Unit 2: Gravitational Forces Flashcards
Describe the Stone-hedge in Southern England
- one of the oldest and largest observatories
- 30 basic stones 5.5 m high
- 29.5 m diameter
- heel stone: marks the position of summer solstice (not anymore though because of the precessions of the earths orbital axis )
What did Ancient Babylon contribute to astronomy?
- tablet containing important astronomical digest
- they developed precise mathematical formulas for predicting some astronomical events like lunar phases
- In mesopotamia
What is the Aztecs Calendar
Whats another name for it
whats the diameter
when was it discovered
- called the Sun Stone
- 3.7 meters diameter and 24 tons
- discovered in 1790 in mexico
- the base is a 52 year circle (same as our century)
- an Aztecs year consists of 18 months and 20 days each with 5 unhappy days at the end of the year
What is the real life distance between Syene and Alexandria
about 5000 stadiums
- the angle of 7degree 12’ is 1/50th part of circle
therefore the earths circumference is 50 times longer than Syene-Alexandria distance
(zenith at each created the angle)
What did Eratosthenes find the earths circumference to be?
- 252,000 stadiums
- 39,690km
(modern earth circumference is 40,074km so very close to Eratosthenes prediction)
What is Aristotle’s deductive reasoning for the earths curvature
- that the earth is spherical not flat
- the curvature of the earths shadow on the moon, only a spherical body can cast a circular shadow for all alignment of the sun ,moon and earth
What is the geocentric system and who developed it
- the belief that everything revolved around the earth
- planets were wandering stars
- Claudius ptolemy
what is the retrograde motion in the geocentric model ? (the path of mars)
- as seen from earth the planet moves rapidly westward along epicycle
- epicycle moves slowly eastward along deferent
- planet on inside of deferent
What is Direct motion in the geocentric model?
- planet moves eastward as seen from earth
- epicycle slowly eastward
What is the heliocentric model
Who developed it
what did it find a natural explanation for
- developed by Nicolaus Copernicus
- sun -centered model of the solar system
- in this model the retrograde motion (mars path) found natural explanation
- the earth overtakes and passes the slower moving planet of mars
Was Nicolaus Copernicus the first to present the heliocentric system?
- no
- greek scientist Aristarchus of Samos, and an indian mathematician and astronomer ayra-bhatta
What is the greatest elongation for Mercury and Venus?
- what are these planets also called
- between 18 and 28 degrees for mercury
- between 45 and 47 degrees for venus
- also called the morning and evening stars
What does Elongation mean?
- the angular distance in celestial longitude separating moon or planet from the sun
What is an angular degree?
1/360 part of a full circle
What is an angular minute
1/60 part of a degree
what is an angular second
1/60 part of a minute
What is an angular diameter?
- the angle the object makes as seen by an observer
What are the three measurements of angles?
- Sextant (can measure an angle on any plane)
- Astrolabe (only measures angles in a vertical plane, used in latitude finding
- A jacobs staff (used for supporting compass or instrument, single rod
What is an Astronomical Unit
- the average distance between the earth and the sun
- 1 AU = 1.5x10^8 km
What is the average distance between jupiter and the sun?
- 5.2 AU
What is a light year?
- 1 Iy=9.46x10^12km or aprox 63,000 AU
- the distance that light travels in vacuum in one year
What is a Parsec?
- 1 parsec is the distance at which 1 AU makes an angle of 1 arcsecond
- approx 3.26 ly
What is an Arcsecond
- 1/3600 of a degree
What is the Diameter of the milk way
- 100,000 Light years (one way )
or
9.25x10^17km
What is the Parallax
- Who invented it
- tycho brahe and johannes kepler
- the apparent change in the location of an object due to the difference in the location of the observer
- where two parallel views cross paths
What star did Tycho unexpectedly observe
- SN 1572
- it unexpectedly appeared in the sky because the parallax of the star was too small to measure
- this means the heavens is not unchangeable
- 8000 to 9000 light years away
What is Observational Astronomy
- who influenced it
- what was his observations on
- Tychos observations of planetary positions were astonishing both in their accuracy and quality
- his data was much more accurate than any other of his time
- tycho was the last major astronomer who worked without a telescope
Who is Johannes Kepler
- from prague
- he believed that planet’s orbit was perfectly circular
- created 3 laws of planetary motion
What is Johannes Keplers First law of planetary motion
- the orbit of a planet around the sun is an ellipse with the sun at one focus
- the law of orbits
- the amount of elongation in a planet’s orbit is defined as its orbital eccentricity
(less than zero means squished circle)
What is Johannes Keplers second law of planetary motion
- a line joining the planet and the sun sweeps out equal areas in equal intervals of time
- planet moves faster when closer to the sun (perihelion) and slower when farther from the sun (aphelion)
What is Johannes Keplers third law of planetary motion
- the square of a planets period around the sun is directly proportional to the cube of it semi-major axis (orbital radius)
- T^2 = a^3
What was the significance of Galileo?
- he was the first to use a telescope to examine celestial objects
- his findings supported a heliocentric model of the solar system
- called it a “spy glass”
- he discovered that venus, like the moon, undergoes a series of phases
- he also discovered moons in orbit around the planet of Jupiter
(galileo moons, 4 of them)
How many stars can be seen by the naked eye
- 3000-5000 stars can be seen by the naked eye
Who was the first to report lunar mountains and craters?
- Galileo
- this led him to the conclusions that the moon was “rough and uneven and just like the surface of the earth itself” rather than a perfect sphere as Aristotle had claimed
Who is Isaac Newton
- formulated three laws to describe the fundamental properties of physical reality
What are Isaac Newtons Three laws of physical reality
- law of Inertia (mass)
- a= F/m (Acceleration)
- Action - reaction
- these were applied to other objects in the solar system not just planets
What is newtons law of universal gravitation
what is the gravitational force between two masses
- two objects attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
- the gravitational force between two masses is as small as the weight of a .03mg dust speck gravitational force
What does the gravitational force between the earth and the sun do?
- it holds our planet in it’s orbit despite a gigantic earth-sun distance of 1 AU
Who is Edmund Halley
- he used newtons methods and predicted a comets return in 76 years and it happened
Who is William Herschel
what did he find out 50 years later
- discovered the 7th planet URANUS in 1781
- 50 years later he found out that uranus was not following the orbit predicted by Newton laws
