lOMoARcPSD|24365327
LECTURE 1
Chap 0 Pt1 (CELESTIAL SPHERE, RA AND DEC, ECLIPTIC/ZODIAC, SEASONS,
CONSTELLATIONS, LUNAR PHASES, ORIENTATION OF MOON/EARTH/SUN)
- Astronomy: Study of the universe (sun, planets, stars, galaxies etc.)
- Earth is in: The Local Supercluster -> The Local Group (group of galaxies) -> Milky Way
Galaxy -> Solar System
- Moon is 240,000 miles away
- 80 MPH it would take 4 months to get there
- Tesla ‘starman’ is currently “driving” at 17,276 mph so it will take about 13 hours
- SUn is 93 million miles away (130 years at 80mph)
- Distance to nearest star is 2x10^13 miles (100,000 years for starman)
- Nearest star isn't very accessible
- Size of galaxy: 2x10^17 miles (10000 times greater)
- Distance to closest galaxy (Andromeda): 2x10^19 miles (100 times greater)
- Scale model of universe:
- If the earth were the size of a eraser tip
- 1 foot away
- Sun is 125 yards
- Nearest star is 16000 miles away
- Distance Units in Astronomy:
- 1 m (meter) = 1 yard
- 1 km (kilometer) = 10^3 m = .62 miles
- 1 AU (astronomical unit) = distance to sun = 93,000,000 miles
- 1 light year = distance traveled by light in 1 year = 10^12 km
- (speed of light = 3 x 10^5 km/s = 186,000 miles)
- Light years:
- Moon light takes 1.5 seconds to reach earth
- Sunlight takes 8 minutes
- Nearest stars light takes 4 years
- Center of galaxy light takes 26,000 years
- Andromeda galaxy takes 2 million years
- Our study f the universe begins by examining the sky: stars, planets, sun, moon
- Constellations are random configurations of stars (orion, dippers)
- 3 stars = orion's belt
- All stars are actually different distances
- Constellations appear to move across the sky at night because Earth spins on its axis
- The Celestial Sphere:
- Stars appear to be attached to a giant “ceiling” extended around Earth moving East to
West
- Earth’s rotation axis intersects the Celestial Sphere at the North and South Celestial poles
Chapter 0 Pt 2
- We think in terms of degrees for distance from planets/stars
- Celestial Coordinates:
- Declination - angle in degrees above/below Celestial equator
, lOMoARcPSD|24365327
- Similar to Latitude on Earth (0 Dec at celestial equator)
- Right Ascension - time to rotate through a given angle (measured in hours-minutes-
seconds)
- similar to longitude on earth (0 RA at position where celestial equator crosses
ecliptic)
- Earth rotates on axis once per day
- Earth orbits sun once every year
- Solar day - 24 hours (one rotation relative to sun)
- Sidereal Day - 23 hr 56 min (one rotation relative to stars)
- The path that the Sun, Moon, and Planets follow through the constellations is the ecliptic
- Over the course of a year, the dark side of Earth faces different directions in the sky ->
we see different stars and constellations in the night sky during different months
- The Zodiac belt is the set of constellations that happen to lie in the plane of the Earth’s
orbit around the sun
- Ecliptic plane is tilted 23.5 degrees from Earth’s rotational axis
- TIlted axis is responsible for seasons
- Colder temps in winter are a result of:
- Sun stays lower in the sky during day
- Sun is above horizon for short periods (short days)
- The moon played important role in ancient astronomy
- Calendars and religious observances were tied to its phases and cycles
- Our calendar is based on lunar orbit
- Lunar Phases:
- Moon only emits reflected light from the sun
- Lunar eclipse:
- Earth blocks the sun's light from the moon
- Can be seen from anywhere on earth where the moon is visible
- A total lunar eclipse occurs during the fool moon phase
- Solar Eclipse:
- Moon blocks sunlight from earth
- Moon and sun have same angular size on sky
- Can only be seen from specific places on earth
- Solar eclipse occur at new moon
- Lunar eclipse occur at full moon
- Why don't we see eclipses every month?:
- Moons orbital plane is tilted 5 degrees to the ecliptic plane
- Eclipses occur only when moon crosses ecliptic when its a full moon
- Partial total, or annular solar eclipse occurs some place on earth between 3 and 5
times a year
, lOMoARcPSD|24365327
Chapter 1: The Copernican Revolution (RETROGRADE, PTOLEMY,COPERN, GALILEO, ETC,
GEOCENTRIC/HELIOCENTRIC, KEPLERS/NEWTONS LAWS/EQUATIONS)
- The sun, moon, and stars all move smoothly across the sky
- Slight changes in brightness and positioning happening
- Early observers noticed that 5 bodies called planets move differently (They move in 2 ways);
- Direct Motion - normal eastward movement
- Retrograde Motion - occasional westward movement… causing planet to appear making
“loops”
- The Geocentric Models:
- Followed Greek philosopher Aristotle
- Earth at center with plantes/sun orbiting circular
- Explain planetary motions using deferents and epicycle
- Ptolemaic Universe
- Useful for predicting positions of planets in sky (but ultimately wrong)
- Nicholas Copernicus (1473-1543)
- Introduced mathematical model for Heliocentric Universe
- Earth spins on axis
- STILL circular orbits
- Earth and all planets orbit the sun
- Only moon orbits Earth
- Retrograde motion is an optical illusion
- A planet appears to undergo retrograde motion when the Earth approaches and
overtakes that planet in its orbit
- Galileo Galilei
- Father of experimental science
- First to point telescope to sky in 1609 (he built it)
- Discoveries:
- Moon craters
, lOMoARcPSD|24365327
- Sunspots
- Moons of jupiter
- Phases of venus
- Scientific Method: Observation->Explanation->Prediction
- The Laws of Planetary Motion:
- Tycho Brahe (1546-1601) - Danish astronomer
- Recorded superb naked eye positions of planets
- Became an employer of Kepler who inherited all of his data
- Johannes Kepler (1571-1630) - German Mathematician/Astronomer
- Used Brahe’s data to describe shapes and speeds of planetary orbits
- Produced a theoretically derived heliocentric model that matched data
- Planets on elliptical orbits NOT circular
- Kepler’s Laws:
- FIRST LAW: Planetary orbits are ellipses, with the sun at one focus
- Eccentricity = major axis- minor axis
------------------------------
major Axis
- Describes moon and all orbiting bodies
- SECOND LAW: Planets sweep out equal areas in equal intervals of time
- They move fastest at perihelion(closer to sun) and slowest at aphelion (farther
away from sun)
- THIRD LAW: The square of a planet’s orbital period is proportional to the cube of its
semi-major axis
- P^2 = a^3
- P = Period (years) = Time for one orbit
- Semi major (a in AU) = average distance (radius if circular)
- P(period)^2 = a(semi-major axis)^3
- Isacc Newton - 17th century british mathematician
- Developed Newtonian Mechanics
- 3 laws of motion/gravity/calculus sufficiently explains virtually all motion
- Only in extreme cases do these laws of motion break down
- NEWTON'S LAWS:
- FIRST: A body in motion or at rest will stay that way until some
external force changes it
- SECOND: The acceleration of an object is directly proportional
to the applied force and inversely proportional to the object's
mass
- Force = mass x acceleration
- Two objects piled with same force causes one with
greater mass to accelerate less
- THIRD: Whenever one body exerts a force a force on a second
body exerts an equal and opposite force on the first OR For
every action there is an equal and opposite reaction
LECTURE 1
Chap 0 Pt1 (CELESTIAL SPHERE, RA AND DEC, ECLIPTIC/ZODIAC, SEASONS,
CONSTELLATIONS, LUNAR PHASES, ORIENTATION OF MOON/EARTH/SUN)
- Astronomy: Study of the universe (sun, planets, stars, galaxies etc.)
- Earth is in: The Local Supercluster -> The Local Group (group of galaxies) -> Milky Way
Galaxy -> Solar System
- Moon is 240,000 miles away
- 80 MPH it would take 4 months to get there
- Tesla ‘starman’ is currently “driving” at 17,276 mph so it will take about 13 hours
- SUn is 93 million miles away (130 years at 80mph)
- Distance to nearest star is 2x10^13 miles (100,000 years for starman)
- Nearest star isn't very accessible
- Size of galaxy: 2x10^17 miles (10000 times greater)
- Distance to closest galaxy (Andromeda): 2x10^19 miles (100 times greater)
- Scale model of universe:
- If the earth were the size of a eraser tip
- 1 foot away
- Sun is 125 yards
- Nearest star is 16000 miles away
- Distance Units in Astronomy:
- 1 m (meter) = 1 yard
- 1 km (kilometer) = 10^3 m = .62 miles
- 1 AU (astronomical unit) = distance to sun = 93,000,000 miles
- 1 light year = distance traveled by light in 1 year = 10^12 km
- (speed of light = 3 x 10^5 km/s = 186,000 miles)
- Light years:
- Moon light takes 1.5 seconds to reach earth
- Sunlight takes 8 minutes
- Nearest stars light takes 4 years
- Center of galaxy light takes 26,000 years
- Andromeda galaxy takes 2 million years
- Our study f the universe begins by examining the sky: stars, planets, sun, moon
- Constellations are random configurations of stars (orion, dippers)
- 3 stars = orion's belt
- All stars are actually different distances
- Constellations appear to move across the sky at night because Earth spins on its axis
- The Celestial Sphere:
- Stars appear to be attached to a giant “ceiling” extended around Earth moving East to
West
- Earth’s rotation axis intersects the Celestial Sphere at the North and South Celestial poles
Chapter 0 Pt 2
- We think in terms of degrees for distance from planets/stars
- Celestial Coordinates:
- Declination - angle in degrees above/below Celestial equator
, lOMoARcPSD|24365327
- Similar to Latitude on Earth (0 Dec at celestial equator)
- Right Ascension - time to rotate through a given angle (measured in hours-minutes-
seconds)
- similar to longitude on earth (0 RA at position where celestial equator crosses
ecliptic)
- Earth rotates on axis once per day
- Earth orbits sun once every year
- Solar day - 24 hours (one rotation relative to sun)
- Sidereal Day - 23 hr 56 min (one rotation relative to stars)
- The path that the Sun, Moon, and Planets follow through the constellations is the ecliptic
- Over the course of a year, the dark side of Earth faces different directions in the sky ->
we see different stars and constellations in the night sky during different months
- The Zodiac belt is the set of constellations that happen to lie in the plane of the Earth’s
orbit around the sun
- Ecliptic plane is tilted 23.5 degrees from Earth’s rotational axis
- TIlted axis is responsible for seasons
- Colder temps in winter are a result of:
- Sun stays lower in the sky during day
- Sun is above horizon for short periods (short days)
- The moon played important role in ancient astronomy
- Calendars and religious observances were tied to its phases and cycles
- Our calendar is based on lunar orbit
- Lunar Phases:
- Moon only emits reflected light from the sun
- Lunar eclipse:
- Earth blocks the sun's light from the moon
- Can be seen from anywhere on earth where the moon is visible
- A total lunar eclipse occurs during the fool moon phase
- Solar Eclipse:
- Moon blocks sunlight from earth
- Moon and sun have same angular size on sky
- Can only be seen from specific places on earth
- Solar eclipse occur at new moon
- Lunar eclipse occur at full moon
- Why don't we see eclipses every month?:
- Moons orbital plane is tilted 5 degrees to the ecliptic plane
- Eclipses occur only when moon crosses ecliptic when its a full moon
- Partial total, or annular solar eclipse occurs some place on earth between 3 and 5
times a year
, lOMoARcPSD|24365327
Chapter 1: The Copernican Revolution (RETROGRADE, PTOLEMY,COPERN, GALILEO, ETC,
GEOCENTRIC/HELIOCENTRIC, KEPLERS/NEWTONS LAWS/EQUATIONS)
- The sun, moon, and stars all move smoothly across the sky
- Slight changes in brightness and positioning happening
- Early observers noticed that 5 bodies called planets move differently (They move in 2 ways);
- Direct Motion - normal eastward movement
- Retrograde Motion - occasional westward movement… causing planet to appear making
“loops”
- The Geocentric Models:
- Followed Greek philosopher Aristotle
- Earth at center with plantes/sun orbiting circular
- Explain planetary motions using deferents and epicycle
- Ptolemaic Universe
- Useful for predicting positions of planets in sky (but ultimately wrong)
- Nicholas Copernicus (1473-1543)
- Introduced mathematical model for Heliocentric Universe
- Earth spins on axis
- STILL circular orbits
- Earth and all planets orbit the sun
- Only moon orbits Earth
- Retrograde motion is an optical illusion
- A planet appears to undergo retrograde motion when the Earth approaches and
overtakes that planet in its orbit
- Galileo Galilei
- Father of experimental science
- First to point telescope to sky in 1609 (he built it)
- Discoveries:
- Moon craters
, lOMoARcPSD|24365327
- Sunspots
- Moons of jupiter
- Phases of venus
- Scientific Method: Observation->Explanation->Prediction
- The Laws of Planetary Motion:
- Tycho Brahe (1546-1601) - Danish astronomer
- Recorded superb naked eye positions of planets
- Became an employer of Kepler who inherited all of his data
- Johannes Kepler (1571-1630) - German Mathematician/Astronomer
- Used Brahe’s data to describe shapes and speeds of planetary orbits
- Produced a theoretically derived heliocentric model that matched data
- Planets on elliptical orbits NOT circular
- Kepler’s Laws:
- FIRST LAW: Planetary orbits are ellipses, with the sun at one focus
- Eccentricity = major axis- minor axis
------------------------------
major Axis
- Describes moon and all orbiting bodies
- SECOND LAW: Planets sweep out equal areas in equal intervals of time
- They move fastest at perihelion(closer to sun) and slowest at aphelion (farther
away from sun)
- THIRD LAW: The square of a planet’s orbital period is proportional to the cube of its
semi-major axis
- P^2 = a^3
- P = Period (years) = Time for one orbit
- Semi major (a in AU) = average distance (radius if circular)
- P(period)^2 = a(semi-major axis)^3
- Isacc Newton - 17th century british mathematician
- Developed Newtonian Mechanics
- 3 laws of motion/gravity/calculus sufficiently explains virtually all motion
- Only in extreme cases do these laws of motion break down
- NEWTON'S LAWS:
- FIRST: A body in motion or at rest will stay that way until some
external force changes it
- SECOND: The acceleration of an object is directly proportional
to the applied force and inversely proportional to the object's
mass
- Force = mass x acceleration
- Two objects piled with same force causes one with
greater mass to accelerate less
- THIRD: Whenever one body exerts a force a force on a second
body exerts an equal and opposite force on the first OR For
every action there is an equal and opposite reaction
