Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

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Lecture 3 ASTR 111 – Section 002

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Transcript of Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Page 1: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Lecture 3

ASTR 111 – Section 002

Page 2: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Eventually we want to be able to explain things like this

Page 3: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Observing Sessions

• 16" Dobsonian• 2 Meade 12"

SCTs• 2 telescopes

from Mason's original observatories

http://physics.gmu.edu/~hgeller/observing.htmlFall schedule to be posted …

Research I Building

http://physics.gmu.edu/~hgeller/observing.html
Page 4: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Outline

1. Suggested Reading Note

2. Quiz Discussion

3. Angular Measurements Review

4. Precision, Accuracy, and Bias Review

5. Another Parallax Problem

6. Rotation

7. The Seasons

Page 5: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Suggested Reading

• In general, the quiz and exams will be based on material that I cover in class. Almost all of this material is also covered in the book.

• Ideally you should review notes and read suggested sections in book and then take quiz.

• Suggested Reading for this quiz: Chapter 2.

Page 6: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Outline

1. Suggested Reading Note

2. Quiz Discussion

3. Angular Measurements Review

4. Precision, Accuracy, and Bias Review

5. Another Parallax Problem

6. Rotation

7. The Seasons

Page 7: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Quiz Discussion

• The quiz counts as 10% of your Lecture grade

• Your lecture and lab are independent. You will receive a separate grade for lab and for lecture on your report card

• I will post the quiz within a few hours of the end of lecture, typically on Thursday.

Page 8: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Quiz Question

degrees mins-arc 60

degree

1

mins-arc 29.87498.0

1

Apogee – farthest distance

Perigee – nearest distance

Page 9: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Where does the “hand rule” come from?

Page 10: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

)(2 R C nceCircumfere )R(S Segment

R

S

Page 11: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

)(2 R C nceCircumfere )R(S Segment

R

S D

is always in radians!

Page 12: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

R

S D

)R(S Segment

RS D

Close enough!

Page 13: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

R

S D

RS D

Close enough!

When will this approximation break down?

Page 14: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

D

Your finger

Two points on screenseparated by distance D

is angular size. D is linear size.

Page 15: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Group question

What is the ratio of the width of your index finger to the distance of your finger from your arm? Answer in degrees.

Page 16: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Outline

1. Suggested Reading Note

2. Quiz Discussion

3. Angular Measurements Review

4. Precision, Accuracy, and Bias Review

5. Another Parallax Problem

6. Rotation

7. The Seasons

Page 17: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

• Accuracy – all measurements or values are clustered around the true value (you’ll get an A for accuracy, because you are on the true value)

• Precision – all measurements are clustered but are not centered on true value

• Bias – measurements are not centered on true value

No bias

Center of red dot is true value

Page 18: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Group question

1. Can you have high accuracy and high bias?

2. Can you have low precision and high accuracy?

3. Suppose many people used the small angle formula to estimate the linear distance between two dots on the screen. They all sat in the same seat while making the measurements. Will there be a bias in their measurements?

Page 19: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Outline

1. Suggested Reading Note

2. Quiz Discussion

3. Angular Measurements Review

4. Precision, Accuracy, and Bias Review

5. Another Parallax Problem

6. Rotation

7. The Seasons

Page 20: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Group question

1. How many light-years are in 10 parsecs?

2. How many light-years could a human travel in a space craft?

3. Which is larger, a parsec or an AU?

4. Why do you think we have two units, the parsec and the light year, when they are so close to each other? (1 parsec = 3.26 light-years)

Page 21: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

To describe the distances to stars, astronomers use a unit of length called the parsec. One parsec is defined as the distance to a star that has a parallax angle of exactly 1 arcsecond.

Earth(January)

Earth(July)

Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35

Distant Stars

PA

Page 22: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

To describe the distances to stars, astronomers use a unit of length called the parsec.

One parsec is defined as the distance to a star that has a parallax angle of exactly 1 arcsecond.

Earth(January)

Earth(July)

Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35

Distant Stars

PA

1 pa

rsec

Page 23: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Group Question

• If the parallax angle for Star A (PA) is 1 arcsecond, what is the distance from the Sun to Star A? (Hint use parsec as your unit of distance.) Label this distance on the diagram.

• Is a parsec a unit of length or a unit of angle?

• As Star A moves outward, what happens to its parallax angle?

Page 24: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Outline

1. Suggested Reading Note

2. Quiz Discussion

3. Angular Measurements Review

4. Precision, Accuracy, and Bias Review

5. Another Parallax Problem

6. Rotation

7. The Seasons

Page 25: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Thinking about rotation

With parallax, we learned that the position of a near object relative to a distant object can change if the observer moves.

With rotation, the time it takes for the position of a near object to change relative to a distant object can be different if the observer moves.

Page 26: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Slippage Meaning

• When you skid a tire, there is slippage – same part of tire always touches ground

• When you roll a tire, there is no slippage – different parts of tire touch ground

Page 27: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

B

George B looking straight to the left(at a distant object)

Table

Page 28: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

B

I can get him across the table by “skidding” or “slipping” – the 9 always touches the table. In this case he always is looking to the left at the distant object.

Table

Page 29: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

B

Instead of “skidding” or “slipping”, he can “roll”. On a flat table, he will look at same place in distance after 1 revolution – or after he has “rolled” the distance of his circumference

Table

Page 30: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Group Question• Rotate B around A with

slippage. How many times does George B look straight to the left?

– With slippage, the 9 on the top quarter always touches the bottom quarter

• Rotate B around A without slippage (like a gear). How many times does George B look straight to the left?

– Without slippage, first the 9 in the 1993 on the top quarter touches the bottom quarter, then 1 then the “In God We Trust”.

A

B

(A is glued to the table)

Page 31: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 32: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 33: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Question• Rotate B around A without

slippage (like a gear). How many times does B rotate?

1. Same as when B was a quarter

2. More than when B was a quarter

3. Less than when B was a quarter

(A is glued to the table)

A

B

Page 34: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Question• Rotate B around A without

slippage (like a gear). How many times does B rotate?

1. Same as when B was a quarter

2. More than when B was a quarter

3. Less than when B was a quarter

(A is glued to the table)

A

B

Page 35: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Sidereal Time Definition

• From text: “A sidereal day is the time between two successive upper meridian passages of the vernal equinox. By contrast, an apparent solar day is the time between two successive upper meridian crossings of the Sun.”

Page 36: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Or

Sidereal Time = star timeSidereal Day = the length of time it

takes for a star to repeat its position in the sky.

Solar Time = sun timeSolar Day = the length of time it takes

the sun to repeat its position in the sky.

Page 37: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Someone in back of room (distant object)

StageStudent

Instructor

Top view of classroom

Page 38: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Line 1 goes through sun and distant star

Sidereal Time = star time

Solar Time = sun time At 1,

line points at sun and distant star

Page 39: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Line 1 goes through sun and distant star

• Sidereal Time = star time

• Solar Time = sun time

Line 1 goes through sun and distant star

At 2, 24 sidereal hours since 1, line is now pointing at distant star only

At 1, line points at sun and distant star

Page 40: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

At 3, 24

solar

hours

since 1,

line

points at

sun only

• Sidereal Time = star time

• Solar Time = sun time

• Which is longer?

1. Sidereal day

2. Solar day

At 2, 24 sidereal hours since 1, line is now pointing at distant star only

At 1, line points at sun and distant star

Page 41: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Key

• A solar day is longer than a sidereal day

• This means it takes longer for the sun to repeat its position in the sky than a distant star

Page 42: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

1. West

2. East

3. Vertical

Where is Cygnus 24 sidereal hours later?

Page 43: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Where is Cygnus 24 solar hours later?

1. West

2. East

3. Vertical

1. West

2. East

3. Vertical

Page 44: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Outline

1. Suggested Reading Note

2. Quiz Discussion

3. Angular Measurements Review

4. Precision, Accuracy, and Bias Review

5. Another Parallax Problem

6. Rotation

7. The Seasons

Page 45: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Seasonal Stars• Where do the names of

the zodiac come from? During certain months, a constellation is (approximately) behind the sun

• Approximately, because precession has caused things to shift a bit.

http://historyday.crf-usa.org/1708/images/zodiac.jpg

Page 46: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

What causes the seasons?

1. Distance of the sun from earth2. Tilt of Earth with respect to the

ecliptic3. Both4. None of the above5. Primarily 2., but with a small

contribution from 1.

Page 47: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Group question

At summer solstice, when the sun is highest in the sky, who is closer to the sun

• A person on Tropic of Capricorn

• A person on Tropic of Cancer?

Page 48: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 49: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

Sun-Earth Distance

• December: 147 million km

• June: 152 million km

• September: 150 million km

• March: 149 million km

Page 50: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 51: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 52: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

The ecliptic is the imaginary plane that the Earth moves on as it rotates around the sun

Page 53: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 54: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 55: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

The Celestial Sphere

• Sometimes it is useful to think of the stars and planets as moving along a sphere centered on Earth

Page 56: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 57: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 58: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 59: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.
Page 60: Lecture 3 ASTR 111 – Section 002. Eventually we want to be able to explain things like this.

The two circled yellow arrows point to the same line of latitude.The right arrow is perpendicular to surface.The left arrow is less than perpendicular to surface.


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