Lecture 2

Question 1

How is Earth moving in our Solar System

Answer 1

Contrary to our perception, we are not “sitting still”
We are moving with Earth in several ways, and at surprisingly fast speeds.

Question 2

Earth rotates around its axis

Answer 2

Once every day

Question 3

Earth orbits Sun(revolves)

Answer 3

Once every year

Question 4

What direction does Earth orbit

Answer 4

It rotates in the same direction it orbits, counterclockwise as viewed from above the North Pole

Question 5

How is our Sun moving in the Milky Way Galaxy?

Answer 5

Our sun moves randomly relative to the other stars in the local solar neighbourhood
Typical relative speed of more than 70,000km/hr(20km/s)
But stars are so far away that we cannot easily notice their motion

Question 6

How do galaxies move within the Universe?

Answer 6

Galaxies are carried along with the expansion of the universe.

Question 7

How did Hubble figure out that the universe is expanding?

Answer 7

Most galaxies outside our Local Group are moving away from us
The more distant the galaxy, the faster it is receding from us
Basically: We live in a expand Universe

Question 8

How is Earth moving in our solar system?

Answer 8

It rotates on its axis once a day and orbits
the Sun at a distance of 1 AU = 150million kilometers

Question 9

How is our solar system moving in the Milky
Way Galaxy?

Answer 9

Stars in the Local Neighborhood move
randomly relative to one another and orbit
the center of the Milky Way in about 230
million years.

Question 10

How do galaxies move within the universe?

Answer 10

Most galaxies beyond the Local Group
are moving away from us with the
expansion of the universe: the more
distant they are, the faster they’re
moving.

Question 11

Are we ever sitting still?

Answer 11

No! Earth is constantly in motion, even
though we don’t notice it.

Question 12

What is Scientific Thinking

Answer 12

Scientific thinking is bases on everyday ideas of observation and trial and error experiments

Question 13

What did ancient civilizations achieve in astronomy?

Answer 13

Tracking the seasons
Daily timekeeping
Calendar
Monitoring lunar cycles
Monitoring planets and stars
Predicting eclipses

Question 14

How did Astronomical observations benefit ancient societies?

Answer 14

Keeping track of time and seasons
For practical purposes, including agriculture
For religious and ceremonial purposes

Question 15

Who could predict seasons?

Answer 15

Ancient people of central Africa (6500 BC) could predict seasons (and therefore how much precipitation they should get under normal conditions) from the orientation of the crescent Moon

Question 16

The Nebra sky disc

Answer 16

The Nebra sky disc (found near Nebra, Germany) is dated to around 1800-1600 BC. It is the oldest known depiction of astronomical phenomena and contains “golden symbols”

Question 17

Nebra Disc Golden Symbols for

Answer 17

The sun or full moon
the crescent moon
The pleiades
One angular arc (originally 2 arcs) for the angle between the sunsets at summer and winter solstices near Nebra

Question 18

Where did most of our mathematical and scientific heritage originated

Answer 18

Civilizations of the Middle East

Question 19

Why does modern science trace its roots to the Greeks

Answer 19

Greeks were the first people known to make models (or theories) of nature.
They tries to find rational explanations for patterns in nature

Question 20

How did the Greeks explain planetary motion?

Answer 20

Geocentric
Earth at the center of the universe
Heavens must be “perfect”.
Objects moving on perfect spheres

Question 21

Ptolemaic Model

Answer 21

Sophisticated geocentric model
Sufficiently accurate
Remain in use for 1,500 years

Question 22

How did Ptolemaic model explain retrograde motion?

Answer 22

planets really do go backward in this model

Question 23

Aristarchus of Samos

Answer 23

Proposed a heliocentric model of the solar system. he also made estimates for the sizes and distances of the Sun and the Moon

Question 24

How did Ptolemy explain planetary motion?

Answer 24

The ptolemaic model had each planet move on a small circle whose center moves around Earth on a larger circle

Question 25

Nicolaus Copernicus

Answer 25

Proposed a Sun-Centeres model
Use model to determine layout of solar system
The model was no more accurate than the Ptolemaic model in predicting planetary positions, because it still used perfect circles and epicycles

Question 26

Tycho Brahe

Answer 26

Compiles the most accurate (one arc minute) naked eye measurements ever made if planetary positions
Still could not detect Stellar parallax, and thus still thought Earth must be ar center of solar system (but recognized that other planets go around Sun)

Question 27

Johannes Kepler

Answer 27

Kepler first tried to match Tycho’s observations with circular orbits
But an 8 -arcminute discrepancy led him eventually to ellipses

Question 28

What is an ellipse?

Answer 28

An ellipse looks like an elongated circle

Question 29

Keplers First Law

Answer 29

The orbit of each planet around the Sun is an ellipse with the Sun at one focus

Question 30

Keplers Second Law

Answer 30

As a planet moves around orbit, it sweeps out equal areas in equal times
This means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun