ASTRONOMY 280

ASTRONOMY 280 HASTINGS LAB NOTES

PRELIMINARY DRAFT VERSION

LAB PROJECT # 1 (OBSERVATION)

Observation report format

Abstract (typically 3 sentences, goes first, written last so that you know what you should say)

I oberserved ___________ on ______________ in order to ______________. I found ______________________. I concluded ________________, in _________agreement with accepted ___________ (REFERENCE).

Sketches of observations, with directions (N, NE, etc.), date, and time (and EDT or EST). Label clearly. Indicate what you actually saw. Add verbal descriptions.

Discussion (typically 2 short paragraphs)

Conclusions

Limitations

References

For example, did you use the textbook, the lab manual, other sources, web sites, etc. ?

Reports should be clearly written. Figures can be drawn by hand in the report or on separate sheets. Reports should be complete and brief. Reports can be (1) word-processed and stapled into your notebook or (2) handwritten in to your notebook (clearly, beginning each section on a separate page).

ASTRONOMY 280 HASTINGS LAB NOTES

Experiment 1, diameter of the moon, revision 4, 20010706

Lab report format

Although this format is given in outline form, please note that lab reports are written in complete sentences.

Abstract (typically 3 sentences, goes first, written last so that you know what you should say)

1. Purpose

2. What you found (observed, measured, etc.)

3. What you concluded

Here is a sample abstract.:

The purpose of this laboratory exercise is to explore the temperature of some of the stars in Orion nebula, and also the composition of the gas clouds around the central star using digital color photography. The central stars had spectral peaks with wavelengths in the blue region or shorter, that is, wavelengths likely less than 450 nanometers, and thus temperatures of over 7000 degrees K. Other stars had spectral peaks in the green and yellow region, and thus cooler temperatures of about 5000-6000 degrees K. The gas cloud emitted red and green light, suggesting that the clouds contained hydrogen and oxygen. I concluded that digital color photography could be used to estimate some properties of nearby nebulae.

Introduction (typically 2 short paragraphs)

Purpose. You may want to begin with the first sentence in the abstract, but expanded into a paragraph.

Background. Include references where needed.

Material and methods (typically 2 short paragraphs)

What you used

Do not just list the equipment

What you did

Describe how you used the equipment

Describe how you "did the math"

Results (typically one short paragraph per result, plus sketches, graphs, calculations, etc.)

Use sketches, graphs, etc. as appropriate.

Figures can go at the end, in which case they should be labeled "Figure 1", "Figure 2", etc., and cited in this way in the text.

Calculations can go in an appendix if you wish.

Discussion (typically 2 short paragraphs)

Conclusions

Limitations

References

For example, did you use the textbook, the lab manual, other sources, web sites, etc. ?

This lab.

Purpose:

To determine the size of the moon from measurements made on earth

To determine the distance to the moon from measurements made on earth

Also, to learn about measurement and the use of proportion and scales in astronomical measurements.

Background: see text (pp 36-38).

Materials:

Photographs of lunar eclipses

Ruler

Some coins (to draw circles, and test accuracy of measurements)

Measurement technique using an arc of a circle:

The diameter of the photograph of the moon can be readily measured with a ruler, with a typical accuracy of +/- 1 mm.

The diameter of the photograph of the of the shadow of the earth can be determined as follows.

(1) Sketch the arc of the shadow.

(2) Locate where the arc of the shadow meets the boundary circle of the moon (call these points A and B).

(3) Draw the line segment AB. It is a chord to the arc of the shadow.

(4) Consider the figire below, where d is diameter of the shadow of th earth and x is the distance between the midpoint of the chord and the arc of the shadow of the earth. From Euclidean geometry we have

(d-x)x = s²,

where s is 1/2 the length of the chord AB. You can measure x and s.

(5) Solve the above equation for d:

dx - x² = s²,

dx = s² - x²,

d = s²/x - x.

Try the procedure first with the arc formed by approximately 1/6 the circumference of a quarter to learn how to do each of the above steps accurately. Your writeup should include the results of your trial matches.

Proportions and scales:

Diameter of moon (km)/Diameter of earth(km) =

Diameter of photograph of moon (cm)/Diameter of photograph of earth(cm).

You know the diameters of the photographs from your measurements. You know the diameter of the earth = approx. 12,735 km (see text, p. 135).

Diameter of moon (km)/(2 Distance to moon) (km) =

Angle subtended by moon (deg)/360(deg).

This is the small-angle formula (text, p. 40) .

Averaging to reduce error:

You should use your own data as well as data from other students (cite them) for this part of the experiment. There are use two techniques. One is to discard equal numbers of "high" and "low" results to eliminate outliers. Another is to average the results. You need to decide how to combine these techniques, and to briefly justify what you did.

Results:

Include

Photographs with measurements

Calculations of the diameter of the moon.

Averaging.

Give brief written explanations.

Discussion

Conclusions. Restate your results briefly. How do they compare with accepted values ? (Include a citation for the accepted value). If there are large differences, try to explain how they arose.

Limitations. What limited your results (in this case, the accuracy of your measurements) ? How would you overcome these limitations ?

How to cite the text

In the references:

Arny, T.T. 2000. Explorations, an introduction to astronomy, 2nd ed, 2000 update, McGraw-Hill, Boston.

In the text. Here is an example. The size of the moon was first measured using the earth’s shadow by Aristarchus (Arny, 2000, p 38).

How to cite a web site

In the references:

www.hofstra.edu/~whatever. Copyright information.

In the text (www.hofstra.edu/~whatever)

Carefully cite any photocopies or printouts you include (it is ok, and sometimes good to include them, but citation is important).

GOING FOR AN A: Ideas.

Find additional photographs from the web and analyze them.

Explain the geometry behind our method for estimating the size of the moon photograph.

Check your results by trying another method to estimate the size of the moon photograph - for example, use a cut out circle as a template, draw arcs of various circles on the photograph, etc.

Carefully explain why the small angle formula works.