Ephemeris
5-Oct-2006

Introduction

Ephemeris is a program for computing information about sunrise, sunset, moonrise and moonset for a given date and location. In addition to reporting the times of these events, it also gives compass bearings so you can predict not only when but also where on the horizon the sun or moon will rise or set. Information about the phase of the moon is also displayed. Ephemeris has a built-in database of locations you can select from a menu or you can add your own locations to the database using readily available geographical data.

Using Ephemeris

When you start the program, Ephemeris sets the date to the current date and the location to the last location used. There are two types of information Ephemeris can display -- sun/moon rise/set and moon phase data or tabulated positions of the sun and moon at 15 minute intervals. To display rise/set times, click on the Rise/Set tab near the bottom of the screen. To display sun and moon tracking information, click on the Track tab.

Changing the Date

You can change the date using the drop down menus for the day, month and year. Initially, the date is set to today's date; to reset it to today, click the Now button.

Standard, Daylight Savings, or Universal Time

You can select Standard Time (ST) or Daylight Savings Time (DT). On startup, this control on the command bar is set to DT if your computer reports that daylight savings time is currently in effect, but Daylight Savings Time is not applicable to all locations. Within the USA, Daylight Savings Time is normally in effect from the first Sunday in April to the last Sunday in October everywhere except Arizona, Hawaii and parts of Southern Indiana. Outside the USA rules vary – see the table at the end of this document for various countries.

12-Hour or 24-Hour Clock

To display times using a 12-hour clock (AM/PM), tap the command bar button labeled 12; for 24-hour (military) time format, tap the button labeled 24.

Magnetic or True North

Ephemeris displays azimuth bearings to help you predict where on the horizon sunrise, sunset, moonrise and moonset will occur. These bearings can be referenced either to magnetic north to correspond to compass readings or to true north for use with maps. For magnetic bearings, tap the command bar button labeled M; otherwise tap the button labeled T.

Selecting a Location

You can select from among the preconfigured locations using the location drop down control. For information on modifying location data or adding new locations, see below.

Sun/Moon Rise/Set Information

If the Rise/Set tab is selected, in the bottom part of its window, Ephemeris displays the times and bearings of sunrise, sunset, moonrise and moonset as well a diagram illustrating the phase of the moon labeled with % illumination (0% for a new moon and 100% for a full moon). The moon is shown reversed right to left if the current location is in the southern hemisphere. Times are in 12- or 24-hour notation depending on the 12/24 setting (see above). Bearings are in the range 0°..360° with 0° corresponding to Magnetic North or True North depending on the M/T setting (see above).

NOTE: If there is no moonrise, moonset, sunrise or sunset on a given day, the corresponding field is left blank. This situation normally occurs roughly once a month for the moon; for the sun or moon it can also happen for extended periods as you approach the north or south poles.

Sun/Moon Tracking Information

If the Track tab is selected, in the bottom part of its window, Ephemeris displays a table that lists position information for the sun and moon at 15 minute intervals during the current day. You can use the scroll bar to move the window up or down through all 96 rows of the table. Clicking the Now button in Track mode causes the entry for the current time to be scrolled to the top of the window. The tabulated data consists of the following information:

Time

Times are in 12- or 24-hour notation depending on the 12/24 setting (see above) and run from midnight to midnight in 15 minute steps.

Sun Altitude, Azimuth, and Shadow Length

Altitudes are in degrees with positive values being above the horizon and negative values below. When the altitude is negative, the sun is not visible and the corresponding values are grayed out.

Azimuths are in the range 0°..360° with 0° corresponding to Magnetic North or True North depending on the M/T setting (see above).

Shadow length is the length of the shadow cast by the sun by a vertical rod 1 unit tall. For example, if the shadow value is 1.35, this means an object 1 foot high will cast a shadow 1.35 feet long while a 20 foot flagpole would cast a shadow 27 feet long (20 x 1.35  =  27). The direction of the shadow is always 180 degrees opposite to the sun azimuth.

Moon Altitude and Azimuth

Altitudes are in degrees with positive values being above the horizon and negative values below. When the altitude is negative, the moon is not visible and the corresponding values are grayed out.

Azimuths are in the range 0°..360° with 0° corresponding to Magnetic North or True North depending on the M/T setting (see above).

Moon Phase Calendar

If the Calendar tab is selected, in the bottom part of its window, Ephemeris displays a moon phase calendar for the current month. In this mode, the Day selector and Now buttons are replaced with Prev and Next buttons you can use to switch to the previous or next month. For each day of the month, a miniature representation of the moon is displayed with the day number in its center.

Compass

If the Compass tab is selected, in the bottom part of its window, Ephemeris displays a compass rotated to place the current azimuth of the sun or moon at the top. Simply point your Pocket PC at the sun or moon (in the direction of the vertical arrow) to orient the compass to true north. The compass updates automatically once every 60 seconds. The smallest divisions of the compass face are increments of 5 degrees in azimuth; the next largest are 15 degrees. The markings at 45 degree increments are labeled with the corresponding direction names.

To switch between sun and moon mode, use the tool bar at the top of the screen. In compass mode, local magnetic declination is ignored -- compass bearings are always with respect to true north. The compass always references the current time and date regardless of other time date settings in other modes.

Color Schemes

Ephemeris supports four different color schemes which can be selected from the File menu: Black on White, White on Black, Green on Black and Red on Black. The color schemes with black backgrounds are useful after dark when you want to avoid losing your night vision.

Modifying Existing Locations or Adding New Locations

To modify an existing location, first select it from the drop down location list and then issue the File/Location command from the main menu. This displays the Location dialog box with the information for the current location filled in. Enter the new information and then tap OK.

To create a new location, issue the File/Location command from the main menu. This displays the Location dialog box. Tap the New button to create a new location, enter the information, and then tap OK.

To delete an existing location, first select it from the drop down location list and then issue the File/Location command from the main menu. This displays the Location dialog box. Tap the Delete button and then tap OK.

To modify an existing location or to create a new location, you will need to have the following information available:

Name

This is just the name you choose for the location.

Latitude and Longitude

Latitudes and longitudes are entered in decimal degrees (e.g. enter 41.50 for 41°30’). Latitudes run from -90.00° at the South pole to 90.0° at the North pole. Longitudes run from -180.00° to 180.00°. West longitudes (locations West of the Greenwich meridian) are positive while East longitudes (locations East of the Greenwich meridian) are negative.

To convert degrees, minutes and seconds to decimal degrees, you can use the following formula:

decimal degrees = degrees + minutes/60 + seconds/3600

You can obtain latitude and longitude information from an atlas or GPS device or you can look it up on the web.

For locations in the USA, see the following web sites:

http://www.census.gov/cgi-bin/gazetteer

http://mapping.usgs.gov/www/gnis/gnisform.html

http://www.geocode.com/modules.php?name=TestDrive_Eagle

http://www.bcca.org/misc/qiblih/latlong.html

For locations outside the USA, see the following web sites:

http://earth-info.nima.mil/gns/html/

http://www.bcca.org/misc/qiblih/latlong.html

Magnetic Deviation

Magnetic deviation (sometimes also referred to as Magnetic Declination) is the difference in degrees between true north and magnetic north (Negative values are West; positive values are East). By knowing the magnetic deviation at a location, Ephemeris can report azimuth angles for sunrise, sunset, moonrise and moonset as magnetic bearings so you can work directly from compass readings. Magnetic deviation varies with location on the earth and also changes very slowly with time. You can obtain magnetic deviation information for any given latitude, longitude and date from the National Geophysical Data Center web site at:

http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl

If you use this web site, the magnetic deviation is displayed as the parameter D -- before entering it into Ephemeris, remember to convert the value from degrees and minutes to decimal degrees.

Time zone

Time zones represent a time difference in hours relative to Greenwich Mean Time (GMT). While time zones are normally integers, in some locations time zones are fractional. Positive time zone values correspond to positive longitudes (West of Greenwich) and negative values correspond to negative longitudes (East of Greenwich).

For the USA and Canada, the principal time zones are:

4    Atlantic
5    Eastern
6    Central
7    Mountain
8    Pacific
9    Alaskan
10  Hawaiian

For Europe, the principal time zones are:

0    UK, Ireland, Iceland and Portugal
-1  The rest of Europe, Denmark, Sweden, Norway, Morocco, Algeria, Tunisia, and Libya
-2  Finland, Estonia, Latvia, Lithuania, Belarus, Ukraine, Romania, Bulgaria, Turkey, Greece, Israel, Jordan and Egypt

If you don’t know what time zone to enter for a given location, you can look it up on the web at one of the following web sites:

http://www.worldtimeserver.com

http://www.astro.ch/atlas

http://www.globalmetric.com/time

Daylight Savings Time Rules

The following table lists the daylight savings time rules for various countries.
For more information on daylight savings time, see:

http://webexhibits.org/daylightsaving

http://www.globalmetric.com/time

Copyright Ó 2000-2004, Jonathan Sachs
All Rights Reserved

This program may be redistributed free of charge as long as the entire program and its accompanying help file are copied intact, including this notice.

Jonathan Sachs
12 Ash Street
Cambridge, MA 02138

jsachs@dl-c.com
http://www.dl-c.com