BBtHK Exam 1 Review

How old is Earth?

4.6 billion years old

How old is the universe?

13.8 billion years old

How long ago did planets form in our galaxy?

4.6 billion years ago

what is science?

a process that seeks the truth but is always changing

Sidereal day

the time it takes for the Earth to rotate once on its axis relative to the fixed stars (inertial space)

1 AU (astronomical unit)

average distance between the sun and the Earth (93 million miles, 8 light minutes)

why is everything we study in astronomy in the past?

because light takes time to travel, for example the nearest star and exoplanets are are 4.2 light years away

1 parsec

3.3 light years (the distance it takes light to travel in one year)

1 light year (ly)

1×10^13 km, most stars are 100s-1000s light years away

Milky Way galaxy

• contains about 200 billion stars

• 75k light years across

• frisbee shape

• darkness: presence of gas and dust (where new stars and planets form)

Andromeda Galaxy

only large galaxy you can see with the naked eye, similar to our galaxy, 2.5 million light years (ly) away (tiny galaxies are billions of ly away)

Light wavelengths

wavelengths range from the size of an atom’s nucleus to the size of a mountain

• short wavelengths: higher energy, blue

• long wavelengths: lower energy, red

anything with temperature gives off light

• thermal radiation

• hotter objects = “bluer” & brighter

• cooler objects = “redder” & dimmer

water on earth

• 1 universal thing about life

• less than 1/10th of the percent of earth is covered by water

• water is here from extraterrestrial source

earth’s atmosphere

mostly nitrogen (from volcanic activity) and oxygen (from life)

spectroscopy

allows us to look at distant chemical components and tell what something is made of

• anything with temperature gives off light

• thermal radiation gives off characteristic shapes

blue light

hotter than the sun, the hottest type of light

temperature

measure of kinetic energy (how fast molecules are moving)

Why does a leaf appear green to the human eye?

because it takes in every color except green and reflects it

• the sun has all of the colors

• rainbows (light spreads from the sun to water in the sky)

• colors can combine

gaps in solar spectrums

absence of light & gaps in wavelengths, sun is not a continuous rainbow

• specific elements in the sun absorbing specific wavelengths of light

the power of spectroscopy

can tell you what things are made of

• every element on the periodic table has its own colors & wavelengths it wants to absorb

• electrons inside the atom are gaining energy

UV rays

are not visible

• higher UV: ozone on the earth is weaker

• sun is brightest in the visible but most energy in the infrared

what is the most important greenhouse gas?

water, not CO2

doppler effect for light

as something moves towards you it gets bluer & moves away from you it gets redder

• redshift: away from you

• blueshift: towards you

• this tells us about direction and speed (velocity)

2 main takeaways from spectroscopy

1. a spectrum of an object tells us what its made of, no matter where it is in the universe

2. tells us how fast its moving towards or away from us

true or false: the earth orbits the sun

false!

Vesto Slipher

Lowell observatory, spectroscopy of galaxies

Henrietta Swan Leavitt

Harvard “computer” who discovered Cepheid Variables as the first “standard candles”

• they’re pulsing stars, pulse in a regular pattern

• Cepheids w/ longer periods are brighter

standard candle

you know intrinsically how bright it is (like an 100 watt light bulb)

parallax

we can calculate intrinsic brightness by measuring how fast a star moves back and forth

• we can’t put things into relative distance unless they’re standard candles or parallax

Hubble Law

objects farther away are moving faster

the universe is expanding:

uniformly

History of the Universe Model

• Lemaitre proposed this model

• early universe: so dense & hot that light can’t get out (light could escape at 500k years old)

Cosmic Microwave Background Radiation

light leftover from the Big Bang

• we can see it in all directions: colors indicate temp. difference of 1/1000 of a degree

• best evidence we have for the Big Bang

beta decay

neutrons don’t like to be neutrons on their own, so they have a 10 minute half life

• if they’re just floating around they become a proton

• 10 min half-life: after 10 mins, half of the neutrons are gone

first 3 minutes of the universe

all of the hydrogen was made, helium as well

nucleosynthesis

early universe is hot enough to smash together sub-atomic particles

• proton + neutron = element

• type of nuclear fusion

• big bang produced He, H, Li, Be

dark energy

• responsible for the universe accelerating

• different from dark matter

• we don’t know anything else about it

dark matter

likely a subatomic particle, making it really hard to detect

• the universe is filled with matter we know very little about

Vera Rubin

one of the pioneers of dark matter

• used doppler shift to measure galaxy rotation

• galaxies are rotating faster than they should (by a lot) = dark matter, which doesn’t give off light at all

• maybe a property of space itself

what is the force of gravity based on?

mass and distance

• gravity has no bounds according to distance

why is the universe getting a lot darker every day?

because some galaxies are expanding faster than the speed of light

when you bend space, you are:

altering time

at which temperature do stars become stars?

10 Million kelvin

Annie Jump Cannon

Harvard “computer” who worked on stellar spectral classification, based on the strength of the hydrogen lines

Cecilia Payne

first female full professor of astronomy at Harvard

• in her PhD thesis she said that the sun was made of hydrogen and helium

properties of stars

every property of a star foretold by its mass

• temperature controls spectral features

Hertzsprung Russell Diagram

a plot of luminosity, intrinsic brightness vs its color (temperature)

• spectral types: O, B, A, F, G, K, M, L, T, Y

• also a mass sequence: bigger stars are brighter and bluer to the left, smaller stars are dimmer and redder to the right

• sun is average, main sequence, in the middle (goldilocks)

• 80% of stars are M or L type, which are too small to be seen by the naked eye

nuclear fusion (proton-proton chain)

single protons heated to about 10 M kelvin will smash together

what do you get when you smash 4 hydrogen protons together at 10 M kelvin?

helium & light

• this is how the sun shines

lifetimes of massive stars

the most massive stars have lifetimes that are less than 1 million years

• less efficient (shorter lifetimes)

lifetimes of small stars

are more efficient than large stars, so they have longer lifetimes

track 1

tiny stars that live forever

what will eventually happen to the sun?

it will run out of gas and expand to become a red giant. in 5 billion years the sun will die and so will everything around it. then the sun will become a planetary nebula and then a white dwarf.

hydrastatic equilibrium

hydrogen gas and gravity are in equilibrium

• sun + gravity = temperature

triple-alpha process

it gets so hot that 3 helium atoms can be fused together to create carbon. eventually you run out of helium, fuse it with carbon and get oxygen during the red giant phase. then iron is made.

what’s the most important atom in our world?

carbon

what is the only place in the whole universe that carbon is made?

in the center of a dying star

stellar nucleosynthesis

it gets so hot that 3 helium atoms can be fused together to create carbon. eventually you run out of helium, fuse it with carbon and get oxygen during the red giant phase. then iron is made.

• this is how elements 5 - 26 on the periodic table are made

white dwarf stars

are the mass of stars but the size of Earth (very dense)

• large amount of gravity!

• they slowly cool down to nothing and hoard elements

what types of stars eventually turn into red giants?

all stars except for little ones

track 3

mid mass star —> red giant —> supernova —> neutron star

• late/end stellar nucleosynthesis

• if stars are 8x to 24x as massive as the sun, they will eventually explode as supernovas, which scatters elements

• this is how all gold was made

Jocelyn Bell-Burnell

hypothesized neutron stars

track 4

high mass star —> red giant —> supernova —> black hole

• star has to be about 25 more times more massive than the sun

track 2

low mass star —> red giant —> planetary nebula —> white dwarf

what are black holes?

they are a single point in space with:

• no volume

• no size

• mass

• infinite density

they happen after supernovas, warp time (they slow it down like in the movie Instellar)

solar system by mass

• hydrogen 74%

• helium 24%

• NH3 + H2O + CH4 + iron + rocks equate to 2%

what percent of the universe does the sun equate to?

99.99%

what is the density of water?

1.0 g/cm3

what is the density of ice?

0.9 g/cm3

what is the density of rock?

3.0 g/cm3

what is the density of iron?

7.9 g/cm3

What makes up the planet Mercury if it has a density of 5.4 g/cm3?

rock & iron

what is a terrestrial world?

a world that you can physically walk on

• ex. earth, mercury, moon

• you can only use density to determine what a planet is made out of if its terrestrial

define the relationship between distance to the sun and density of terrestrial worlds

closer: more dense

farther: less dense

frost line

• ice can form at 3 AU

• it is so hot inside the frost line that everything is in vapor/gas form (even rock & iron)

• outside the frost line, it cools down, so water and ice can form

• no planets at the frost line

can worlds be built with water and ice inside the frost line?

no, they have to be built with iron or rock, as water and ice are purely vapor (they only form outside the frost line.

what happens outside of the frost line?

water & ice can form, worlds can be formed with ice, water, rock, and iron.

Condensation Sequence

the temperature at which materials condense in the solar nebula

• denser material condenses at higher temperatures

relationship between planet size and frost line

planets inside the frost line are smaller

• jupiter, which is outside the frost line, had access to more material while it was forming so it is bigger than planets inside the frost linei

what are ice giants?

planets like Neptune & Uranus have a lot of ice and rock

• they don’t accumulate material quickly because they take longer to orbit the sun

solar wind process

the sun blows out gas within a few million years

• if planets are orbiting it faster, than they accumulate more material

• Jupiter could get a lot more material in the first few million years

radiometric dating of rocks

starting with Marie Curie, it was discovered that many rocks contain radioactive elements that decay to new elements

• this helps us assign dates/ages to rocks

• common types include potassium —> argon

what are the five stages of planetary evolution?

1. origin

2. differentiation

3. late heavy bombardment

4. geological activity

5. the big chill

what is the earth mostly made of?

O, Fe, Si, and Mg

• 99.8% of earth’s water is locked up inside rock

late heavy bombardment

material left over from the Big Bang hit planets

• life started sooner than we previously thought

earth’s volcanism

earth is active

• interior is being heated

• radioactive heating is responsible for motions inside the earth

• earth’s core is as hot as the surface of the sun

how does the earth stay molten?

nuclear fission (decay) off uranium, potassium, thorium

• when a world runs out of radioactive material = the big chill (size matters for this)

magnetic fields

• from physics: moving charge creates a magnetic field

• earth rotates (1 rotation = 24 hours)

Earth’s axis

tilted axis of 23.5 degrees

• 1 rotation for every 24 hours

• hot inside (charges can move)

what are the 2 conditions of a magnetic field?

a planet has to have geologic activity & fast rotation

on which pole does earth rotate?

the geographic pole (the earth’s magnetic fields flip polarity once in a while)

what does the magnetic field of the earth protect us from?

solar wind (high energy particles)

how much of the earth is water?

about 0.1% of the earth is water

• most of the worlds have as much or more water than earth

carbonaceous chondrites

rocks that have similar composition to the material that was hitting the earth during its formation

• are dated to 4.6 billion years old!

• some have water, organic materials

Alfred Wegner

in 1912, he proposed the idea that all continents were one supercontinent in the past

• rocks: geological similarities across long distances

• fossils: animal fossils were the same across entire oceans

• climate: coal deposits found in Antarctica, glacier deposits in Africa, India, and Australia

• continents fit together like a puzzle

Marie Tharp

a cartographer who profiled maps of the ocean floor

• her maps supported the continental drift theory

paleomagnetism

reconstructs the magnetic past, which helped to confirm tectonic plate movement and support the continental drift theory

• distance + time = a rate of movement

how many times have the earth’s magnetic poles flipped polarity?

183 reversals over the last 83 million years

convection and tectonic plate movement

convection in the mantle pushes up magma, which in turn makes the continents “surf” on the convective currents and move