ASTR 122 Final Study Guide

light-years

a unit of astronomical distance equivalent to the distance that light travels in one year

Newton’s Law of Gravitation

every particle in the universe attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of their distance.

absorption line spectrum definition

decrease in intensity of radiation at specific wavelengths (pattern of dark lines or bonds)

Absorption line spectrum source

produced when photons from a hot, broad spectrum pass through cooler material.

emission spectrum definition

range of wavelengths emitted when an atom is excited by heat or radiation

emission spectrum source

this will appear if the source emits specific wavelengths of radiation. When an atom, element, or molecule in an excited state returns to a configuration of lower energy

absorption

lines are where light has been absorbed by the atom, thus you see a dip in the spectrum

emission

lines have spikes in the spectrum due to atoms releasing photons at those wavelengths

Composition of the sun

92.1% hydrogen and 7.9% helium

Sun’s Source of Power

nuclear fusion, which is when protons of hydrogen atoms violently collide in the sun’s core and fuse to create a helium atom (pp chain!)

absolute brightness

how much energy is coming from the star per square meter per second, as measured on earth

luminosity

the intrinsic brightness of a celestial object

distance

measures length between objects or points without regard for direction

stellar color

provides direct measurement of its surface temperature

hottest stars

blue-white

coolest stars

dull red-orange

Hottest and largest type of star

o type star

smallest and coolest type of star

m type star

brown dwarf

have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars

H-R Diagram definition

scatterplot of stars showing the relationship between the star’s absolute magnitudes or luminosities versus their stellar classifications or effective temperatures

how the H-R diagram works

stars are ranked from bottom to top in order of decreasing magnitude (increasing brightness) and from right to left by increasing temperature (spectral class)

How to tell the age of star clusters with an HR diagram

look at the main sequence turnoff point and compare it with models of stellar evolution

What do stars start off as?

Cloud of gas and dust

What do stars turn into once the cloud of dust and gas is rotated and flattened?

Protostar

What happens after a star becomes a protostar?

The hydrogen atoms begin to fuse into helium

Event horizon

a black hole’s surface that defines the boundary where the velocity needed to escape exceeds the speed of light.

rotation curve

a plot showing how orbital velocity (V) varies with distance from the center of the object (R)

dark matter

composed of particles that do not absorb, reflect, or emit light, so they cannot be detected by observing electromagnetic radiation

Where does star formation take place in the milky way galaxy?

spiral arms where the density of interstellar matter is highest

What type of light can we use to see the center of the milkyway galaxy?

infrared light to see through the dark clouds of dust

What percent of the milky way is made up of dark matter?

95%

Big Bang

an event that describes how the universe expanded from an initial state of high density and temperature and then expanded and stretched to grow as large as it is now

recombination

the epoch during which charged electrons and protons first became bound to form electrically neutral hydrogen atoms

epoch

a moment in time used as a reference point for some time-varying astronomical quantity

Cosmic Noon

after the cosmic dawn ended, galaxies continued to grow at faster rates, until 3 billion years after the big bang. By this time, a “typical” galaxy was hundreds of times larger than its progenitors during the cosmic dawn

Cosmic Dawn

occurred about 100 million to 1 billion years after the big bang, this is marked by the formation of the universe’s first stars and galaxies

CMB

leftover radiation from the big bang that formed 400,000 years after the big bang

cluster

groups of ten or more stars that were formed from the same interstellar cloud

void

vast spaces between filaments, which contain very few or no galaxies

supercluster

a group of galaxy clusters typically consisting of 3 to 10 clusters and spanning as many as 200,000,000 light years

hubble time

the ratio of the speed of the recession of a galaxy (due to the expansion of the universe) to its distance from the observer

redshift

the wavelength of the light is stretched, so the light is seen as shifted towards the ___ part of the spectrum

What represents the relationship between recession velocity of a galaxy and its distance?

Hubble’s Law (Vr = H d)

What is causing the changes and the expansion of the universe?

at first, the changes gradually slowed down due to the pull of gravity on itself. then, 5 or 6 billion years after the big bang, dark energy began speeding up the expansion of the universe again

Dark energy

makes up 68% of the universe