Astronomy 103L


Notes for Each Chapter

Astronomical Information

Choosing Activities

The required activity consists of Chapters 1 and 2 in the text. Chapters 3-14 each count as one additional activity. (Later chapters are designed for a more in-depth treatment of the subject; consider taking AST 367 if you are interested.) The notes in the next section contain changes to the instructions in the text.

We encourage you to develop your own personalized "track" of activities. Although the chapters are designed to be independent, you will find it useful to have completed some activities before others. We also suggest that you work on two activities at once. You can then progress on an observational activity on clear nights and on a laboratory activity on cloudy nights.

Keeping a Notebook

All your work in this class needs to written clearly in ink in your notebook. Your notebook will serve as a record of your work: your observations, calculations, and conclusions. Write down enough background information that someone else could reproduce your work.

Answering Questions

Answer all of the book's questions in your notebook. Make your answers clear enough that someone who knows nothing about the subject would understand your explanation.

Recording Data

Record your observations completely and accurately, in a table if possible. If you make a mistake, draw a single line through the observation and explain why the observation is invalid.

Drawing Graphs

Make your plots big (at least half a page) and scale them to include all your data. Label the axes and give the graph a title.

Do not connect the dots. Draw a straight line or a smooth curve through the dots if one seems to fit the data.

Writing a Summary

Write a summary in your notebook when you finish each activity. This is your chance to show us that you understand what you have done and why. The summary should address the following questions:

Turning in the Activity

Once you are done with your activity, turn in your notebook. You can hand it to an instructor or slide it into the 103L cabinet (near the floor across from RLM 13.112). We will take about a week to grade the activity. You must come to class, office hours, or make an appointment to pick up graded notebooks. If you do not pass the activity, you can redo any parts of it you had problems with. You will have the opportunity to hand in the activity twice more.


Chapter 1  Chapter 5   Chapter 9  Chapter 13
Chapter 2  Chapter 6   Chapter 10  Chapter 14
Chapter 3  Chapter 7   Chapter 11
Chapter 4  Chapter 8   Chapter 12

These notes are intended to supplement the text, not to replace it. If we do not mention a section, we think that section is self-explanatory. Do not skip anything unless we specifically state that you can omit it.

Chapter 1: Principles of Measurement (Required)

The required activity consists of chapters 1 and 2.

Section I
Assemble the cross-staff and omit the rest of this section (stop at the diagram).

Section III
Omit Question 1. You'll answer a similar question later.

Section IV
Make five measurements (not 10) at 1, 4, and 16 meter (or yard) distances. You do not have to use the wide sight like the book says. Convert each measurement to an angle with your nomograph, then calculate the range, average, standard deviation (using Snedecor's Rough Check, page 5 second column), and percent error of the angles obtained at each distance.

Make a new plot like the one you made in Section III showing the average, the average plus the standard deviation, and the average minus the standard deviation at each distance. (Don't plot the smallest and largest values, as the book asks.)

Section V
Skip Question 2. Question 3 refers to the numbers in the paragraph above it.

Section VI
Question 4 is different from Question 1; read carefully. For Question 5 "proportionally" means twice the distance gives exactly half the angle. Use the errors you calculated for your angles in Section IV to answer the question. On page 8 the text instructs you to repeat your measurement from four meters with the medium sight on your cross-staff. Skip this exercise, and don't answer Question 10.

Section VII
Measure each altitude five times (not 10).

Section VIII
Section VIII is optional.

Section IX
To calibrate your hand and fist, move forward and backward in the hall with your arm extended. Stop when your hand (or fist) just covers the 75-cm length on the wall. Your hand (or fist) now covers the same angle from your eye as the 75-cm marks. Standing at the same spot, use your cross-staff to measure the angle. The angle you measure is the calibrated size of your hand or fist. To measure your finger, mark a gap 5 cm wide and move to the distance from the wall where your finger just covers the gap. Measure your distance to the wall and use the equation on p. 7. Make each measurement once and calculate errors using the values given in the text as the "actual" sizes.

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Chapter 2: Mapping the Night Sky and its Motions (Required)

Take your observations the first clear night you can! Once we've had a couple of clear nights, we can't accept weather as an excuse for not turning this chapter in on time.

Section I
Skip Parts B, D, and E. Do each measurement three times.

Section II
Skip Parts C and D.

Section III
This section can be completed before Sections I and II (except Question 2 which still must be answered). Questions 4 and 5: Note today's date.

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Chapter 3: Lunar Surface Features

The dates of this semester's lunar phases are given at the end of this handout. Your two observations will need to be at least a week apart, so be sure to plan for this. The first quarter moon rises before sunset, while the last quarter moon doesn't come up until well after midnight.

Speak with an instructor about check-out procedures if you will need binoculars outside of class time.

Section I
Drawings with the telescope must be good enough to unambiguously identify several features.

Section II
The Sun shines from the right in all photographs; virtually all the round features are craters.

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Chapter 4: Motion and Phases of the Moon

Observations will be taken over the course of one lunar cycle (28+ days). You can obtain an SC1 chart from one of the instructors.

Section I, Part A
Take data every three-four days, not every two.

Section II
Omit the scale drawing described in the last paragraph of this section. You should be able to answer Question 6 without doing the drawing.

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Chapter 5: Motions (Orbits) in Astronomy

There are two ways to do this chapter, but the more interesting of these offers you the chance to track a planet's motion through the sky. If you would like to do this, you should start as early in the semester as possible.

Omit either Section II or Section V.

Section II
Obtain an SC1 chart from one of the instructors. Observations will take between a few days and a few weeks; you will need clear skies. Mars is the easiest planet to observe.

Section IV, Part C
In Figures 9b and 9d, the larger star symbols represent the star of smaller mass. The star with larger mass has a smaller orbit (just as the Sun has a smaller orbit than the earth).

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Chapter 6: Sun: Size and Daily Motion

Observations for this activity can be conducted during the day at home.

Section I
Be sure to use a pointed gnomon, and mark the point of the shadow on the paper.

The azimuth is the angle between due north and the Sun. Since you have recorded a shadow opposite (180 degrees from) the Sun, you need to measure the angle between the shadow and due south to obtain an azimuth.

Please turn in the sheet with your actual observations.

Section II
Omit this section.

Section III
Austin is at approximately 98 degrees W longitude.

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Chapter 7: Sun: Energy Output and Yearly Motion

Do Chapter 7 after completing Chapter 6. Again, observations can be done at home. You will need two observations two weeks apart.

Section II, Part A
Graph your measurements of altitude vs. time to determine the maximum altitude and time at local noon.

Section II, Part B:

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Chapter 8: Lenses and Mirrors

This is an in-lab activity that will take one or two periods. Use four-six lenses and one mirror.

Sections I and II
If you cannot get a sharp focus when close to the light, move the lens and screen farther away from the light. A sharp focus is necessary.

Section III
Focal length is a property of every lens. Once you have determined the focal length for a lens, you can use that focal length in any situation you place the lens in.

Section V
The image distances you found from across the room in Section III are approximately equal to the focal lengths for each lens. You can use them for the focal length in this section.

Section VI
Section VI is optional.

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Chapter 9: Cameras and Photography

You may check out a camera, cable release, and tripod; ask an instructor about check-out procedures. We provide film and a darkroom.

Section I, Part G
Questions 8 and 9 each have two answers.

Section II, Part A
Watch the rewind crank when you first wind your film. If it does not start to turn after a few winds, the film was misloaded and must be corrected.

Section II, Part B
The text is unclear on page 73. Take a series of exposures of a distant streetlight, bracketing your exposures. Choose a street light that is distant enough to appear as almost a point source; the streetlight is a model of an unknown star.

For the star trail photographs a tripod is beneficial but not necessary. You can lay the camera on the ground (for overhead shots) and lean it on a rock, pointing it approximately. The camera's field of view is wide, so you will capture some stars. Be sure to use a cable release.

Section IV
Rewind the film before you open the camera!

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Chapter 10: Using a Small Telescope

Solar observations can probably be completed over the course of a week; anything else can be done in one clear night.

Section VI
You certainly don't need to observe all the different kinds of objects to observe here. Meet with an instructor to work out a reasonable list.

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Chapter 11: Intro to Spectroscopy

This is an in-lab activity.

Section II
Omit Section II.

Section IV
AST 103L and AST 302 use spectrometers that are scaled differently. If you are using a 302 grating found in the lab, the parts of the spectrometer should be separated by 10.75" instead of 20". Make the slit as small as possible for all your observations. Record observations to the nearest 20 Å.

Section VII
Observe the sodium lamp in the lab instead of a street lamp or the Sun.

Sections VIII and IX
Omit both these sections.

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Chapter 12: Distances and Properties of Stars

This activity requires only one short observation; all other data are in the text.

Section I
All references to Figures 1 and 2 are reversed. The speed of light given in Question 2 is incorrect. The correct value is c = 300,000 km/s = 3 x 108 m/s.

Section II
From each corner of the roof draw a picture of the object whose distance you are measuring in relation to the background object. Your pictures should look like Figure 4 on page 98.

Section III
Omit Section III.

Section IV
Read Appendix 3 before beginning this section. The instructors have copies of the H-R diagram on page 107 for you to put in your notebook.

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Chapter 13: Milky Way Components: Stars, Gas, Dust

This is an in-lab activity; we have prints of the Palomar plates you need.

Section III
Measure the sizes of at least six stars; make sure that the stars you measure have a temperature given. We will provide an overlay of Figures I and II.

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Chapter 14: Studies of Galaxies

This is another in-lab activity using the Palomar plates. Ask one of the instructors for the overlay (page 129).

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Spring 1998 Lunar Phases

Tuesday, January 20Last Quarter Friday, March 13Full Moon
Wednesday, January 28New Moon Saturday, March 21Last Quarter
Tuesday, February 3First Quarter Saturday, March 28New Moon
Wednesday, February 11Full Moon Friday, April 3First Quarter
Thursday, February 19Last Quarter Saturday, April 11Full Moon
Thursday, February 26New Moon Sunday, April 19Last Quarter
Thursday, March 5First Quarter Sunday, April 26New Moon

Other Astronomical Dates

Thursday, February 26Solar Eclipse (9% of area), 12:30-2:10 p.m.
Thursday, March 12Penumbral Lunar Eclipse, 8:00 p.m.-12:30 a.m.
Friday, March 20Vernal Equinox
Sunday, April 5Daylight Saving Time begins

Bright Planets

Mercuryvisible in the east before dawn in late January, late April, early May
Venusbright morning object east all semester
Marsevening object low in the southwest through February
Jupiterbright in the southwest at sunset in late January (below Mars); morning object in southeast from late March to end of the semester
Saturnvisible in the southeast in evenings (higher than Mars and Jupiter) until mid-March

Location of Austin, Texas

Austin is at approximately 30 degrees N latitude and 98 degrees W longitude.

Painter Hall Telescope

Painter Hall houses public nights when you can observe at a 9" refracting telescope with one of the Student Observatory Directors. Public nights occur on clear Saturday nights from 8:00 to 10:00. Student nights are on clear Fridays from 9:00 to 10:00.

The telescope is easy to use, and any UT student can be checked out to observe with it. Talk to the Directors, Divas Sanwal (RLM 17.312 471-7418) or Feng Ma (RLM 13.112, 471-6486) about procedures. Lara Eakins in RLM 13.122 (471-1307) also has a handbook that explains how to go about qualifying to observe.