Homework #1Homework #1Due TODAY, August 31, 6PM

Designed to get your familiar with the MasteringAstronomy.com interface

Remember, you lose 0.4% per hour you are late.

Due TODAY, August 31, 6PM

Designed to get your familiar with the MasteringAstronomy.com interface

Remember, you lose 0.4% per hour you are late.

Homework #2Homework #2 Due Wednesday, September 9, 6PM

Covers Chapters 1, 2, and 3

Estimated time to complete: 1 hour 10 minutes (so don’t wait until the last minute!) – can stop and start as you wish

Read chapters, review notes before starting

Some questions have multiple parts – do not skip them

For some of the drag-and-drop ordering questions, two or more of the answers might be in the same location (i.e., two objects might have the exact same age if you are sorting by age). In this case, place the two answers on top of each other.

Note: Incorrect guesses will count against you.

Due Wednesday, September 9, 6PM

Covers Chapters 1, 2, and 3

Estimated time to complete: 1 hour 10 minutes (so don’t wait until the last minute!) – can stop and start as you wish

Read chapters, review notes before starting

Some questions have multiple parts – do not skip them

For some of the drag-and-drop ordering questions, two or more of the answers might be in the same location (i.e., two objects might have the exact same age if you are sorting by age). In this case, place the two answers on top of each other.

Note: Incorrect guesses will count against you.

When can solar eclipses occur?

When can solar eclipses occur?

Solar eclipses can occur only at new moon.Solar eclipses can be partial, total, or annular.Total eclipses last no more than 7½ minutes at any location on Earth!

Solar eclipses can occur only at new moon.Solar eclipses can be partial, total, or annular.Total eclipses last no more than 7½ minutes at any location on Earth!

When can solar eclipses occur?

When can solar eclipses occur?

Solar eclipses can occur only at new moon.Solar eclipses can be partial, total, or annular.Total eclipses last no more than 7½ minutes at any location on Earth!

Solar eclipses can occur only at new moon.Solar eclipses can be partial, total, or annular.Total eclipses last no more than 7½ minutes at any location on Earth!

Annular eclipse occurs when Moon is far and/or Sun is near Earth.

Why don’t we have an eclipse at every new and full moon?

The Moon’s orbit is tilted 5° to the ecliptic plane.So we have about two eclipse seasons each year, with

a lunar eclipse at full moon and solar eclipse at new moon. Most months, no eclipses happen.

Why don’t we have an eclipse at every new and full moon?

The Moon’s orbit is tilted 5° to the ecliptic plane.So we have about two eclipse seasons each year, with

a lunar eclipse at full moon and solar eclipse at new moon. Most months, no eclipses happen.

Summary: Two conditions must be met to have an eclipse:

Summary: Two conditions must be met to have an eclipse:

1. It must be full moon (for a lunar eclipse) or new moon (for a solar eclipse).

AND2. The Moon must be at or near one of the two points in its orbit where it

crosses the ecliptic plane (its nodes) – in other words, the line-up in geometry of the Sun-Moon-Earth system must be nearly perfect.

1. It must be full moon (for a lunar eclipse) or new moon (for a solar eclipse).

AND2. The Moon must be at or near one of the two points in its orbit where it

crosses the ecliptic plane (its nodes) – in other words, the line-up in geometry of the Sun-Moon-Earth system must be nearly perfect.

This explains why eclipses are rare.

In the distant past, the Moon was significantly closer to Earth than it is now. At that time, total solar eclipses were:

In the distant past, the Moon was significantly closer to Earth than it is now. At that time, total solar eclipses were:

A) more common than nowB) less common than nowC) same frequency as nowD) did not occur at all

In the distant past, the Moon was significantly closer to Earth than it is now. At that time, total solar eclipses were:

In the distant past, the Moon was significantly closer to Earth than it is now. At that time, total solar eclipses were:

A) more common than nowB) less common than nowC) same frequency as nowD) did not occur at all

If Moon was closer, its angular size was larger, and more easily totally blocked the light of the Sun nearly-perfect alignment of Sun-Moon-Earth not as necessary.

Path of August 21, 2017 Eclipse

Other Future EclipsesOther Future Eclipses

2017 and 2024 eclipses can both be seen in Carbondale, IL, Cape Girardeau, MO, and Paducah, KY

Planets Known in Ancient Times

Planets Known in Ancient Times

• Mercury – difficult to see; always

close to Sun in sky• Venus

– very bright when visible; morning or evening “star”

• Mars – noticeably red

• Jupiter – very bright

• Saturn – moderately bright

• Mercury – difficult to see; always

close to Sun in sky• Venus

– very bright when visible; morning or evening “star”

• Mars – noticeably red

• Jupiter – very bright

• Saturn – moderately bright

Planet means “wanderer” in Greek.

What was once so mysterious about planetary motion in our

sky?

What was once so mysterious about planetary motion in our

sky?Planets usually move slightly eastward from night to night relative to the stars (since the planets are moving around the Sun).

But sometimes they go westward relative to the stars for a few weeks: apparent retrograde motion.

Planets usually move slightly eastward from night to night relative to the stars (since the planets are moving around the Sun).

But sometimes they go westward relative to the stars for a few weeks: apparent retrograde motion.

Uranus

Mars at 5-8 day intervals

Apparent retrograde motion — try it yourself!

Apparent retrograde motion — try it yourself!

We see apparent retrograde motion when we pass by a

planet in its orbit.

We see apparent retrograde motion when we pass by a

planet in its orbit.

Explaining Apparent Retrograde Motion

Explaining Apparent Retrograde Motion

Easy for us to explain: occurs when we “lap” another planet (or when Mercury or Venus laps us).

But very difficult to explain if you think that Earth is the center of the universe!

In fact, ancients (Greeks) considered but rejected the correct (Sun-centered) explanation for our Solar System.

Easy for us to explain: occurs when we “lap” another planet (or when Mercury or Venus laps us).

But very difficult to explain if you think that Earth is the center of the universe!

In fact, ancients (Greeks) considered but rejected the correct (Sun-centered) explanation for our Solar System.

Why did the ancient Greeks reject the real explanation for planetary

motion?

Why did the ancient Greeks reject the real explanation for planetary

motion?• Their inability to observe stellar parallax was a major factor.

Highly exaggerated, but you get the point

With the naked eye, stars would have to be at a distance of ~0.05 light years or closer for parallax to be detectable (almost 100 times closer than the closest star)

Parallax: apparent shifting of position of a foreground object relative to background objects (think: finger in front of clock)

The Greeks knew that the lack of observable parallax could mean one

of two things:

The Greeks knew that the lack of observable parallax could mean one

of two things:

1. Stars are so far away that stellar parallax is too small to notice with the naked eye.

OR2. Earth does not orbit the Sun; it is the center of the

universe.

With rare exceptions such as Aristarchus, the Greeks rejected the correct explanation (1.) because they did not think the stars could be that far away.

Thus, the stage was set for the long, historical showdown between Earth-centered and Sun-centered systems.

1. Stars are so far away that stellar parallax is too small to notice with the naked eye.

OR2. Earth does not orbit the Sun; it is the center of the

universe.

With rare exceptions such as Aristarchus, the Greeks rejected the correct explanation (1.) because they did not think the stars could be that far away.

Thus, the stage was set for the long, historical showdown between Earth-centered and Sun-centered systems.

Chapter 2 Study GuideChapter 2 Study Guide1) 88 constellations have no real physical significance (just

used to divide up the sky)

2) The celestial sphere is the projection of the Earth’s surface onto the sky – poles and equator

3) Ecliptic – the path the Sun takes eastward through the sky relative to the background stars (@1 degree per day) – caused by Earth’s motion around Sun

4) Altitude of Polaris gives your latitude on Earth

5) Earth’s 23.5 degree tilt causes seasons and different lengths of daylight throughout the year

1) 88 constellations have no real physical significance (just used to divide up the sky)

2) The celestial sphere is the projection of the Earth’s surface onto the sky – poles and equator

3) Ecliptic – the path the Sun takes eastward through the sky relative to the background stars (@1 degree per day) – caused by Earth’s motion around Sun

4) Altitude of Polaris gives your latitude on Earth

5) Earth’s 23.5 degree tilt causes seasons and different lengths of daylight throughout the year

Chapter 2 Study GuideChapter 2 Study Guide

6) Know meaning of solstice, equinox and when they occur

7) Earth’s spin precesses (wobbles) over 26,000 year period Polaris will not be the Pole Star in a few thousand years

8) Know lunar phases, and understand geometry of Sun-Earth-Moon system (picture in your mind, don’t memorize) – Earth shadow does not cause Moon phases!

9) The Moon DOES rotate (once every 29.5 days) so that we never see the back side of the Moon

6) Know meaning of solstice, equinox and when they occur

7) Earth’s spin precesses (wobbles) over 26,000 year period Polaris will not be the Pole Star in a few thousand years

8) Know lunar phases, and understand geometry of Sun-Earth-Moon system (picture in your mind, don’t memorize) – Earth shadow does not cause Moon phases!

9) The Moon DOES rotate (once every 29.5 days) so that we never see the back side of the Moon

Chapter 2 Study GuideChapter 2 Study Guide10) Know geometry of solar, lunar eclipses, and why they do not

happen at every new/full Moon

11) Go see the August 2017 total solar eclipse!

12) Planets undergo retrograde motion, where they move backwards (westward) in their path among the stars natural consequence of Earth lapping them/being lapped

13) Retrograde motion easy to explain in Sun-centered systems, difficult in Earth-centered systems

14) Greeks considered this, but rejected Sun-centered solar system because they could not measure the parallax of any of the stars thought stars could not be that distant

10) Know geometry of solar, lunar eclipses, and why they do not happen at every new/full Moon

11) Go see the August 2017 total solar eclipse!

12) Planets undergo retrograde motion, where they move backwards (westward) in their path among the stars natural consequence of Earth lapping them/being lapped

13) Retrograde motion easy to explain in Sun-centered systems, difficult in Earth-centered systems

14) Greeks considered this, but rejected Sun-centered solar system because they could not measure the parallax of any of the stars thought stars could not be that distant

Chapter 3The Science (and History) of

Astronomy

Chapter 3The Science (and History) of

Astronomy

How did astronomical observations benefit ancient

societies?

How did astronomical observations benefit ancient

societies? Keeping track of time and seasons• for practical purposes, including agriculture• for religious and ceremonial

purposes• aid to navigation

However, few cultures used the scientific method to learn about the nature of the Universe (Greeks were an exception), thus they were not truly studying astronomy.

Ancient people of central Africa (6500 BC) could predict seasons from the orientation of the crescent Moon.

England: Stonehenge (completed around 1550 B.C.)

England: Stonehenge (1550 B.C.)

Southwest United States: “Sun Dagger” marks summer solstice

Scotland: 4,000-year-old stone circle; Moon rises as shown here every 18.6 years.

Macchu Pichu, Peru: Structures aligned with solstices.

South Pacific: Polynesians were very skilled in art of celestial navigation.

France: Cave paintings from 18,000 B.C. may suggest knowledge of lunar phases (29 dots)

"On the Xinwei day the new star dwindled."

"On the Jisi day, the 7th day of the month, a big new star appeared in the company of the Ho star."

China: Earliest known records of supernova explosions (1400 B.C.) China: Earliest known records of supernova explosions (1400 B.C.)

Bone or tortoiseshell inscription from the 14th century B.C.

Days of week were named for the Sun, Moon, and visible planets.

• Greeks were the first people known to make models of nature.

• They tried to explain patterns in nature without resorting to myth or the supernatural.

Greek geocentric model (c. 400 B.C.)

Why does modern science trace its roots to the Greeks?

Eratosthenes Measures Earth (c. 240 B.C.)

Calculate circumference of Earth:7/360 = (Alexandria-Syene distance)/(circum. Earth) circum. Earth = 5000 360/7 stadia ≈ 250,000 stadia

Measurements:Syene (modern day Aswan) to Alexandria distance ≈ 5000 stadia angle = 7°

Compare to modern value (≈ 40,100 km): Greek stadium ≈ 1/6 km 250,000 stadia ≈ 42,000 km

First day of summer at noon: Sun shone directly into a well in Syene, but missed the well in Alexandria by 7°.

Greeks were quite well aware that the Earth was round.