Earth and its Motions (Pres III)

Question 1

What are the two hierarchies of motion?

Answer 1

1) Diurnal Rotation - days & nights ( ~23h 56m 4s)

2) Annual Revolution - seasons ( ~365.25 days)

Question 2

What is Kepler’s 1st law?

Answer 2

Orbits of all planets are ellipses w/ sun located at foci of the ellipses

Question 3

Why are the orbits ellipses?

Answer 3

Because the planets are made of many different materials, the gravity is not uniform, resulting in elliptical orbits.
If the earth was made on a single material, the orbit would be spherical

Question 4

What is Kepler’s 2nd law?

Answer 4

The area swept out by the radius vector “r” is constant for a given time period. Remember elliptical drawing with shaded areas*
The areal vector is constant
Areal velocity: area of ellipse/period
Consequence: planets go faster when closer to the sun

Question 5

What is Kepler’s 3rd law?

Answer 5

The squares of the sidereal orbital periods of the planets are in direct proportion to the cubes of the semimajor axes of their orbits

Question 6

What is Newton’s First Law?

Answer 6

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force (Law of inertia)

Question 7

What is Newton’s Second Law?

Answer 7

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object

Question 8

What is Newton’s Third Law?

Answer 8

For every action, there is an equal and opposite reaction

action and reaction forces

Question 9

What is Newton’s Law of Universal Gravitation?

Answer 9

Every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them

Question 10

Why are Kepler’s Laws assumptions

Answer 10

Because they assume gravity is uniform, which is not true. Forces such as solar winds, air resistance, and gravity of other bodies affect the gravity field

Question 11

How much is Earth’s axis tilted

Answer 11

23.5 degrees

Question 12

What is the solar day?

Answer 12

Period of rotation about spin axis w/respect to the sun = 24 hours

Question 13

What is the sidereal day?

Answer 13

Period of rotation about spin axis w/respect to the fixed stars = 23h 56m 4.09s

Question 14

What is the solar period?

Answer 14

Time of orbital revolution of a planet with respect to the sun

Question 15

What is the sidereal period?

Answer 15

Time of orbital revolution of a planet with respect to the “fixed” stars

Question 16

What is the synodic period?

Answer 16

From the time celestial bodies align to the next time they align

Question 17

What is the solar year?

Answer 17

Period of orbital motion w/respect to the sun ~ 365 days, 5h, 48m, 45.51s

Question 18

What is the sidereal year?

Answer 18

Period of orbital motion w/respect to the fixed stars
~ 365.2564 … solar days
~ 366.2564 … sidereal days

Question 19

Ecliptic

Answer 19

The path of the Earth’s orbit

Question 20

Equinox

Answer 20

Direction in space coinciding with the intersection of the Earth’s equatorial plane with the ecliptic

Question 21

Solstice

Answer 21

Occasion when sun reaches the tropics
Summer solstice - tropic of cancer
Winter solstice - tropic of capricorn

Question 22

What is precession?

Answer 22

The Earth’s wobble

latin - forward shifting

Question 23

Who was instrumental in understanding precession?

Answer 23

Hipparchus - discovered in 2nd century BC
Copernicus - first ascribed as motion of axis
Newton - first explained properly

Question 24

Why does precession happen?

Answer 24

Because of the torque of unequal pull on the equatorial bulges of surrounding gravity bodies (sun, moon, planets)
If the earth was a sphere, the would be no precession

Question 25

What is the period of precession?

Answer 25

Platonic year ~25,765 years

Question 26

What are the requirements for precession?

Answer 26

1) Planet spinning on rotation axis in space
2) Source of gravitational attraction
3) Non-spherical shape
4) Inclination of equator to plane of orbit (obliquity of the ecliptic)

Question 27

What is Lunisolar Precession?

Answer 27

The moon is responsible for 2/3 of precessional motion

The sun is responsible for 1/3 of precessional motion

Question 28

Planetary precession

Answer 28

Other planet’s effect on precession

Question 29

General Precession

Answer 29

Lunisolar and planetary precession combined

Question 30

What are the season determined by?

Answer 30

Obliquity of orbit

Orbital period

Question 31

What has to be corrected for precession?

Answer 31

Calendar year

Question 32

What is nutation?

Answer 32

Periodic variations in precessional motion

Question 33

When was nutation discovered?

Answer 33

In 1747 by Bradley

Question 34

What 3 things cause it to happen?

Answer 34

1) Ellipticity of earth’s orbit
2) Ellipticity of moon’s orbit
3) Non-coincident of moon’s orbit w/ ecliptic inclination: 5 degrees 11 seconds

Question 35

What is the main period of nutation?

Answer 35

18.6 years

Question 36

What is the wobble of Polar Motion?

Answer 36

The push of the earth’s wobble against it’s crust, which causes changes in latitude

Question 37

What probably causes polar motion?

Answer 37

That the earth is not completely solid

Question 38

How long does polar motion take to complete a cycle?

Answer 38

~ 428 days

Question 39

Who calculated the mean position of the rotational pole?

Answer 39

The Conventional International Origin (CIO) in 1903-1905

Question 40

What is happening to the Length of the Day?

Answer 40

It’s changing slowly over time

Increased velocity = shorter day

Question 41

What is causes changes in day length

Answer 41

Interactions of atmosphere, oceans, winds, inner parts of earth being non-rigid