I received my first Newton for Christmas 1997. It was a used MessagePad 120 with the 2.0 Newton OS. I enjoyed using it very much and wanted to try programming. After the obligatory "Hello World" application, I decided to try a more elaborate program. I converted Astronomical Precession, a program that I translated from a Java program that I translated from a BASIC program I found in an old issue of Astronomy magazine.
I've looked that issue recently and I can't find it. I want to credit the original author but it may be a while before I find it. I moved about 6 months ago and I still haven't unboxed everything yet!
I graduated from the University of Missouri - St. Louis (UMSL) with a B.S. in Physics, Astrophyics emphasis. UMSL has a 14" Cassegrain-Schmidt reflecting telescope that the students use for coursework. It is a compartively primitive setup because you have to set the coordinates manually in order to find a particular star (or other object) that you want to study. UMSL has a set of the SAO catalogs that lists the coordinates of thousands of stars. The problem is that all the coordinates in the catalog are for 1950! Setting the telescope to the coordinates found in the book just won't work, for two major reasons:
First, nearly everyone knows that the Earth is spinning like a top, but few people know that it is also wobbling like a top! Our axis of rotation is describing a large arc in the sky, and it takes about 26,000 years to go around. That seems like a long time but even a difference of 50 years has a measureable effect on the coordinate of a star. This wobbling motion is known as the Precession of the Equinoxes, or just Precession, for short.
Second, not only are we wobbling but the stars themselves are also moving. This is called "proper motion" and is also accounted for by this program.
So, the earth is rotating on its axis, revolving around the sun, wobbling on its axis, and the stars are all moving about, including our own Sun. It's enough to make me dizzy just thinking about it! Fortunately, the largest effects are precession and proper motion, so that's all this program takes into account. It worked well for us for several years and as far as I know, my original C++ translation is still in use.
• Usage
1) Using your favorite method, download the "Precession.pkg" onto your Newton.
2) Tap the "Precession" icon.
You will see that the program is divided into two main areas, the results and the entry area. If this is your first time running the program, you'll see that the entry area is already filled out. This star is Polaris, the North Star. I include it because the original author used it as his example, since less capable precession programs fail to "precess" it properly. If you ever want to restore this entry, just scrub out the Precession icon in the "Storage" drawer. Scrubbing out that icon will also erase any current entry you may have, so be careful!
• Parameters and their Units
R.A. is Right Ascension, and should be entered in one of the following formats:
H:M:S (or hours:minutes:seconds)
H:M (or hours:minutes)
H (or hours)
Dec. is Declination, and should be entered in one of the following formats:
D:M:S (or degrees:minutes:seconds)
D:M (or degrees:minutes)
D (or degrees)
R.A. Motion is proper motion in the Right Ascension direction in Seconds per Year (or sec/year) and is a real number. If you leave this parameter blank, it is assumed to be zero.
Dec. Motion is proper motion in the Declination Direction in Arc Seconds per Year (or arcsec/year) and is a real number. If you leave this parameter blank, it is assumed to be zero.
Initial Epoch is the date of the R.A. and Dec. that you entered above. Basically, it is the year followed by a fraction, so the middle of 1991 would be 1991.5.
Final Epoch is the date that you wish to "precess" the star to. The difference between the Initial Epoch and the Final Epoch must be less than 500 years.
• Controls
The analog clock, "i" button, and the close button server their traditional purposes.
The Now button fills in the Final Epoch with the time right NOW! This is good for when you are going observing tonight.
The Clear button simply clears all of the entry fields. It does not clear the results.
The Precess button performs the precession calculation.
• Known Problems
The window is not movable on larger screens, in particular the 2100 and (I assume) the 2000 and the EMate. I wrote it on an MP120 and only recently got a 2100. I plan to change this but it may take me a while! The program also displays more precision than is really accurate, don't depend on any digits that go further past the decimal point than your original entry.
• Disclaimer
Use this program at your own risk, I make no claims to its accuracy or suitability for any particular purpose.
