AST101 Midterm

the universe

the further we look away, the further back in time we look, the universe is cooling and expanding, the universe is transparent now, but back then it wasn’t

Primordial plasma

13.7 billion years ago, red stuff at the edge of the universe

Orbit

• planet all ___ in the same plane (ecliptic plane)

• the planets all ___ in the same direction

• the sun rotates in the same direction that the planets ___

• the planes all have elliptical orbits

• the closer the planet is to the sun, the faster it ___

Mercury

• closest to the sun

• no atmosphere

• highly cratered surface

• rocky exterior with huge iron core

• temprature between -170 to 427 

• no moons

Venus

• roughly same size as earth

• lots of volcanos

• thick CO₂ atmosphere 

• runaway greenhouse effect which makes it hotter than mercury

• its always 460c everywhere

• rains acid

• no moons

• rotates very slowly backwards

Earth

• around same size as Venus

• lots of volcanoes

• O₂ + N₂ atmosphere

• large oceans regulate CO₂

• one large moon

• 23.4 degree orbital tilt produces significant seasons

Mars

• lots of volcanoes

• thin CO₂ atmosphere 

• oceans have evaporated

• no evidence of life

• 2 small moons

• polar ice/ dry ice caps

• dust storms

• 25.2 degree orbital tilt produces significant seasons

terrestrial planets

• small 

• rocky

• relatively thin or no atmosphere 

• few moons

• made from heavy elements

• (Earth, Venus, mercury, Mars)

Jupiter

• largest planet in the solar system

• thick gaseous atmosphere surrounds a giant ball of liquid hydrogen

• has very faint rings

• many moons: more than 60

Saturn

• second largest in solar system

• has rings

• many moons: more than 60

• structure like Jupiter

Uranus

• coldest planet

• small rocky core

• thick H₂/ He atmosphere

• rotation axis tilted 98 degrees

• thin rings and lots of moons

Neptune

• furthest planet from the sun

• structure similar to Uranus

• rotation axis tilted 28 degree

• more surface features than Uranus

• strongest words in the solar system: up to 21,000 Km/h

Jovian Planets

• Gas + Liquid

• large

• many moons

• mostly light elements

• (Jupiter, Saturn, Uranus, Neptune)

Asteroid Belt

• Around a million asteroids larger than 1km diameter

• total mass is around 3% of the moon’s 

Kuiper Belt

• Vast collection of small icy bodies beyond the orbit of Neptune

• includes several of the dwarf planets, including Pluto

• total mass around that of the earth’s moon

Comets

• smaller icy bodies from the outer solar system

• highly elliptical orbits

• emit tails when they get close to the sun

Summer

• daylight is longer and darkness is shorter

• sun gets higher in the sky, so sunlight is more direct

Winter

• daylight is shorter and darkness is longer

• sun does not get as “high” in the sky, so sunlight is at an angle

Moon phases and eclipses

• the sun illuminates one side of the moon. the other side is in shadow

• the phase we see depends on where the moon is compared to the sun

• phases repeat each time the moon orbits the earth once

• a solar eclipse happens when the moon blocks the sun

• a lunar eclipse happens when the moon enters the Earth’s shadow. This is not the cause of phases

New Moon

• when the moon is in the direction of the sun

• the only time a solar eclipse can happen

• unlit side faces the earth

• rises with the sun and sets with the sun

• not generally visible

waxing crescent

• 3-4 days after the new moon

• rises around 3 hours after the sun

• sets around 3 hours after the sun 

• easiest to see right after sunset

waxing quarter

• 1 week after the new moon

• moon is lit from the side

• rises around 6 hours after the sun

• sets around 6 hours after the sun

• easiest to see at night before midnight

waxing gibbous

• 10-11 days after the new moon

• rises around 9 hours after the sun

• sets around 9 hours the sun

• easiest to see at night - but may set before sunrise

full moon

• 2 weeks after the new moon

• the only time a lunar eclipse can happen 

• rises around 12 hours after the sun rises

• sets around 12 hours after the sun sets

• visible most of the night

waning gibbous

• 10-11 days before the next new moon

• rises around 3 hours after the sun rises

• rises before midnight, and is up the rest of the night

waning quarter

• around a week before the next new moon

• rises around 6 hours before the sun rises

• sets around 6 hours before the sun sets

• rises around midnight, and is up the rest of the night and morning

waning crescent

• 2-4 days before the next new moon

• rises around 3 hours before the sun rises

• sets around 3 hours before the sun sets

• easier to see before sunrise

solar eclipse

• when the moon blocks light from the sun

• happens when the new moon crosses the ecliptic plane

• because the moon’s orbit is tipped relative to the ecliptic plane, this happen rarely (every few years, somewhere on earth)

• it only casts a shadow on small part of earth

Lunar Eclipse

• when the moon enters the earth’s shadow

• happens when a full moon crosses the ecliptic plane

• can be seen from anywhere on earth

• more common than solar eclipse (the earth is larger than the moon, so has a larger shadow)

  

the geocentric universe

• the earth is the centre of the universe

• all celestial objects revolve around the earth

retrograde motion

• planets move from night to night relative to the stars

• the planets don’t follow a uniform pattern relative to the stars

• they appear to turn around relative to the stars

• this turn around is called ____ ____

cycles and epicycles

• the retrograde motion of the planets is inconsistent with planets moving in circles around the earth

• BUT, it is consistent with a “circles within circles” pattern, like a spirograph

Nicolaus Copernicus

• catholic canon/ scholar

• diplomat

• economist 

• translator

  • famous for:

  • the sun is the centre of the universe

  • planets orbit the sun in circles

  • the moon orbits the earth

apparent retrorade motion

• earth orbits faster than mars

• as earth passes mars, the position of mars on the sky, compared to background stars, changes

• this can explain the motion of the planets on the sky

Kepler’s first law

the orbit of each planet about the sun is an ellipse with the sun at one focus

Kepler’s second law

a planet moves faster in the part of its orbit nearer the sun and slower when farther from the sun, sweeping out equal areas in equal times

Kepler’s third law

more distant planets orbit the sun at slower average speeds, obeying a precise mathematical relationship

speed

the rate of change of position.

velocity

speed and direction

• car goes due north at 60 km/hour

acceleration

the rate of change of velocity

• speed change from 0km/h ro 100 km/h in 9s

newton’s first law

an object in motion remains in motion unless acted upon by an outside force

newton’s second law

acceleration is proportional to force and inversely proportional to mass

A=F/m

• more force means more acceleration

• more mass means less acceleration 

Newton’s third law

for every force, there is an equal and opposite reaction force

• shuttle is propelled upwards by a force equal and opposite to the force with which gas is propelled downwards

momentum

mass times velocity

p=mV

• if you add up the momentum of everything in a closed system, you will;l find that no matter what happens, this momentum is conserved

Angular momentum

mass times velocity times distance

w=mVr

if you add up the angular momentum of everything in a closed system you will find that no matter what happens, angular momentum is conserved 

newton’s universal law of gravitation

• there is a force between any 2 objects in the universe

• the force is proportional to the product of the masses of each object

• the force is inversely proportional to the square of the distance

• the force depends on M₁ times M₂

• if you double the mass of either object, you double the force

• if you half the mass of either object, you half the force

• the force depends on the distance between the centres of the 2 objects

• if you double the distance, you reduce the force by a factor 2×2=4

• if you half the distance, you increase the force by a factor of 2×2=4

freefall

why is the astronaut floating another not falling to earth?

• because he is in orbit, like his space craft

• when the only force acting on an object is gravity, we say you are in ______

Tidal Locking

friction with the rotating earth causes the tidal bulge to lag behind.

• this lag applies a force on the earth, causing its rotation to slow down

• the rotation period was 14 hours when the earth formed, now it is 24 hours

• the tidal force on the moon by the earth is much larger than the tidal force of the moon on the earth

  • so the moon has already stopped relative to earth

tides

the predictable, periodic rise and fall of sea levels caused by the gravitational forces of the Moon and Sun, which create bulges of water on Earth's surface

spring tide

in a full moon or a new moon, the tidal forces from the moon and the earth add

• happens when the sun, moon and earth are lined up. the moon can be on either side

• thee are the largest tides and 

• happen 2 times a month›

Neap Tide

in a quarter moon, the tidal forces from the sun partially cancel the tidal forces from the moon

• smallest tides of the month

• happens when the sun, moon, and earth are minimally lined up

why is the sunset red

because the sunlight must travel through more of the Earth's atmosphere, scattering away the shorter, blue wavelengths of light and leaving the longer, red and yellow wavelengths to reach our eyes

the sun

core → radiative zone → convective zone → photosphere

where does energy come from

• matter is made of atoms

• atoms stick to each other to form molecules

• a chemical reaction is a change in what molecules you have, the atoms stay the same

• some reactions, like burning natural gas give off energy 

helium atom

• 2 protons

• 2 neutrons

• 2 electrons

• the proton and neutron are in the nucleus 

• the electrons from a ‘cloud’ around the nucleus

• at high temperatures, the electrons are stripped away from the nucleus. This is called Plasma

Fusion in the Sun

if you can somehow combine 4 protons you get:

• 2 positrons (+ charged electrons)

• 2 neutrinos

• 2 gamma rays

• 1 helium nucleus

this has a lower mass than you started with

the remaining mass becomes energy, according to Einstein’s famous equation: E=mc²

• hard to do

• the + charge on the protons makes them repel each other

• they have to collide at very high speed to stick, or they will just bounce

pressure, temperature, and density

gas and plasma are made of particles

the particles are moving

• when they bounce off something, they apply pressure

• higher temperature: moving faster, higher pressure

• higher density: more particles, higher pressure

Hydrostatic Equilibrium in the sun - increased density

_____ ______ ‘equilibrium → rate of fusion increases → temperature increases → pressure increases → core expands → density drops → equilibrium restored

Hydrostatic Equilibrium in the sun - decreased density

_____ ____ ‘equilibrium’ → rate of fusion decreases → temperature decreases → pressure decreases → core contracts → density increases → equilibrium restored

Nuclear Fission

• ²³⁵U has 92 protons and 143 neutrons (235 total)

• if a slow neutron hits it, it forms ²³⁶U, which is unstable. the strong force can no longer hold it together

• it breaks up into smaller pieces

• the total mass of these smaller pieces is less than we started with

• the remaining mass converted to energy according to E=mc²

celestial equator

is an imaginary line that extends out from the Earth's Equator into the celestial sphere.

asteroid 

a rocky or metallic object that orbits the Sun, smaller than a planet but larger than a meteoroid