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Astronomy Lab: Finding Objects in the Sky, Lab Reports of Astronomy

Syracuse UniversityAstronomy

Instructions for a lab exercise in astronomy where students learn to identify and locate objects in the night sky using a field guide and a photographic print from the national geographic society–palomar observatory sky survey. The lab covers finding the scale of the print, using sky maps, and locating specific objects in the sky using their coordinates and constellation charts.

Typology: Lab Reports

Pre 2010

Uploaded on 08/09/2009

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Name:
Partner:
Partner:
Lab 2: Finding Objects in the Sky
This lab uses a Field Guide to help you to answer questions like: Where is your Piece
of Sky (POS)? What will the sky look like tonight? Is (such and such an object) above the
horizon right now? If so, where should I look to see it? When would be the best time to
look? What is the best time of year to see it? How high in the sky does it ever appear?
1 The size of your Piece of Sky
Your Piece of Sky is represented by a photographic print from the National Geographic
Society–Palomar Observatory Sky Survey. Each photo covers a part of the sky that is about
6.5 degrees on a side.
1. Find the scale of the print
Measure the width of your print in centimeters. WIDTH = cm.
This width represents 6.5 degrees, so to find the scale in centimeters/degree, divide the
width (in cm) by 6.5 degrees.
SCALE = cm/deg.
2. Get a sense for the scale
The Moon’s angular size in our sky is 0.52 degrees, just a bit over one half degree.
To find the size the Moon would appear to be on your print, multiply your scale (in
cm/deg) by the Moon’s diameter in degrees. How big is that?
MOON DIAMETER = cm at the scale of the POS prints.
Tear out a piece of paper from your notebook of about this size, and place it on your
print. Try to remember how large the Moon looks when you see it in the sky. This is
a way of getting a sense of the scale of the print.
If you prop your Piece of Sky photo on the wall and stand back the right distance,
then you will see it at the same angular size as your real Piece of Sky occupies in the
sky. For your photo, you need to stand about 10 feet away. Stand back and admire it.
Does the piece of paper representing the Moon look about right?
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Name:

Partner:

Partner:

Lab 2: Finding Objects in the Sky

This lab uses a Field Guide to help you to answer questions like: Where is your Piece of Sky (POS)? What will the sky look like tonight? Is (such and such an object) above the horizon right now? If so, where should I look to see it? When would be the best time to look? What is the best time of year to see it? How high in the sky does it ever appear?

1 The size of your Piece of Sky

Your Piece of Sky is represented by a photographic print from the National Geographic Society–Palomar Observatory Sky Survey. Each photo covers a part of the sky that is about 6.5 degrees on a side.

  1. Find the scale of the print Measure the width of your print in centimeters. WIDTH = cm. This width represents 6.5 degrees, so to find the scale in centimeters/degree, divide the width (in cm) by 6.5 degrees. SCALE = cm/deg.
  2. Get a sense for the scale The Moon’s angular size in our sky is 0.52 degrees, just a bit over one half degree. To find the size the Moon would appear to be on your print, multiply your scale (in cm/deg) by the Moon’s diameter in degrees. How big is that? MOON DIAMETER = cm at the scale of the POS prints. Tear out a piece of paper from your notebook of about this size, and place it on your print. Try to remember how large the Moon looks when you see it in the sky. This is a way of getting a sense of the scale of the print. If you prop your Piece of Sky photo on the wall and stand back the right distance, then you will see it at the same angular size as your real Piece of Sky occupies in the sky. For your photo, you need to stand about 10 feet away. Stand back and admire it. Does the piece of paper representing the Moon look about right?

2 Practice using Sky Maps

Please read in the Field Guide the introduction to the Monthly Sky Maps, pp. 46–48. Study especially Table 6 on pp. 52–53, since that is the way to find which Monthly Sky Map is appropriate for a given date and time. Note that the table indicates that each Sky Map is visible two hours earlier each succeeding month. Carefully explain why this is true, clarifying by drawing a diagram showing the Earth, Sun, and stars.

Use the table to find which map you would use tonight at 8:00 p.m.: Open your Field Guide to the appropriate Monthly Sky Map. It is probably best to use the version that has the constellation lines marked, at least at first.

  1. Northern Constellations Study the northern sky first. Stand facing north. Hold the book in front of you with the left-hand margin down. Pick out the appropriate horizon line. Syracuse’s latitude is 43◦^ N., so the 40◦^ line is probably good enough. Next, find the marker for the location of the zenith, the point directly overhead. Now try to imagine the stars stretched out from the horizon directly in front of you to the zenith, which you can see by tipping back your head. It takes some imagination, since star maps are drawn in a very compressed way compared to the appearance of the sky. Pay the most attention to the location of the Big Dipper, an asterism that is a part of the constellation Ursa Major, and to the location of Polaris, the North Star, at the end of the handle of the Little Dipper, Ursa Minor. Draw which way will the Dippers be oriented tonight at 8:00 pm.

90 ◦^ declination (or − 90 ◦^ in the southern hemisphere) is at the center of the map. The celestial equator, with 0◦^ declination, is a circle almost at the outer edge of the map. (Each map actually extends 10◦^ into the other hemisphere.) The next step is to find where the coordinates of your POS fall in the index map. Find your R.A. around the outer edge. Now you need to move in toward the center of the map by an amount that corresponds to your dec. A good way to do this is to set a ruler along the dec scale at 12h, and find the distance in from the edge of the map to your declination. Then, set the ruler so that it is lined up with both your R.A. and with the pole at the center, and measure in the same distance. That is the center of your Piece of Sky, placed in the context of the constellations. Which labeled constellation is nearest to this position? Nearest marked constellation is. c) The General Sky Maps also serve as the index to the Field Guide’s Atlas of the Sky. The boundaries of each Atlas Chart are outlined in blue; each region is labeled with a large blue number. In which Atlas Chart does your POS fall? My POS is on Atlas Chart #.

  1. When can you see your Pieces of Sky? Determine if your Piece of Sky is visible at this time of year. Look at the Monthly Sky Map for right now to see if your constellation is above the horizon this evening at 8 p.m. If it is up, where in the sky will it be?

If it is visible tonight at 8 p.m., what time of night will be best for observing it (that is, when will it be highest in the sky)? Explain your reasoning.

Check your answer by looking at the appropriate sky map. Is your constellation high in the sky?

If it isn’t visible tonight at 8 p.m., consult other Monthly Sky Maps to determine on what date it would be best to observe it at 8 p.m.

Best date to observe my POS:.

4 Locating your Pieces of Sky in the Atlas of the Sky

  1. Turn to the Atlas Chart containing your POS. The Atlas of the Sky is found in pages 228–347 in the Field Guide. Each Chart consists of a pair of facing pages, with text

on the left and the map on the right. Flip through the book until you have found the right pages.

  1. The right ascension coordinates are marked out along the top and bottom edges of the Chart, and the declination coordinates appear on the left and right edges. Using your POS coordinates, note where on the Chart your POS is centered. Note that the constellations are marked on the Atlas Charts. The prominent stars are indicated with faint outlines of the constellation connecting them. Also, the official borders of the constellations are marked out like national boundaries, here indicated with white dashed lines. Check the location of your Piece of Sky. Is it officially in the constellation you assigned it to when you answered 2b) above? If not, to which constellation is it actually assigned? The official constellation of my POS is.
  2. As you can see from the declination scale, 6.5 degrees occupies just about 1.9 cm on these charts. Your T.A. will provide a clear plastic overlay on which is marked a square with these dimensions. Center this square on your POS coordinates. Now look at the portion of the sky within the square, and compare what you see to your POS photograph. Does the pattern of stars in the square in the Atlas match the arrangement of brighter stars in the photograph? If not, adjust the position of the square in your Atlas until it does. If this is tricky, ask your T.A. for help.

5 Detailed Observations in your Pieces of Sky

The key to the Atlas charts are fairly self-explanatory, but you may find more explanation on pp. 209–213 in the Field Guide.

  1. Scanning the Atlas Chart for interesting objects in your Piece of Sky Using the Chart and its key at the bottom, inspect your Piece of Sky and answer the following questions: a) What is the magnitude of the brightest star on your print? (note smaller magnitude means brighter) mag =. Give the names and magnitudes of any stars in your piece of sky that are bright enough to be named.

Are there any stars there that are denoted as double, multiple, or variable? If so, describe them.