10 - the earth-moon-sun system ___1

Question 1

what did eratosthenes and aristarchus use to successfully determine the diameters of the earth, moon and sun and the distances to the moon and the sun

Answer 1

observations of the moon and sun

Question 2

what did eratosthenes and aristarchus successfully determine using observations of the moon and sun

Answer 2

diameters of the earth, moon and sun
the distances to the moon and the sun (from earth)

Question 3

story of eratosthenes

Answer 3

came to his attention that at noon on the summer solstice (june 21)
the sun lay directly over a deep well in the city of syene
+ there were no shadows cast by pillars at that time

these observations implied that the sun was directly overhead syene

Question 4

what was the state of alexandria at that same time

Answer 4

the sun was not directly overhead
vertical poles and column did cast a shadow

Question 5

what did eratosthenes sought to do

Answer 5

use such a pole (the ones in alexandria that cast shadows) to determine the angle between the sun and the vertical

Question 6

how was eratosthenes able to calculate ‘angle A’ whose value was just over 7°

Answer 6

by measuring the height of his pole
and the length of its shadow at noon

Question 7

what did he assume

Answer 7

the sun was so distant that its rays of light were parallel

Question 8

assuming the rays of light were parallel, what did eratosthenes conclude

Answer 8

angles A and B were alternate angles and therefore equal to eachother

Question 9

what equation did he use

Answer 9

earth circumference / distance from syene to alexandria

360 / 7

Question 10

what did eratosthenes discover

Answer 10

circumference of the earth

Question 11

what did aristarchus discover

Answer 11

relative diameter of the moon compared with that of the earth

Question 12

how did aristarchus discover the diameter of the moon

Answer 12

observed a total lunar eclipse

Question 13

when observing the total lunar eclipse
what did aristarchus assume

Answer 13

a lunar eclipse was produced when the moon passed into the earth umbra

the sun was so far away that its rays were parallel when reaching earth

the moon’s path took it through the centre of the earth’s umbra which had the same diameter as that of earth

Question 14

what did aristarchus show

equation

Answer 14

diameter of earth
=
time interval from U1 to U2
—————
time interval from U2 to U4

Question 15

what are U1, 2, 3 and 4

Answer 15

stages of contact
thus, U1-2 = diameter of the moon and U2-4 = diameter of the earth
lowk but not exactly

Question 16

what causes tides on earth

Answer 16

mainly by the gravitational pull of the moon
and also (lesser) the sun

Question 17

what are spring tides and when do they occur

Answer 17

extra high and extra low tides
occur when the sun, moon and earth are aligned
(during new and full moon)

Question 18

what are neap tides and when do they occur

Answer 18

weaker tides (lower high and higher low)
occur when the sun and moon are perpendicular to each other
(during first and last quarters)

Question 19

why are spring tides stronger than neap tides

Answer 19

because the gravitational forces of the moon and sun combine during alignment
producing a greater tidal range

Question 20

why are neap tides weaker

Answer 20

because the sun’s gravity partially cancels out that of the moon’s
reducing the difference between high and low tides

Question 21

precession

Answer 21

slow wobble of earth’s axis
taking about 26,000 years to complete one full cycle

Question 22

how does precession affect what we see in the sky

Answer 22

changes the position of stars, constellations and where the sun and moon rise and set over long periods of time

Question 23

how does precession affect the north star

Answer 23

its position shifts
so different stars become the north star over thousands of years

Question 24

what is archeoastronomy

Answer 24

study of how ancient cultures observed and used the sky
often in religion, agriculture and architecture

Question 25

how is precession used in archaeoastronomy

Answer 25

helps researches date ancient monuments by comparing the original alignment of structures with stars or the sun to where those celestial objects would have appeared in the past

Question 26

what happens during a partial solar eclipse

Answer 26

only part of the sun is covered by the moon so the sun looks like a crescent

Question 27

what happens during a total solar eclipse

Answer 27

the entire sun is covered by the moon and the corona becomes visible

Question 28

what happens during an annular solar eclipse

Answer 28

the moon covers the centre of the sun but not the edges forming a 'ring of fire' because the moon appears slightly smaller than the sun

Question 29

what are the stages of an eclipse called

Answer 29

first / second / third / fourth umbral contact

Question 30

what causes a solar eclipse

Answer 30

moon passing between the earth and the sun blocking sunlight and casting a shadow on earth

Question 31

what causes a lunar eclipse

Answer 31

earth passes between the sun and the moon casting a shadow on the moon

Question 32

why don't eclipses happen every month

Answer 32

because the moon's orbit is tilted to earth's orbit so the sun, earth and moon don't usually line up perfectly

Question 33

when can a solar eclipse occur

Answer 33

only during a new moon when the moon is directly between the earth and the sun

Question 34

when can a lunar eclipse occur

Answer 34

only during a full moon when the earth is between the sun and the moon

Question 35

what causes a partial lunar eclipse

Answer 35

when part of the moon passes into earth's umbra creating a dark shadow on part of the moon

Question 36

what causes a total lunar eclipse

Answer 36

when the entire moon enters earth's umbra making it appear reddish

Question 37

when does a lunar eclipse happen

Answer 37

only during a full moon when the earth is between the sun and the moon