AST101 Midterm #1

Mercury

• Closest to sun (62.052 million km)

• No atmosphere

• No moons

• Rocky exterior with iron core

• Hot&cold temp,

Venus

• 2nd to Sun (107.52 million km)

• Similar size to Earth

• Thick CO2 atmosphere

• No moons

• Rotates backwards & slowly (days = long)

Earth

3rd to Sun (150.22 million km 1 light year), Similar size to Venus, O2 & N2 atmosphere, 23.4-degree rotational tilt.

Mars

4th to Sun (234.12 million km), No sign of life, Thin CO2 atmosphere, 2 small moons, Ice caps

Terrestrial Planets Summary

Closer to the Sun, Small, Rocky, Thin/no atmosphere, Heavier elements, Few moons, Faster orbits around the Sun

Jupiter

• 5th to the Sun (773.69 million km)

• Largest planet in solar system

• Thick gaseous atmosphere

• Non-visible rings

• Many moons

Saturn

• 6th to Sun (1.4282 billion km)

• 2nd largest planet

• Structure similar to Jupiter

• Visible rings

• Many moons

Uranus

• 7th to Sun (2.9173 billion km)

• Coldest planet

• Small rocky core

• Thick H2 & HE atmosphere

• Axial tilt 98 degrees

• Thin rings

• Lots of moons

Neptune

• 8th to Sun (4.4706 billion km)

• Furthest planet from the Sun,

• Structure similar to Uranus,

• Axial tilt 28 degrees,

• Has surface features,

• Strongest winds

Jovian Planets Summary

• Gas & Liquids

• Many moons

• Mainly light elements

• Slower orbit around the Sun.

The Moon’s Orbit

Tipped about 5 degrees in comparison to the Ecliptic Plane.

• This is what causes Eclipses to not be monthly. 

• Orbits in the same direction as the planets.

Dwarf Planets

Pluto, Ceres, Haumea, Quoar, Makemake, Gonggong, & Eris

• there could be hundreds more that are unidentified

Asteroid Belt

Surrounding the Terrestrial Planets (between Mars and Jupiter)

• A ring where most of the asteroids in our Solar System are found orbiting the Sun

• Total mass is around 3% of the Moon’s.

Kuiper Belt

Surrounds the Jovian & Terrestrial planets (beyond Neptune)

• A ring of asteroids, comets, and other icy bodies that orbit the sun beyond Neptune

• Includes several of the Dwarf Planets

Comets

Smaller icy bodies from the outer solar system, cosmic snowballs of frozen gases, rock, and dust that orbit the Sun

Earth’s Axial Tilt

• Tipped in relation to the orbital plane 23.4 degrees

  • The reason for the Seasons

Sun’s Rays

Impacted due to Earth’s axial tilt, the seasons are affected based on the directness of the sun’s rays. Steep angle = more direct & hotter, Shallow angle = less direct & colder

Ecliptic Plane

The imaginary plane containing the Earth’s orbit around the Sun

The Celestial Sphere

A model for the two-dimensional direction to the stars, sun and moon as viewed from a particular place on earth

Points on Celestial Sphere

Zenith (directly above an observer on Earth), Celestial Poles, Celestial Equator, Ecliptic

The Ecliptic

The apparent path of the Sun throughout the course of the year

Constellations

People mapped constellations (patterns) onto the stars, representing different things. They differ as the seasons change because the light changes (Ex: on Dec. 21, Sagittarius is the most visible constellation).

Moon Phases

Determined by which part of the Moon is illuminated from the Earth. The phase we see is dependent on where the Moon is compared to the Sun.

• Phases are best seen in the middle sections of their rising&setting times

Nodes

When the Moon passes the Ecliptic Plane at the right time, causing Eclipses. This happens about every six months.

New Moon

• When the Moon is lined up in front of the Sun/in the direction of the Sun

• Unlit side faces the Earth

• When Solar Eclipses can happen

• Rises 6AM and sets at 6PM

Waxing Crescent Moon

• Seeing mostly the dark side of the Moon

• Rises 9 AM, sets 9 PM

First Quarter / Waxing Quarter Moon

• A quarter of the way around it’s orbit

• Half Moon

• Rises 12 PM, sets 12 AM

Waxing Gibbous Moon

• Starting to get behind the Earth, so we are seeing more of the Moon

• Rises 3 PM, sets 3 AM

Full Moon

• Lunar Eclipse is possible

• Moon is behind the Earth, below the Ecliptic

• The Sun, Earth, and Moon are lined up

• Rises 6 PM, sets 6 AM

Waning Gibbous Moon

• Coming around the Earth now

• “Midnight” or “Late-night” Moon

• Rises 9 PM, sets 9 AM

3rd / Waning Quarter Moon

• Half Moon

• 3/4s around it’s orbit

• Rises 12 AM, sets 12 PM

Waning Crescent Moon

• Rare to see

• Rises 3 AM, sets 3 PM

Solar Eclipse

• Happens during a New Moon

• When the Moon blocks the light from the Sun

• Earth, Moon, Sun

• Happens only when the New Moon crosses the Ecliptic Plane (Node)

• Casts a shadow on a small part of the Earth (only a specific area/region will experience a full Solar Eclipse/full shadow)

Lunar Eclipse

• Happens during a Full Moon

• Blood Moon

• When the Moon enters the Earth’s Shadow

• Moon, Earth, Sun

• Happens only when a Full Moon crosses the Ecliptic Plane (Node)

• You can see it from everywhere on Earth

• More common than a Solar Eclipse

Pre-Copernicus

• Earth was the center of the Universe

• Everything revolves around the Earth in circles

Retrograde Motion

• Copernicus

• An illusion created when we observe other planets from the moving planet of Earth

• Backwards motion

• As Earth passes Mars, the position of Mars compared to the stars changes

• Used to explain the motion of the planets in the sky

• When Earth passes Mars, which means it’s moving faster, it happens

Copernicus

• New theory: Sun is the center of the Universe

• Apparent Retrograde Motion

  • Earth orbits faster than Mars, making it look like Mars is orbiting in the opposite direction

Tycho Brahe

• Precise measurements of Mars

• Parallax 

  • Measurement of distance to nearby stars

Kepler’s 1st Law

The orbit of each planet around the Sun is an ellipse with the Sun at one focus

Kepler’s 2nd Law

A planet moves faster in the part of its orbit nearer to the Sun and slower when farther from the Sun, sweeping out equal areas in equal times.

• Slower = further away from the Sun

• Faster = closer to the Sun

Kepler’s 3rd Law

More distant planets orbit the Sun at slower average speeds, obeying a precise mathematical relationship

• An equation that helps us predict each planet’s orbit

Geocentric Model

• Earth is the assumed center of the Universe

Heliocentric Model

• The Sun is at the center of the Universe

Epicycles

• Geocentric model

• Spirograph

• Circles within circles

Ellipses

• Heliocentric model

• The Sun’s center is always one focal point

• Describing a planet’s orbit about the Sun

• Makes it so that the planet’s distance to the Sun is constantly changing as the planet orbits around the Sun

Galileo Galilei

• Pioneer in telescopes

• Telescope → Moon has craters = Not everything in the heavens are perfect circles and spheres

• Telescope → Jupiter has moons = Earth is not the center of the Universe

• Telescope → Venus has phases = Venus is orbiting the Sun

Issac Newton

• Unified Physics and Astronomy

• Laws of Motion

  • Unified set of rules for both the Earth and the Heavens

• Universal Law of Gravitation

Speed

• The rate of change of position

  • e.g., The car is traveling 60km per hour

Velocity

• Speed & Direction

  • e.g., The car is traveling 60km per hour

Acceleration

• The rate of change of velocity, how quickly your velocity is changing

  • e.g., The car, traveling in a straight line, changes speed from 0km/hour to 100km/hour in 9s.

  • e.g., The car changes from going due north at 60km/hour to going due east at 60km/hour in 20s.

Newton’s First Law

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

• If there was no force, it wouldn’t stop

Newton’s Second Law

Acceleration is proportional to Force and inversely proportional to Mass

• Acceleration = Force divided by Mass

  • More force = more acceleration

  • More mass = less acceleration

• You apply a force, then you change either the direction or speed (acceleration)

Newton’s Third Law

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

• Jumping off a boat

  • You apply force to the boat, its reaction force pushes you to land, while the action force pushes the boat backwards.

Momentum

• Mass times Velocity (P = mV)

• Mass in motion 

• Dependent on how much stuff is moving (mass) and how fast the stuff is moving (velocity)

Angular Momentum

• Mass times Velocity times Distance

  • W = mVr

• Ex. Figure skater pulling in arms tight as they spin

  • Causes them to move faster while keeping the same total momentum

• Back to Kepler’s Laws — speed up when you’re closest, slow down when you’re farthest (Ellipses)

Newton’s Universal Law of Gravitation

• There is a force between any two objects in the Universe

• F = G x (M1M2/d2)

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

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

• The force is dependent on the distance between the two objects

  • If you double the distance, the force decreases and vice versa

Freefall

• No forces other than gravity are being applied

• The force of gravity equals the force you need to go in a circle/orbit around the earth without falling

Tides

Movement in the ocean due to the gravitational forces exerted by the Moon & Sun

• Happens twice a day

Earth’s Size/Shape Shift

• It gets squished, so there are tides on both sides

• Tides are deeper on the side away from the Moon and facing the Moon

Tidal Locking

• No matter when the Moon is observed from Earth, the same hemisphere of the Moon is always seen

  • Tides have slowed the spinning of the Moon down overtime so it has completely stopped

Tidal Lagging

• Due to friction with the rotating Earth

• They don’t happen at the highest point

• It then applies force to the Earth, causing its rotation to slow down over time

Spring Tide

• When the Moon, Earth, and Sun are all lined up (Full or New Moons)

• The forces of the Sun and Moon combine/work together, squishing the Earth x2

  • Creates the largest tides twice a month

Neap Tides

• During Quarter moons

• The Sun and Moon aren’t lined up, which means that their forces cancel each other/work against each other

  • The Moon wins

• Smallest tides twice a month

Moonrises

• 6 AM — New

• 9 AM — Crescent

• 12 PM — Quarter

• 3 PM — Gibbous

• 6 PM — Full

• 9 PM — Gibbous

• 12 AM — Quarter

• 3 AM — Crescent

Blue Light

• Atmosphere scatters it

• Makes you see a blue sky and a white sun when the sun is high

Red Light

• Makes it through the atmosphere unscattered

• When the Sun is low in the sky, it looks red/orange

Parts of the Sun

• The Core

• The Radiative Zone

• The Conective Zone

• Photosphere

• Corona

Nuclear Fusion

• Mass is converted into energy

• When two light atoms combine together

  • The remaining mass releases energy

Nuclear Fission

• Mass is converted into energy

• Splitting a heavy atom into two lighter atoms

  • The remaining mass is converted into energy

What the Sun is made up of

• Hot gas

  • 70% Hydrogen

  • 28% Helium

What keeps the Sun burning

• Nuclear Fusion

  • Fusing hydrogen atoms to make helium in its core

Ideal Gas Law

• Pressure

  • Gas & plasma are made of particles that bounce around, applying pressure

    • faster & more of them = more pressure

• Temperature

  • particles moving faster → higher pressure = Higher temperature

• Density

  • The more particles there are → higher pressure = Higher density

Hydrostatic Equilibrium in the Sun

1. Density is above equilibrium

2. The rate of Fusion then increases

3. Leads to temperature increase

4. The pressure then increases

5. So, the Core expands

6. Making the density drop

7. Equilibrium is restored

The Core

• Hottest part of the Sun (10 million C)

• Over 100 times the density of water

• Fusion takes place here

The Radiative Zone

• Hot but calm

  • No Fusion

• A few million C

• Around the density of water

The Convection Zone

• Hot plasma rises, bringing heat to the surface

• Hundreds of thousands of C

• Density of styrofoam

The Surface of the Sun

• Bright regions = Hot plasma rises from below

• Darker regions = Cooler plasma sinking

• This is convection

Sunspots

Cooler spots on the surface of the sun

• 11 year activity cycle