Putting Stars On The Web

What is this for?
I'm working on designing a unit in the Harvard web design web site for my Educational Technology class. This web site is one part of my unit, and it is being created for my Urban Planning class. To access the Harvard site, I need to give you permissions. I would be glad to do so, simply eMail me: salinay@umich.edu.
View Unit on the Harvard Site

When I am leading a star party, I want to make sure everyone has an accurate star chart to work from. Usually I use Abram planetarium's star charts. They are cheap and for the correct latitude, but they are also for rather early in the evening and have different star densities (go to higher or lower visual magnitude) for different months. What I have created with ArcView is a way to customize the depth (visual magnitude) as well as time of night so that I can print a star chart for a cloudy night at 4am for instance, or a clear night at midnight. I have already used this in one of my Lesson Plans.
Getting the Data

Getting my data was fairly simple. I contacted an old professor of mine who directed me to a web site where I could extract the data I needed.  Click view to see how to find the data.  I downloaded it as an excel worksheet.
Preparing ArcView for Data

In Start->All Programs->GIS Applications->ArcView GIS3.2 you will find the ArcView GIS 3.2 application. Open it. It will ask you if you want to open it with a new view. Say yes. It will ask you if you wish to create a new project with a new view. Say yes. It will ask you if you want to add data now. Say yes. Find and open s:\caen\esri\esridata\world\world30.shp.

To get a spherical projection of the world, goto View->Properties->Projections and select Projections of the World, the World from Space. Now select View->Full Extent and you will be able to see a graph of the world.

Unfortunately, the world you will see will be blue, which is difficult to see stars on. Double click on World30.shp and then on the fill box. If you just don't fill, you will get a nice white background on which to place your stars.

Importing Data into ArcView

The first step in importing your data is massaging it in Excel (ArcView likes longitude to be between -180 and 180, but the data gives it between 0 and 360), and saving it as a .dbf file. You need to be careful to format the numbers as decimal numbers or ArcView will truncate them to integers (or worse).

The second step in creating a good star map is to import the data into ArcView.  Goto the .apr window in ArcView.  Click on Tables.  Click on add.  Find your file.

Now the data is in ArcView, but ArcView won't display it yet.  Click on your view.  View->Add Event Theme.  Now choose your table, and assign x to ra and y to dec.  Ra stands for Right Ascension and is like longitude.  Dec stands for Declination and is like latitude.  Now, when you click on the box next to your file in the view window, stars appear!
Making a Map 3-D

I did take a look at making my star chart 3-D, but it seems that in order to do that, one must first create a two dimensional projection of the map. A third characteristic (in my case, distance in parsecs) is then used to raise features from the plane of the map. This loses the angular information which is important in stellar positions.

In a future exploration, I may play with this more to see if there isn't a way to project in three dimensions directly from the spherical coordinates.

Creating the Star Charts
Once I was able to create star charts in ArcView, it was a simple matter to create enough of them in Photoshop and ImageReady to make this web site. In an ideal world, I'd be able to get ArcView to make them on the fly.
Creating a Form to Calculate Which Star Chart to Use
 year  month day Latitude  hr min sec
File Number
Right Ascension
h m

After several false starts, I learned enough javascript from http://aa.usno.navy.mil/ to allow me to create a form which calculates the proper star chart to use at a given time. I am disappointed that I was not able to take latitude dependence into account.

Urban Planning: Final Project, Presentation Outline
Data Acquisition, Star Chart Creation, Calculating on a Web Site  
Home Page, About Me, ePortfolio, Lesson Plans, Papers, Old Site

Daniel D. Slosberg | salinay@umich.edu
December 10, 2003