The Very Best of Atari Inside

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Cadenza AstroCal (Version 1.7, September 22, 1988) Program Features This program generates (for any given year) a calendar containing the following information: 1. Times of sunrise, sunset, moonrise, and moonset for each day 2. Times and dates of Moon phases 3. Times and dates of solar and lunar eclipses 4. Times and dates of solstices and equinoxes In addition to this calendar, the program can generate: 1. A report of all lunar or solar eclipses for a range of years 2. A report of planet viewing information for a specified year 3. A report of perihelions and aphelions of planets for a range of years 4. A report of perigees and apogees of the Moon for a specified year 5. A report of the dates of Easter for a range of years The calendar and reports are all customized for the user's location. All times and dates are in local time. The calendar and reports can be printed on a printer or listed on the computer screen. Hardware Requirements This program should run on any Atari ST computer with a monochrome or color monitor. This program runs on color monitors in medium resolution only (please see the Bugs section below). Of course, users wanting to print out calendars and reports will need a printer. Menus AstroCal has the following menus: "Desk", "Describe Location", "Generate Report", "File", "Display", and "Help". The "Desk" menu can be used to run desk accessory programs, and to see the "introduction box" of this program. The "Describe Location" menu is used to specify one's location (in latitude and longitude), and the difference between local time and UT (universal time (sometimes called GMT (Greenwich Mean Time)). The "Generate Report" menu has seven submenus: "Calendar", "Lunar Eclipses", "Solar Eclipses", "Planet View Info", "Planet Distance", "Moon Distance", and "Dates of Easter". The "File" menu has only one submenu, labeled "Quit". This submenu is selected to quit the entire program. The "Display" menu has two submenus, "Scroll" and "Stop". If you select the "Stop" submenu, the program will wait for you to type the RETURN key after each page of text is listed on the display screen. If you would prefer that the program continuously write text on the display screen without stopping, select the "Scroll" submenu. The "Display" menu does not affect the printing of calendars and reports on a printer. The "Help" menu is used to get basic information about the program. Getting Started First of all you will need to provide the program with some information about your location and local time. This information is required to allow the program to customize its output for your location and time zone. Select the "Describe Location" menu with the mouse. Then select the "Describe Location" submenu. At this point you should see a "dialog box" allowing you to specify your city's name, your latitude and longitude, and the difference between your local time and UT. Type the name of your city in the space labeled "Location Name". Type in your latitude and longitude in the appropriate spaces. Note that latitude and longitude must be entered as decimal degrees. To convert an angle expressed in degrees, minutes, and seconds form to decimal degrees, use the following formula: decimal degrees = degrees + minutes / 60 + seconds / 360 For example, if you know that your latitude is 32 degrees, 12 minutes, and 44 seconds, you will need to type in a latitude of 32.21 since: 32 + 12 / 60 + 44 / 3600 = 32.21 (rounded) If you live north of the equator, select the button labeled "North". Otherwise select "South". In the same way, enter your longitude in decimal degrees, and select the "West" button if you live west of Greenwich, England, or "East" otherwise. Finally, enter the number of hours that you must add to UT to convert to your local time. If you must subtract from UT to get your local time, enter a negative number. You may enter a fractional number (e.g. 4.5). Users in the USA can use the following table: Atlantic Time Zone Local Time = UT + -4 hours Eastern Time Zone Local Time = UT + -5 hours Central Time Zone Local Time = UT + -6 hours Mountain Time Zone Local Time = UT + -7 hours Pacific Time Zone Local Time = UT + -8 hours Most of Alaska Local Time = UT + -9 hours Hawaii Time Zone Local Time = UT + -10 hours Once this information is entered, select the button labeled "Done". This information will be saved in a disk file (named astrocal.dat) and need not be entered again. Note that AstroCal gives all times and dates in local standard time, never in Daylight Savings Time or Summer Time. Now that you've specified your location, you can generate an astronomical calendar or a report. Note about entering years: if you want a calendar or report for the year 1988, enter 1988, not 88. Negative years (i.e. B.C.) can be entered. Generating an Astronomical Calendar Select the "Generate Report" menu, and then the "Calendar" submenu. At this point you should see a dialog box allowing you to specify the year of the calendar, the starting month of the calendar, and whether the calendar should be printed on your printer or on the computer screen. Once you've given this information, press the "Done" button, and the calendar will be generated. If you change your mind, press the button labeled "Cancel", and the calendar will not be generated. Preparing an astronomical calendar will take about one hour. The calendar will contain several abbreviations which are explained in the Abbreviations section later in this document. Equinoxes and Solstices in the Northern Hemisphere The celestial equator is the plane described by the Earth's equator. The ecliptic is the apparent path of the Sun across the sky during one year. Equinoxes occur when the ecliptic crosses through the celestial equator. At the March Equinox the Sun appears to cross the celestial equator on its journey north. The September Equinox happens when the Sun crosses the celestial equator going south. Solstices occur when the ecliptic is maximally north or south of the celestial equator. At the June Solstice the Sun is as far north of the celestial equator as possible. At the December Solstice the Sun is as far south as possible. Spring begins at the March Equinox, Summer at the June Solstice, Fall at the September Equinox, and Winter at the December Solstice. For the southern hemisphere, switch north and south, summer and winter, and fall and spring in the previous three paragraphs. Generating an Eclipse Report Select the "Generate Report" menu with the mouse, and then select the "Lunar Eclipses" or "Solar Eclipses" submenu. At this point you should see a dialog box prompting you for the range of years of the report, and whether the report should be printed on your printer or listed on your display screen. Press "Done" when you've entered all of the information, or press "Cancel" to quit. Interpreting a Lunar Eclipse Report During a lunar eclipse, all observers that can see the moon will see the same part (i.e. moon enters shadow, maximum eclipse, moon leaves shadow) of the eclipse at the same instant. Thus for each eclipse in the eclipse report, you will be able to view a given part of that eclipse if it occurs between the time of moonrise and moonset on the day of the eclipse. Interpreting a Solar Eclipse Report This program does not compute the local circumstances of solar eclipses. Consequently, you will not be able to determine whether a solar eclipse predicted by AstroCal will be visible in your area. Generating a Planet Viewing Information Report Select the "Generate Report" menu with the mouse, then select the "Planet View Info" submenu. At this point you will be prompted for the month and year at which the report will begin, and whether you want the report printed on your printer or on your display screen. Press "Done" when you've entered all of the information, or press "Cancel" to quit. Interpreting a Planet Viewing Information Report This report will help one determine whether or not a given planet will be visible on a given day, and its location. Planet locations are given in right ascension (expressed in decimal hours) and declination (decimal degrees). The elongation of planets is given in decimal degrees. Consider two rays originating at the center of the Earth, with one going to the center of the Sun, and the other going to the center of a planet. That planet's elongation is the angle between these rays. If a planet's elongation is near 0 (or 360) degrees, it will tend not to be visible from the Earth. To an earthbound observer planets, like the Moon, have phases. This report specifies the illuminated fraction of a planet's disk. This is a number between 0 (for a planet that is not visible (like the new Moon)) and 1 (for a planet whose disk is entirely visible (like the full Moon)). This report also gives the distance between the center of the Earth and a planet, expressed in astronomical units. One astronomical unit is equal to the average distance between the Earth's and Sun's centers (149,598,770 km). Generating a Planet Distance Report A planet achieves perihelion when it comes closest to the Sun. Aphelion occurs when a planet is at its greatest distance from the Sun. To generate a report specifying the dates of perihelion and aphelion for planets, select the "Generate Report" menu, and then select the "Planet Distance" submenu. You will be prompted for the range of years of the report, and whether the report should be printed on your printer or listed on your display screen. When you've entered this data, press "Done" to generate the report, or "Cancel" to quit. Generating a Moon Distance Report Perigee occurs when the Moon is closest to the Earth in its orbit, and apogee when it is most distant. At perigee the Moon's influence on tides is greatest. To produce a report of the dates of perigee and apogee, select the "Generate Report" menu and the "Moon Distance" submenu. Then enter the year of interest, and the starting month. Decide if the report should be listed on your display screen or printed on your printer, or select the "CANCEL" button to quit. It will take about half an hour to complete this report. In the report, the distances given are between the centers of the Earth and Moon. The diameter of the Moon is defined as follows: imagine two lines: one line extends from the Earth's center to the rightmost part of the Moon's surface. The other line goes from the center of the Earth to the leftmost part of the Moon's surface. The angle between these two lines is the diameter of the Moon. The diameter of a body is also called the body's angular size or angular diameter. Generating a Dates of Easter Report Easter is defined as (usually) the first Sunday after the fourteenth day after the first new Moon after March 21. To produce a report of the dates of Easter for a given range of years, select the "Generate Report" menu and the "Dates of Easter" submenu. Then enter a range of years, and decide if the report should be printed on your printer or listed on your computer screen. Finally, press "Done" to generate the report, or "Cancel" to quit. Quitting Early If you want to quit in the middle of preparing a calendar or report, press the Undo key. In a moment (but not immediately) you'll be given the opportunity to quit whatever you're doing and go on to something else (or quit the program entirely). Quitting the Program When you want to quit the entire program, select the "File" menu and the "Quit" submenu with the mouse button. If you've changed your location information, you will be asked if you want to save the changes. If you answer no, your changes will be discarded. If you answer yes, the changes will be saved in a disk file (named astrocal.dat) and will be available the next time you run the program. Abbreviations SR: Sun Rise SS: Sun Set MR: Moon Rise MS: Moon Set FM: Full Moon NM: New Moon FQ: First Quarter LQ: Last Quarter MEQ: March Equinox JSO: June Solstice SEQ: September Equinox DSO: December Solstice UT: Universal Time AU: Astronomical Unit RA: Right Ascension DEC: Declination DEGS: Decimal Degrees HRS: Decimal Hours ELO: Elongation ILL: Illuminated Fraction of Planet's Disk DIST: Distance from Earth Note About Accuracy The results of this program are not exact for three reasons: 1. All computer floating point arithmetic is approximate. 2. Simplifying assumptions in the astronomical calculations result in a loss of accuracy. 3. Some of the astronomical calculations are optimized for the present day, and are not as accurate for dates far into the past or future. At any rate, values computed by AstroCal for years in the last quarter of the twentieth century are usually accurate to within a few minutes, with the following exceptions: 1. Calculation of planet perihelion and aphelion: dates for the Earth may be off by more than one day, dates for Jupiter may be up to half a month in error, and dates for Saturn may be off by more than one month. 2. Calculation of Moon perigee and apogee: the time of perigee or apogee may miss the mark by an hour. Bugs and Limitations This program does not predict penumbral lunar eclipses, only umbral lunar eclipses (most of the penumbra is not dark enough to have a noticeable effect on the Moon's brightness). Umbral lunar eclipses having a very small magnitude may be missed. For example, AstroCal does not predict the lunar eclipse of March 3, 1988, which had a magnitude of only 0.003. Since this program was developed on a monochrome Atari ST, there may be some problems running the program on a color system. If you find any bugs, please report them to the author (the address is below). This program is under continuous refinement, and your bug reports and suggestions will contribute to its improvement. Further Reading Mathematical astronomy is great fun, and probably easier than you think. The two books that helped me the most in writing the program are: 1. Astronomical Formulae for Calculators by Jean Meeus (third edition), published by Willmann-Bell. Meeus' book is outstanding. Although the methods could be performed on a calculator, they are certainly viable for use in a computer program. Most of the methods used in AstroCal are drawn from this book. 2. "Practical Astronomy with your Calculator" (second edition) by Peter Duffett-Smith, published by Cambridge University Press. The methods in Duffett-Smith's book tend to be less precise than the corresponding ones in Meeus' book. However, this book is very useful as a reference. Some of the methods used in AstroCal are drawn from this book (chiefly coordinate transformations). Duffett-Smith has also written "Astronomy with your Personal Computer". This book is for someone who simply wants to type in a pre-written program to do astronomical calculations. There are many BASIC programs in this book, but less background information than in "Practical Astronomy with your Calculator". The following book contains a wealth of information about many different astronomical phenomena over a long span of years. It is extremely useful for verifying the accuracy of a program: "Astronomical Tables of the Sun, Moon, and Planets", by Jean Meeus, published by Willmann-Bell. Donald Menzel and Jay M. Pasachoff's "Stars and Planets" is a colorful and fun book. It is very useful for those who want to find and observe various stars and planets. Kim Long's "The Moon Book" (published by Johnson Books) is an interesting and fun book packed with information, diagrams, and folklore about the Moon. Most almanacs contain much astronomical data. Distribution of this Program Since Cadenza AstroCal is public domain, users may freely distribute copies of the program to other users, user groups, electronic bulletin boards, etc. Payment If you like this program, please send $5.00 US to the following address: Eric Bergman-Terrell Cadenza Software, Ltd. 1450 West 116th Avenue, #21 Westminster, CO 80234 U.S.A. For $10.00 + $2.00 postage you may order a disk containing the complete source code for this program, written in OSS Personal Pascal version 2.0. You may write to the same address to report bugs, request additional information, suggest improvements in the program, etc. If you want a reply, please include return postage (2 IRCs for those outside the U.S.A.). Enjoy the program!