Unit 2: Gravitational Forces

Question 1

Describe the Stone-hedge in Southern England

Answer 1

• 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 )

Question 2

What did Ancient Babylon contribute to astronomy?

Answer 2

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

Question 3

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

Answer 3

• 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

Question 4

What is the real life distance between Syene and Alexandria

Answer 4

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)

Question 5

What did Eratosthenes find the earths circumference to be?

Answer 5

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

Question 6

What is Aristotle’s deductive reasoning for the earths curvature

Answer 6

• 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

Question 7

What is the geocentric system and who developed it

Answer 7

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

Question 8

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

Answer 8

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

Question 9

What is Direct motion in the geocentric model?

Answer 9

• planet moves eastward as seen from earth

- epicycle slowly eastward

Question 10

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

Answer 10

• 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

Question 11

Was Nicolaus Copernicus the first to present the heliocentric system?

Answer 11

• no

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

Question 12

What is the greatest elongation for Mercury and Venus?

- what are these planets also called

Answer 12

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

Question 13

What does Elongation mean?

Answer 13

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

Question 14

What is an angular degree?

Answer 14

1/360 part of a full circle

Question 15

What is an angular minute

Answer 15

1/60 part of a degree

Question 16

what is an angular second

Answer 16

1/60 part of a minute

Question 17

What is an angular diameter?

Answer 17

• the angle the object makes as seen by an observer

Question 18

What are the three measurements of angles?

Answer 18

• 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

Question 19

What is an Astronomical Unit

Answer 19

• the average distance between the earth and the sun

- 1 AU = 1.5x10^8 km

Question 20

What is the average distance between jupiter and the sun?

Answer 20

• 5.2 AU

Question 21

What is a light year?

Answer 21

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

- the distance that light travels in vacuum in one year

Question 22

What is a Parsec?

Answer 22

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

Question 23

What is an Arcsecond

Answer 23

• 1/3600 of a degree

Question 24

What is the Diameter of the milk way

Answer 24

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

Question 25

What is the Parallax | - Who invented it

Answer 25

- 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

Question 26

What star did Tycho unexpectedly observe

Answer 26

- 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

Question 27

What is Observational Astronomy - who influenced it - what was his observations on

Answer 27

- 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

Question 28

Who is Johannes Kepler

Answer 28

- from prague - he believed that planet's orbit was perfectly circular - created 3 laws of planetary motion

Question 29

What is Johannes Keplers First law of planetary motion

Answer 29

- 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)

Question 30

What is Johannes Keplers second law of planetary motion

Answer 30

- 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)

Question 31

What is Johannes Keplers third law of planetary motion

Answer 31

- 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

Question 32

What was the significance of Galileo?

Answer 32

- 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)

Question 33

How many stars can be seen by the naked eye

Answer 33

- 3000-5000 stars can be seen by the naked eye

Question 34

Who was the first to report lunar mountains and craters?

Answer 34

- 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

Question 35

Who is Isaac Newton

Answer 35

- formulated three laws to describe the fundamental properties of physical reality

Question 36

What are Isaac Newtons Three laws of physical reality

Answer 36

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

Question 37

What is newtons law of universal gravitation | what is the gravitational force between two masses

Answer 37

- 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

Question 38

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

Answer 38

- it holds our planet in it's orbit despite a gigantic earth-sun distance of 1 AU

Question 39

Who is Edmund Halley

Answer 39

- he used newtons methods and predicted a comets return in 76 years and it happened

Question 40

Who is William Herschel | what did he find out 50 years later

Answer 40

- discovered the 7th planet URANUS in 1781 | - 50 years later he found out that uranus was not following the orbit predicted by Newton laws