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Astronomy > Unit 2: Gravitational Forces > Flashcards

Unit 2: Gravitational Forces Flashcards

1
Q

Describe the Stone-hedge in Southern England

A
  • 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 )
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2
Q

What did Ancient Babylon contribute to astronomy?

A
  • tablet containing important astronomical digest
  • they developed precise mathematical formulas for predicting some astronomical events like lunar phases
  • In mesopotamia
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3
Q

What is the Aztecs Calendar
Whats another name for it
whats the diameter
when was it discovered

A
  • 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
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4
Q

What is the real life distance between Syene and Alexandria

A

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)

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5
Q

What did Eratosthenes find the earths circumference to be?

A
  • 252,000 stadiums
  • 39,690km
    (modern earth circumference is 40,074km so very close to Eratosthenes prediction)
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6
Q

What is Aristotle’s deductive reasoning for the earths curvature

A
  • 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
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7
Q

What is the geocentric system and who developed it

A
  • the belief that everything revolved around the earth
  • planets were wandering stars
  • Claudius ptolemy
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8
Q

what is the retrograde motion in the geocentric model ? (the path of mars)

A
  • as seen from earth the planet moves rapidly westward along epicycle
  • epicycle moves slowly eastward along deferent
  • planet on inside of deferent
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9
Q

What is Direct motion in the geocentric model?

A
  • planet moves eastward as seen from earth

- epicycle slowly eastward

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10
Q

What is the heliocentric model
Who developed it
what did it find a natural explanation for

A
  • 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
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11
Q

Was Nicolaus Copernicus the first to present the heliocentric system?

A
  • no

- greek scientist Aristarchus of Samos, and an indian mathematician and astronomer ayra-bhatta

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12
Q

What is the greatest elongation for Mercury and Venus?

- what are these planets also called

A
  • between 18 and 28 degrees for mercury
  • between 45 and 47 degrees for venus
  • also called the morning and evening stars
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13
Q

What does Elongation mean?

A
  • the angular distance in celestial longitude separating moon or planet from the sun
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14
Q

What is an angular degree?

A

1/360 part of a full circle

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15
Q

What is an angular minute

A

1/60 part of a degree

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16
Q

what is an angular second

A

1/60 part of a minute

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17
Q

What is an angular diameter?

A
  • the angle the object makes as seen by an observer
18
Q

What are the three measurements of angles?

A
  • 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
19
Q

What is an Astronomical Unit

A
  • the average distance between the earth and the sun

- 1 AU = 1.5x10^8 km

20
Q

What is the average distance between jupiter and the sun?

A
  • 5.2 AU
21
Q

What is a light year?

A
  • 1 Iy=9.46x10^12km or aprox 63,000 AU

- the distance that light travels in vacuum in one year

22
Q

What is a Parsec?

A
  • 1 parsec is the distance at which 1 AU makes an angle of 1 arcsecond
  • approx 3.26 ly
23
Q

What is an Arcsecond

A
  • 1/3600 of a degree
24
Q

What is the Diameter of the milk way

A
  • 100,000 Light years (one way )
    or
    9.25x10^17km
25
Q

What is the Parallax

- Who invented it

A
  • 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
26
Q

What star did Tycho unexpectedly observe

A
  • 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
27
Q

What is Observational Astronomy

  • who influenced it
  • what was his observations on
A
  • 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
28
Q

Who is Johannes Kepler

A
  • from prague
  • he believed that planet’s orbit was perfectly circular
  • created 3 laws of planetary motion
29
Q

What is Johannes Keplers First law of planetary motion

A
  • 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)
30
Q

What is Johannes Keplers second law of planetary motion

A
  • 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)
31
Q

What is Johannes Keplers third law of planetary motion

A
  • 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
32
Q

What was the significance of Galileo?

A
  • 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)
33
Q

How many stars can be seen by the naked eye

A
  • 3000-5000 stars can be seen by the naked eye
34
Q

Who was the first to report lunar mountains and craters?

A
  • 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
35
Q

Who is Isaac Newton

A
  • formulated three laws to describe the fundamental properties of physical reality
36
Q

What are Isaac Newtons Three laws of physical reality

A
  1. law of Inertia (mass)
  2. a= F/m (Acceleration)
  3. Action - reaction
    - these were applied to other objects in the solar system not just planets
37
Q

What is newtons law of universal gravitation

what is the gravitational force between two masses

A
  • 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
38
Q

What does the gravitational force between the earth and the sun do?

A
  • it holds our planet in it’s orbit despite a gigantic earth-sun distance of 1 AU
39
Q

Who is Edmund Halley

A
  • he used newtons methods and predicted a comets return in 76 years and it happened
40
Q

Who is William Herschel

what did he find out 50 years later

A
  • discovered the 7th planet URANUS in 1781

- 50 years later he found out that uranus was not following the orbit predicted by Newton laws

Astronomy (10 decks)

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