SHADOW - a utility to help map Asteroid and Lunar Graze Paths

Asteroids orbiting within our solar system occasionaly move in front of stars casting a shadow on the earth. If this event is accurately timed, it can reveal much about the size and orbit of the asteroid. This is one aspect of astronomy where a "mobile" person can contribute worthwhile science, with often modest equipment.

This webpage offers a freeware utility that allows quick and easy mapping of the predicted path of an asteroid shadow (or lunar graze).
[Asteroid Shadow on Christchurch]
Shadow path of asteroid "Brita on Jul 12 2005" passing over Christchurch (New Zealand) - home of Kiwi Geoff. The above map was ccreated in a few seconds by downloading data from Steve Preston's great Asteroid Occultation Update service. "SHADOW.EXE" read Steve's "Detailed info" text file, and created a number of files for various mapping programs. You can see how the path crosses New Zealand and heads over the horizon towards Tasmania.
[Christchurch again]
Another view of Christchurch, showing how you can get many viewpoints using the wonderful new freeware Google Earth software.
We can see the middle of Christchurch is halfway between the center of the path (GREEN) and the edge of the Asteroid shadow (BLUE).
[South Island of N.Z.]
A more conventional view of the South Island of N.Z. showing the asteroid path.
SHADOW allows "blink of an eye" creation of waypoints and tracks for mapping programs or GPS. By prior connection to the Internet, the latest predictions from Steve (that use the most recent astrometry) can be obtained. The color code in the above maps is: GREEN = path center, BLUE = Asteroid shadow limits, RED = 1 sigma error lines.

SHADOW creates the following file formats:

Waypoint Files created:  (dots on map)

   POINTS.GPX  (for EasyGPS etc)
   POINTS.WPT  (for OziExplorer)
   POINTS.DBF  (for Precision Mapping Streets, dBASE, Excel, etc)

Track Files created:  (lines on map)

    TRACK.GPX  (for EasyGPS etc)
    TRACK.GEN  (precursor file for making ESRI shapefiles)
    TRACK.PLT  (overlay for OziExplorer)
    TRACK.CMX  (overlay for Precision Mapping Streets)
       SA.TXT  (overlay for Delorme Street Atlas)
    TRACK.MIF  (overlay for MS MAPPOINT)
    TRACK.GOO  (overlay for Google Maps API)
    TRACK.KML  (overlay for Google EARTH)
WPT and PLT are native formats for OziExplorer , a popular Moving Map program. The files can also be read by the freeware GPS Trackmaker.

The DBF and CMX files can be read by Precision Mapping Streets - a street-level mapping program of the United States. The DBF (dBASE format) file can also be read by Excel, dBASE etc.

An overlay file (SA.TXT) is created for the Delorme Street Atlas mapping software suite.

An overlay file TRACK.MIF is created for the MapPoint Spatial Data Import COM Add-in for MS Mappoint.

The file TRACK.GOO is used for Google Maps API - to allow Interactive Maps on web pages.

The file TRACK.KML is the overlay for the wonderful Google Earth freeware, as exampled on this page.

Rather than using Moving Map software, if you have a Garmin, Magellan or Lowrance GPS receiver, you can use the freeware program EasyGPS to transfer the GPX file (created by SHADOW) to the GPS receiver without manual entry. EasyGPS also allows you to edit the waypoints. For example you can quickly create a subset of co-ordinates that are within a defined radius of your location - so that fewer waypoints are loaded into the GPS.

EasyGPS also connects you to mapping and information sites on the Internet, giving you one-click access (from a waypoint) to street and topo maps, aerial photos, weather forecasts, and nearby attractions.

If GPX is not your preferred format, you can use GPSBABEL to convert the GPX file to many other common formats for your mapping OR GPS device.

If you have Microsoft Streets and Trips or AutoRoute. Tony George has written a set of instructions to convert the GPX (from SHADOW) to a file that can be used by Streets and Trips.


After you have downloaded SHADOW.ZIP (right mouse click, save Target As) file. Unzip it to a new directory, perhaps called SHADOW.

For Asteroidal Path files:

1. Use the Internet to access Steve Preston's Asteroid Occultation Update service.

2. Choose an asteroid event that is near your location.

3. This brings up a new webpage, that contains a link to "Detailed Info". Right Mouse click on "Detailed Info" and 'Save Target As' PATH.TXT into the directory on your PC you have used for SHADOW.EXE

4. Run SHADOW.EXE - will automatically detect the lunar or asteroidal file format and generate data in a form that can be used with your moving map software, or loaded into your GPS.

For Lunar Graze Path files:

Use WinOccult to generate a lunar graze, the output text format must be in "DD MM SS" format and the name must be "PATH.TXT" for SHADOW to auto detect and convert the file. You can also use the output of "GrazeReg" (2006 version) to make maps. Copy and paste all the contents from Grazereg to Notepad, and save as 'PATH.TXT'.

[Baja Graze]
Google Earth (using KML created by SHADOW) example graze (green line) over Baja Peninsula (on 22 March 2006)

[Garmin Etrex Vista C screen dump]

Screen dump from my Garmin Vista C, after uploading TRACK.GPX to GPS (Graze line in green).

[Garmin Etrex Vista C screen dump]

Zooming in (with Vista) near San Jose Del Cabo, where the airport is 10,808 km NEE (65 degrees) of my location in NZ (Graze line in green).

[Garmin Etrex Vista C screen dump]

This screens shows how the GPS can be used to measure from any point on the map. We can see the (green) graze line is 8.6Km south west (214 degrees) from the airport. Of course the normal use would be to show ones own position (real-time), relative to the graze line.


SHADOW was compiled as a 16bit DOS application, which will also run in Windows. It does not affect the registry or any system files, it only reads "path.txt" and creates the above files, in the directory you run the program from.

I have added (March 2007) various files to the ZIP file to allow a person to make their own Interactive Google Maps, for their website. Details can be found in the ZIP archive on how to do this.

I used Google Earth to create the above maps (except for Garmin screens).
Many thanks to the following:

Dave Gault (Blue Mountains, Australia) who happened to mention to me in passing that he was trying to get Steve's predictions into his Moving Map OziExplorer software - thus I came to write SHADOW.

Walt Morgan (California, USA) for his testing of files with Precision Mapping Streets.

Oliver Kloes (Eppstein-Bremthal, Germany) for advising that SHADOW can work with the freeware GPS Trackmaker.

Derek Breit, for help with Google Interactive Map research and testing. Breit Ideas Observatory..

Steve Preston for providing an excellent prediction service.
SHADOW written by Kiwi Geoff
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