Using the virtual observatory (the link at the top of the page), examine each of the objects listed in the table. Be sure to enter the coordinates of each source exactly as they appear in the table.
  • BE SURE TO USE ONLY THE RED FILTER
  • FOR BEST RESULTS. SPECIFY "GIF" AS THE FILE FORMAT.
  • FOR THE FIELD OF VIEW USE THE VALUE LISTED IN THE TABLE.
Number
Right Ascension (RA)
Declination (Dec)
Distance (Parsecs)
Required Field of View 
    (arc minutes)
1
18 02 24
-23 02 00
1,100
15
2
22 29 36
-20 51 00
130
15
3
05 46 45
+00 04 00
500
7
4
23 58 24
+61 13 00
3,000
7
5
17 57 52
+04 40 20
2
7
6
05 34 30
+22 01 00
1,800
7
7
11 14 48
+55 01 00
4,000
7
PRINT THIS TABLE BY CLICKING "Control-P" TO MAKE DATA ENTRY EASIER!
  1. Identify items 1 through 7. Your choices are: emission nebula, star cluster, isolated star (i.e. not in a cluster), planetary nebula and supernova remnant. To remind yourself how these objects relate to stages of stellar evolution, CLICK HERE.
  2. Pick three of these objects and arrange them in the order of birth, life and death as you might expect things to go for a star like the Sun.
  3. For a really massive star the death portion of its life is different. What would you change in the above sequence to show the evolution of a high-mass star?
  4. You can easily measure the angular size of each of the objects in the table. You will be asked to find the angular size of only three objects: 1, 2, and 6. Print an image of each of these three objects. Use a ruler to get a rough estimate of the angular size of each object. Your answers will go in the boxes on question 4 of the Problems page.
  5. Convert the angular measurement into an actual size.  To do this, from the Parallax lab we use the parallax equation that the surveyor uses to measure the height of a tree:

                Actual Size = Angular Size x Distance

Remember that if both lengths are in the same units, the angular size must be in radians.

Example: Let's find the angular size and actual size of object number 7.

To find the angular size we need to know three things: the angular size of the window (which is given as the "Required Field of View" in the table), the measured size of the window, and the measured size of the object.  The angular size of the window is given as 7 arcminutes. Now measure one side of the window with the Jruler. You should get about 420 pixels.  Now measure the size of the object itself.  You should get about 200 pixels. The angular size of the object is given by the formula:

Angular Size = (angular size of window) x (measured size of object) / (measured size of window)

So, the angular size of object 7 is: 7 x 200 / 420 = 3.33 arcminutes, or (multiplying by 60) 200 arcseconds.You may have been able to estimate this by noticing that the object takes up a little less than half the window, which means it has to be a little less than 3.5 arcminutes in size.  Now remember that to convert the angular size from arcseconds to radians, divide by 206,000.  So the angular size is about 1e-3 radians.

The distance to Object 7 is given in the table as 4000 pc.  Plugging the angular size and the distance into the parallax equation, we get an actual size of 4.0 pc.

In summary, find the angular size in arcminutes, convert it to arcseconds, then to radians, and then multiply by the distance to get the actual size.

The question sheet will ask you to compare the sizes of the different objects.

If you get a message that the NASA server is too busy, keep trying. If, after 5 minutes, you still cannot get through,  CLICK HERE for an alternate way of getting the images.