to qualify as a planet or dwarf planet

dwarf planet

an object that meets the first 2 criteria of being a planet but has not cleared its orbital path

expansion (of the universe)

the increase in the average distance between galaxies as time progresses

14 billion light-years

the boundary of our observable universe

alpha centauri

the nearest star system to our own

big bang

the beginning, the point at which expansion began

nuclear fusion

the process in which light-weight atomic nuclei smash together and stick to make heavier nuclei

supernovae

when massive stars die in titanic explosions

ecliptic plane

the flat plane defined by Earth's orbital path

axis tilt

tilt from a line that is perpendicular to the ecliptic plane

celestial sphere

map of the sky seen from earth

north celestial pole

the point located directly over Earth's north pole

south celestial pole

the point directly over earth's south pole

celestial equator

a projection of earth's equator into space, makes a complete circle around the celestial sphere

ecliptic

the path the sun follows as it appears to circle around the celestial sphere once each year

local sky

the sky as seen from wherever you happen to be standing

horizon

the boundary between the earth and the sky

zenith

the point directly overhead

meridian

imaginary half circle stretching from the horizon due south, through the zenith, to the horizon due north

angular size

the angle an object appears to span in your field of view

angular distance

the angle that appears to separate two objects

circumpolar

when a star near the north celestial pole remains perpetually above the horizon, circling counterclockwise around the north celestial pole each day

zodiac

the constellations along the ecliptic

summer solstice

in June, moment when the northern hemisphere is tipped most directly toward the sun and receives the most direct sunlight

winter solstice

in December, moment when the northern hemisphere receives the least direct sunlight

spring equinox

in March, moment when the northern hemisphere goes from being tipped slightly away from the sun to being tipped slightly toward the sun

fall equinox

in September, moment when the northern hemisphere first starts to be tipped away from the sun

precession

gradual wobble that alters the orientation of Earth's axis in space

lunar phases

when the moon's appearance in our sky changes as its position relative to the sun changes

synchronous rotation

the moon rotates on its axis in the same amount of time it takes to orbit Earth

eclipse

when the sun, moon, and earth fall into a straight line

lunar eclipse

when earth lies directly between the sun and moon, so earth's shadow falls on the moon

solar eclipse

occurs when the moon lies directly between the sun and earth so the moon's shadow falls on earth

nodes

the two points in each orbit at which the moon crosses the surface

umbra

where sunlight is completely blocked

penumbra

where sunlight is only partially blocked

total lunar eclipse

if the sun, earth, and moon are nearly perfectly aligned, the moon passes through earth's umbra

partial lunar eclipse

alignment of sun, earth, and moon is less perfect, only part of the full moon passes through the umbra

penumbral lunar eclipse

if the moon passes through only earth's penumbra; most common type of lunar eclipse

totality

when the moon is entirely engulfed in the umbra, moon becomes dark and eerily red

total solar eclipse

the moon's umbra can cover a small area of earth's surface

annular eclipse

a ring of light around the moon- in the small region of earth directly behind the umbra.

partial solar eclipse

only part of the sun is blocked from view

eclipse seasons

the two periods each year when the nodes of the moon's orbit are nearly aligned with the sun. lasts a few weeks.

saros cycle

when eclipses recur in a cycle of about 18 years, 11 3/4 days

apparent retrograde motion

when planets occasionally reverse course, moving westward through the zodiac

stellar parallax

the apparent shift in the position of a nearby star that occurs as we view the star from different positions in Earth's orbit of the sun each year

geocentric model

Greek, placed a spherical Earth at the center of the universe

ptolemaic model

ptolemy's geocentric model, explained apparent retrograde motion

copernican revolution

what changed the way we perceive our place in the universe

supernova

explosion of a distant star

ellipse

planetary orbits are a special type of oval

foci

the locations of the 2 tacks of the ellipse

major axis

the long axis of the ellipse

semimajor axis

each half of major axis

minor axis

the short axis

eccentricity

quantity that describes how much an ellipse is stretched out compared to a perfect circle

kepler's laws of planetary motion

summary of kepler's discoveries with 3 simple laws

perihelion

when a planet is closest to the sun

aphelion

when a planet is farthest from the sun

paradigm

general patterns of thought

theory

when a powerful yet simple model makes predictions that survive repeated and varied testing

speed

how far something goes in a certain amount of time

velocity

the speed and direction of something

acceleration

if velocity is changing in any way, whether in speed or direction or both

acceleration of gravity

acceleration of a falling object

momentum

the product of its mass and velocity

force

to change an object's momentum you apply:

net force

overall force acting on an object

angular momentum

circling or turning momentum

torque

type of force that changes an object's angular momentum, "twisting force"

mass

amount of matter in something

weight

the force on something

free-fall

falling without any resistance to slow the object down

weightless

when something is in free-fall it is:

first law

newton's law that an object moves at constant velocity if there's no net force acting upon it

second law

newton's law that force=mass x acceleration

third law

newton's law that for any force, there is always an equal and opposite reaction force