AST101

Midterm 1 material

The order of the solar system

Sun → Mercury → Venus → Earth → Mars → Jupiter → Saturn → Uranus → Neptune

Explain planets’ orbit movement

• the planets all orbit in the same plane - ecliptic plane

• the planets all orbit the same direction

• the sun rotates in the same direction that planets orbit

• the planets all have elliptic orbits

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

Describe characteristics of Mercury

• closest planet to the Sun

• no atmosphere

• highly cratered surface

• rocky exterior with a huge iron core

• temperature fluctuates between -170C and 425C 

• no moons

Describe characteristics of Venus

• about the same size as Earth

• has lots of volcanoes

• thick CO2 atmosphere

• runaway greenhouse effect makes it even hotter than Mercury

• temperature is constant at 460C

• it rains acid

• no moons

• rotates very slowly and backwards

Describe characteristics of Earth

• about the same size as Venus

• lots of volcanoes

• O2+N2 atmosphere

• large oceans regulate CO2

• surface heavily effected by life

• has 1 large moon

• 23.4 degree orbital tilt produces significant seasons

Describe characteristics of Mars

• lots of extinct volcanoes

• very thin CO2 atmosphere

• oceans have evaporated

• no evidence for life

• has 2 small moons

• polar ice/dry-ice caps

• planet wide dust storms

• 25.2 degree orbital tilt produces significant

What are terrestrial planets?

These are Mercury, Venus, Earth & Mars. They are

• small

• rocky

• relatively thin or no atmosphere

• have few moons

• made from heavy elements

Describe characteristics of 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 known to date

Describe characteristics of Saturn

• second largest planet in the solar system

• structure is similar to Jupiter

• has spectacular rings

• has more than 60 moons

Describe characteristics of Uranus

• coldest planet

• small rocky core

• thick water + ammonia + methane mantle

• thick H2/He atmosphere

• rotation axis tilted 98 degrees

• thin rings and lots of moons

Describe characteristics of Neptune

• furthest planet from the Sun

• structure very similar to Uranus

• rotation axis tilted 28 degree

• more surface features than Uranus

• strongest winds in the solar system: up to 2,100 km/h

What are Jovian planets?

These are Jupiter, Saturn, Uranus, Neptune. They are

• large

• contain gas + liquid

• have many moons

• mostly light elements

Describe season of summer in terms of Sun & rotation

during Summer,

• daylight is longer & darkness is shorter

• Sun gets ‘higher’ in the sky so sunlight is more direct & Earth is hotter

Describe season of winter in terms of Sun & rotation

In winter,

• daylight is shorter and darkness is longer

• sun does not get as ‘high’ in the sky, so sunlight is at an angle & Earth is colder

Describe how Sun shines on Northern and Southern hemispheres throughout different times of the year.

What does the phase of the moon depend on?

It depends on where the Moon is compared to the Sun

Describe this moon phase

New Moon

• when the moon is in the direction of the sun

• the only time a Solar eclipse can happen (when the Moon blocks the Sun)

• Unlit side faces the Earth

• rises with the Sun and sets with the Sun

• not generally visible on Earth

Describe this moon phase.

Waxing Crescent

• happens 3-4 days after the new moon

• rises around 3h after the Sun (9am)

• sets around 3h after the Sun (evening-early night)

• easiest to see right after sunset

Describe this moon phase.

Waxing Quarter

• 1 week after the new moon

• moon is lit from the side

• rises around 6h after the sun (12pm)

• sets around 6 hours after the sun (midnight or later)

• easiest to see at night before midnight

Describe this moon phase.

Waxing Gibbous

• 10-11 days after the new moon.

• rises around 9h after the Sun (3pm)

• sets around 9h after the Sun (night)

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

Describe this moon phase.

Full Moon

• two weeks after the new moon

• the only time a Lunar eclipse can happen (moon enters Earth’s shadow)

• rises around 12h after the sun rises (5pm)

• sets around 12h after the sun sets (closer to sunrise)

• visible most of the night

Describe this moon phase.

Waning Gibbous

• 10-11 days before the next new moon

• rises around 3h after the sun sets (9pmish)

• sets around 3h after the sun rises (in the morning)

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

Describe this moon phase.

Waning Quarter

• around a week before the next new moon

• rises around 6h before the sun rises (midnight)

• sets around 6 hours before the sun sets (afternoon)

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

Describe this moon phase.

Waning Crescent.

• 2-4 days before the next new moon

• rises around 3h before the sun rises (late night)

• sets around 3h before the sun sets(early evening)

• easiest to see before sunrise.

Describe process of Solar Eclipse

It’s when the Moon blocks light from the Sun to Earth. Happens when the New Moon crosses the ecliptic plane.

It only casts a shadow on a small part of the Earth

Why does Solar Eclipse happen rarely?

Since the Moon’s orbit is tipped relative to the ecliptic plane.

Describe the process of Lunar Eclipse

It happens when the Moon enters the Earth’s shadow. It’s when a full moon crosses the ecliptic plane. It’s more common than a Solar Eclipse since Earth has a bigger shadow.

What is Geocentric Universe?

In Geocentric model of the Universe, the Earth is the centre of it. All celestial objects revolve around the Earth

What is Retrograde Motion?

Retrograde motion is planets turning around relative to the stars.

What is Nicolaus Copernicus’ idea of the Universe? (1473-1543)

Copernicus suggested that Sun is the center of the Universe and planets orbit in circles around it. He also suggested that moon orbits the Earth.

He also explain Retrograde motion - he observed that 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

What are Tycho Brahe’s (1546-1601) contributions to astronomy?

He made extremely precise measurements of the motion of Mars

Observed a SuperNova

Used parallax to constrain distances

From his data, current models clearly had problems

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.

T=365.24 sqrt root r³. T - orbital period in days; r - orbital radius in AU; 1 AU is the radius of the earth’s orbit

What did Galileo Galilei discover?

He developed and used telescopes; experimented with laws of motion & gravity. Using telescopes, he discovered that:

• the moon has craters

• Jupiter has moons that orbit it so not everything revolves the Earth

• Venus has phases

What are phases of Venus?

Galileo discovered that the apparent size of Venus changes throughout the year. The ‘new’ phase happens when Venus appears largest. the ‘full’ phase’ happens when Venus is in line with the Sun and when it appears the smallest.

Newton’s First Law

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

Newton’s Second Law

Acceleration is proportional to Force and inversely proportional to mass/

A=F/m

F=mA

More Force → more acceleration

More Mass → less acceleration 

Newton’s Third Law

For every force, there is always an equal and opposite reaction force.

What is momentum? what about angular momentum?

p=mV. Mass times Velocty

Angular momentum is mass times velocity times distance (w=mVr).

Momentum is always conserved

Newton’s Universal Law of Gravitation

F = (G M1M2) / d²

There is a force between any two objects in the Universe. It’s proportional to the product of the masses of each object & inversely proportional to the square of the distance

Escape velocity

Escape velocity is the minimum speed an object must attain to overcome the gravitational pull of a celestial body, such as a planet, and move away indefinitely without additional propulsion.

Freefall

State of object when the only force acting on it is gravity

How do tides happen?

Tides happen due to varying gravitational force squeezing both the Earth and the Moon.

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.

What is Spring tide?

In a full moon or new moon, the tidal forces from the Moon and the Earth add. It happens when the Sun, Moon, and Earth are lined up - Moon can be on either side.
These are the largest tides and happen twice per month - at new moon and full moon.

What is Neap Tide?

In a quarter moon, the tidal forces from the Sun partially cancel the tidal forces from the moon. It happens when the Sun, Moon, and Earth are minimally lined up. These are the smallest tides and happen at the quarter moons.

What are metrics of the Earth and the Sun?

Why is the sunset red?

Sun is actually white and radiates all colors. We see red Sun because atmosphere scatters blue light and red light makes it through the atmosphere unscattered.

Describe structure of the Sun

What is fusion?

Fusion is process of combining 4 protons. By doing this you can get

• 2 positrons

• 2 neutrinos

• 2 gamma rays

• 1 helium nucleus.

This has lower mass then what you started with. The remaining mass becomes energy - so fusion releases a lot of energy

Why is fusion hard?

Fusion is hard because protons have positive charge - so they repel each other. Unless the speeds are really high, the protons push apart when they get close and don’t collide.

What makes fusion possible?

High temperature → high speed. It needs to be millions of degrees for fusion to happen, as well as very high density.

Describe the processes of reaching hydrostatic equilibrium in the Sun

1. Density above equilibrium → rate of fusion increases → temperature increases → pressure increases → core expands → density drops → equilibrium restored.

2. Density below equilibrium → rate of fusion decreases → temperature decreases → pressure decreases → core contracts → density increases → equilibrium restored

How does fission happen?

If a slow neutron hits a molecule, it forms a new element which is unstable. The strong force can no longer hold it together - so it breaks up into smaller pieces. The total mass of these smaller pieces is less than before so remaining mass is converted to energy.

Where are Nuclear fission and Nuclear fusion used in?

Nuclear Fission: nuclear power plants, small nuclear bombs

Nuclear Fusion: thermonuclear bombs (hydrogen bombs)

Describe core of the Sun

In core of the Sun, fusion takes place.

It’s around 10 Million C.

It’s over 100 times density of water.

Describe Radiative Zone of the Sun

It’s hot but calm.

A few million C so now fusion takes place here.

Around the density of water

Describe Convection Zone of the Sun

Hot plasma rises, bring heat to surface. It also has bright and dark regions because of plasma rising and sinking when cooling. This creates Sunspots - cooler spots on the Sun

Hundreds of thousands of C

Density of styrofoam