EARTHWATCH 3.5 (CGA version) is a graphic program that presents in real-time a dynamic Mercator Projection map of the world including features such as: * Present daylight and night areas of the earth. * Sunrise and sunset times for a specified location and date. * Comparison of sunrise/sunset times with those of previous day. * No. of days until beginning of next season (solstices & equinoxes). * Percentage of daylight for specified date and location. * Time of day in each of the world's time zones. * Date on either side of the International Date Line. * Present sunrise and sunset zones throughout the world. * Distance of sun and moon from the earth. * Position, age, and phase of the moon. * Position of the sun on its annual trek along the analemma path. To achieve an accurate real-time rendering, the EARTHWATCH program must have six parameters properly set. They are DATE, TIME, LATITUDE, LONGITUDE, STD/DST, and TIME ZONE, and are explained on the subsequent HELP screens. DATE: This date setting is used to calculate the astronomical phenomena used by the program. Any date from the year 0 through 3000 may be entered. EARTHWATCH will keep track of the offset between the date you set and the DOS date kept by your computer's internal clock, taking into account calendar reforms and leap year reckoning. Your computer's clock will not be affected by the EARTHWATCH setting. TIME: This time setting must be the correct clock time (whether local standard or local daylight savings time) for the location chosen - most commonly your own city, designated by the LATITUDE and LONGITUDE settings. As in the case of DATE, any time may be set and EARTHWATCH will keep track of the time offset relative to the computer's clock, which will be unaffected. As a shortcut to reset the EARTHWATCH date & time to coincide with the DOS setting - just press the SPACE bar. LATITUDE: The geographical latitude (in degrees and minutes of arc) that EARTHWATCH will use to calculate sunrise/sunset times for the location chosen. North of the equator is positive, south negative. An option is presented to display a gazetteer listing over 400 cities around the world, along with their coordinates (lat/long) If your city isn't listed and you are not concerned with optimum accuracy in the EARTHWATCH display, use the coordinates of a listed city nearest you. Otherwise you can determine your co- ordinates from a map, or a more complete gazetteer such as those found in most world atlases. LONGITUDE: The geographical longitude, also in degrees and minutes, and also used by EARTHWATCH in calculating local sunrise/sunset and in positioning the map. Longitude at the Prime Meridian (through Greenwich, England) is zero. West of this meridian is positive longitude up to 180 degrees, and east is negative to -180 degrees. STD/DST: This setting depends upon whether the TIME setting refers to Standard or Daylight Savings Time. Since Daylight Savings Time regions vary with political boundries, seasons, and local legislation, EARTHWATCH makes no attempt to predict or show them on the world display. All Time Zone hours around the world are displayed across the top and and indicate the present local Standard Hour for that zone. They are updated every hour on the hour. If Daylight Savings Time applies to a particular region, the user must add one hour for the correct clock time there. TIME ZONE: Used by EARTHWATCH in conjunction with the local time to determine Greenwich Mean Time (GMT), necessary to position the map correctly. The 24 Time Zones around the world have somewhat irregular shapes and are shown by dashed lines on the map. Whenever a LATITUDE or LONGITUDE setting is changed, EARTHWATCH automatically runs a routine that graphically determines the TIME ZONE for the new setting. However, this result could be ambiguous if the new location lies near a zone border. If you wish to check the TIME ZONE value for your location, you should consult a world atlas containing a World Time Zone map. You can then manually enter your TIME ZONE number by selecting the TIME ZONE option from the CHANGE MENU. The scale used by EARTHWATCH for TIME ZONE is a value of zero for the zone occupied by Greenwich, England, and increasing as the zones proceed westward around the world up to a value of 23. Thus, for example, New York is in TIME ZONE 5, Melbourne in 14, and Rome is 23. Any of the six parameters described on the previous pages may be changed by first selecting (C) on the MAIN MENU, which invokes the CHANGE MENU. Another option (I) available from the CHANGE MENU presents the HIGHLIGHTED LOCATIONS MENU. This menu displays a set of from one to ten Latitudes & Longitudes of locations that have been pre-selected to be highlighted as white dots on the EARTHWATCH display. Along with each Lat/Long pair is space for a comment. By choosing (A), (D), or (R) from this menu, you may Add locations, Delete locations, or Return to the CHANGE MENU. Once back at the CHANGE MENU, you may select (P) to Proceed to the EARTHWATCH display, or (Q) to Quit. From the EARTHWATCH display you can always return to the MAIN MENU by pressing the ESC key. The MAIN MENU also offers the (Q) option. From the MAIN MENU, two additional options are available; (A) for ALMANAC screenand (S) for SOLUNAR data screen. The ALMANAC screen presents the following supplemental information for the date you have set for the EARTHWATCH screen: * Day number of the year. * Julian date. * Present season and number of days until beginning of next season. * Sunrise/set times with comparison to previous day's times. * Daylight interval with comparison to previous day's interval. * Solar declination and Equation of time. * Distance to the sun amd moon. * Age and Phase of the moon. The SOLUNAR screen lists Solar & Lunar data (sunrise, sunset, and phase (of the moon) for the entire month of any year from 0 through 3000. Pressing any key from either of these screens returns you to the MAIN MENU.
