This lab presents basic concepts of making figures/maps and demonstrates how these can be used to look at the distribution of galaxies in the local universe. It also provides a good opportunity to emphasize the problem that distances are difficult to determine in astronomy, so for many objects, we only know about their direction, but not their distance. Understanding the difference between 2D projections of object positions and full 3D positions is useful and will be important when doing the next lab (Mapping the Galaxy), for which only 2D projection information is used.
Students start by being given angular positions of an artificial constellation. They are asked to describe the shape of the constellation by looking at the table; this is essentially impossible. The idea is to show that graphing the positions reveals additional patterns. Start them off on the idea of graphing the positions by having them determine the minimum and maximum values of right ascension and declination so they can get appropriate limits for their plots. As they start to lay out their plots, you can explore the idea of whether the two different axes should have common scales (e.g., arcmin per inch).
As they start to make the plots, they realize that it will take forever to put all the points on the plot. This is where you can introduce the advantage of computers for this sort of work. You can show them how the computer plotting program works and the resulting graph. Probably it's better to just demo this in front of the class than bother to haul out all of the computers for students to do this themselves.
To use the plotting program, follow the link in the lab. You will first need to select the data set: choices are Constellation Home (which is what you want here), and several options from the Nearby Galaxies Catalog, which you'll use later. After selecting the data set, you will get another page where you have to select what to plot, and choose the limits. Some reasonable defaults are given to plot RA vs. DEC for the constellation, with reasonable limits. You can then hit the PLOT button to create the plot.
Next you move on to the difference between 2D and 3D positions. To show examples of 3D distributions, the students will turn themselves into a model of the Local Group in an effort to see directly how nearby galaxies are distributed. This is a good time to let the students just go at it by themselves. Make sure that they choose appropriate limits (classroom must be no larger than 2.5 Mpc across, or Local Group galaxies will all just be too close to each other to see accurately). This exercise provides insights into group dynamics; again, try to avoid getting too involved yourself, just enough to keep the students on track. Make sure everyone gets assigned to a galaxy relatively quickly and each person should try to locate themself in the classroom after the limits have been determined by consensus; don't let one or two people just go around telling everyone else where to stand. Of course, if several students have problems figuring out where they should go, they can get help from other students (or you).
After doing this, students start looking at the distribution of larger numbers of galaxies. At this point you discuss the idea of various projections of 3D distributions onto 2D planes, then have the students look at these projections for all nearby galaxies. Show them plots of the 50 nearest and the 50 brightest galaxies using the computer and discuss what the projections mean. The students then get to come up with ideas about the distribution of galaxies in the Local Universe, based on the projections in the Nearby Galaxies Catalog which are given in the lab. It is important at this point to emphasize that there is not a ``correct'' answer; we just want students to look at the plots and try to describe what they see. In fact, the Supergalactic plane is definitely discernable, but it does not jump out at you so strongly that someone is ``wrong'' if they don't see it. Note that the units on the plots of the Nearby Galaxies Catalog are in Mpc; a distance of 1 Mpc is a bit over 3 million light years.
Finally, students are reminded (or introduced) to the idea of basic morphological types of galaxies. All that needs to be introduced is ellipticals vs. spirals vs. irregulars; no need to go into any finer detail (E0-E7, Sa-Sc, tuning fork, etc.). Students in their groups can do the exercise of determining the relative frequency of different morphological types among the nearest galaxies.
Finally, students can be introduced to the morphology-density relation by showing them some 2D projections of the Nearby Galaxy atlas with points color-coded by morphological type. Use the computer plotting program to do this; again, it's probably best to just demo this in front of the class and discuss it rather than have all the students try to do it themselves with the computers. To color code different morphological types, use the "subsets" section of the plotting screen; to get subsets of the data plotted with a particular color, check the box, fill in an expression for the subset, and select the desired color. For example, by selecting Set 1, filling in ITYPE<0 (it's important that there are no spaces in your expression), and selecting Red, you will get all elliptical galaxies plotted in Red. You can then select Set 2 as well, with ITYPE>0&ITYPE<10, Green, to get spirals plotted in green, etc. etc. Absolute magnitude can also be used, maybe with different sizes of points to show the difference between brighter and fainter galaxies...