How to Use the Function Index

Introduction

The Astro Function Index is a listing of all the user accessible functions in the Astro Utilities. Functions are arranged into sections (Titles in Blue) by functionality. These sections are arranged by complexity: the functions in the lower sections make use of the functions in the upper section. Within sections functions are grouped under descriptive headers. Headers indicate the general type of output and input arguments for the function listings that follow. Listings contain function names and argument list (in green) and are preceded by the function return type (<brown>). The function names and arguments -- but not the return types -- are in disabled math regions for ease of copying to your worksheet (see Usage Notes). A brief description of the function and/or its arguments follows on the same line. Functions with numbered descriptions (2]) indicate equations that are usually executed together. Most of these also have a matrix equivalent. An example of the above is presented here:

Sample Section

Sample Descriptive Header for listed functions

<RETURN> Function brief description here.

Function return and argument definitions can be found by clicking the "<Arg>?" icon above each section. Details concerning the function are found in the Function Detail sheets -- explained below.

Function Detail Sheets

Clicking on section titles brings up a sheet with in-depth explanation and usage examples for the functions in that section. Function sections on these sheets are formatted as follows with additional notes below:

Function Title: describe the task to be accomplished

See Also: xxxx(): usually the function that accomplishes the opposite conversion

Note: explanatory background notes indicate function units, accuracy and usage

Resource: source of these functions

Function Section: the actual functions to accomplish the task

Example: demonstrates the function. User can change input values to test function

Resource Notes

Equations are adopted from the following listed sources. Functions may have been modified from the form found in the resources to incorporate enhanced features or return values from a different origin. The first column shows the bracketed abbreviations used in the formula sections. Underlined titles are hyperlinks for more information. If you are new to astronomical computing the [AA] reference is a very useful learning tool. See more on these resources.

[AA]: Astronomical Algorithms, Jean Meeus, Willmann-Bell, Inc., 1991 2nd Printing

[CC]: Celestial Computing, David Eagle, self-published, (issue noted in Resource)

[ESAA]: Explanatory Supplement to the Astronomical Almanac, P.K. Seidelmann, University Science Books, 1992

[PAC]: Practical Astronomy with Your Calculator, Peter Duffett-Smith, Cambridge University Press, 1979

[S&T]: Sky & Telecope, Sky Publishing Corporation, (issue noted in Resource)

[TAA]: The Astronomical Almanac for the Year 1997, US Naval Observatory, US Government Printing Office, 1996

Function Notes

The Standard edition of Mathcad does not allow programming, so nested functions were employed to reduce every task to one function call. Function placement on the sheets is predicated by the fact that each equation builds on prior equations. Here are some important points concerning functions:

· When searching for a function you may find several in a group that will work for you. For instance the first may be a general function that employs a flag to specify a type of conversion; followed by specific flagless conversions. There may be a second version of a function that takes a vector row instead of individual arguments. Several functions commonly used together may be combined in a formatting matrix to output results in a nice format. All this function packaging is done to provide flexibility to the user.

· Functions do not utilize the unit placeholder on output or argument input; check function notes for assumed units. Units are employed for conversion purposes in some formulas and cancel out in the result.

· Most functions do not attempt to round results to the stated accuracy; you should do this in your usage or make note of the accuracy in any derived functions.

· Indexed formulas have a gray background and auxiliary formulas are blue-green. Neither should be modified as this may break formulas below and on sheets that reference these formulas, as well as formulas on future sheets in this series. The auxiliary formulas are for internal use and not guaranteed to exist in future versions of this sheet -- so don't use them.

Example Notes

Example input data uses a blue background. Modify these values to test the formulas. Results are in green.