ASTR 1210 Chapter 1 (Modern View)

solar system

a star and all the objects that orbit it

galaxy

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

Milky Way

galaxy where our solar system belongs to; huge, disk-shaped collection of stars; contains more than 100 billion stars that are mostly orbited by planets

Local Group

group of 80 + galaxies including the Milky Way are found

galaxy clusters

collection of galaxies bound together by gravity; groups of galaxies with many more large members

superclusters

regions where galaxies and galaxy clusters are tightly packed (clusters of galaxy clusters)

→ Local Supercluster (Local Group is inside)

universe

sum total of all matter and energy

astronomical unit

Earth’s avg. distance from the Sun

about 150 mil km

distances in our solar system with AU

light-year

• distance light can travel in 1 year

• about 10 trillion km

• use to describe the distance if stars and galaxies → UNIT OF DISTANCE

speed of light (one light second)

300,000 km/sec

light takes time to travel through space →

the farther we look in distance, the further we look in time

Andromeda Galaxy

the nearest large spiral galaxy to the Milky Way; about 2.5 million light-years away

star

large glowing ball of gas that generates heat and light through nuclear fusion (process where two smaller nuclei merge to form a larger nucleus) in its core

planet

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

it must:

1. orbit a star

2. large enough for gravity to make it round

3. has cleared most other objects from its orbital path

if it meets only the first two → dwarf planet

exoplanet

planet orbiting a star other than our sun

moon/satellite

object that orbits a planet

asteroid

relatively small and rocky object that orbits a star

comet

relatively small and ice-rich object that orbits a star

small solar system body

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

world

any planet, dwarf planet, moon, or small body we could imagine visiting

star system

star and any planets and other materials that orbit it

observable universe

portion of the entire universe that we can see from the Earth

rotation

spinning of an object around its axis

orbit/revolution

orbital motion of one object around another due to gravity

expansion (of the universe)

the increase in the average distance between galaxies as time progresses

boundary of the observable universe

14 billion light-years

distance formula

speed * time

astronomical scaling

divide by large #s

Birth of the Universe

expansion of universe began with hot and dense Big Bang, continues to expand on smaller scale, gravity pulls matter together to make galaxies

early universe composition

hydrogen and helium; all other elements made of stars and recycled from one stellar generation to the next

earth’s birth

around 2% of original hydrogen and helium had been converted into heavier elements

do galaxies expand?

no, while the overall universe continues to expand, individual galaxies and galaxy clusters do not

calendar scale

solar system + Earth didn’t form until early September (January 1st = Big Bang, December 31st = present time)

most basic motions of earth

daily rotation (spin) and its yearly orbit (revoolution) around the Sun

which direction does Earth rotate?

west to east → Sun and stars appear to rise in the east, set in the west each day (counterclockwise as viewed from the North Pole)

how fast is the Earth’s rotation?

more than 1000 km/hour

average Earth-Sun distance

1 AU

What does Earth’s orbital path define?

the ecliptic plane: a fkat surface that the Earth rotates relative to in a tilted manner

axis tilt

amount by which a planet’s axis is tilted with respect to a line perpendicular to the ecliptic plane

in what direction does the Earth orbit the Sun?

the same direction that it rotates on its axis

how do galaxies move?

galaxies move at random within the Local Group; any galaxies beyond the LG move away from us → farther galaxies = move faster

E-S distance

150,000,000 km

Diameter of sun

1,400,000 km

E-M distance

384,000 km

Diameter of E

12,800 km