Eclipse Path - 21 Aug 2017 Map
Created By: kirkw3
Last Updated: June 26th, 2017 1:06am
West: -171.625° East: -27.375°
Country: United States
State: Georgia, Idaho, Illinois, Iowa, Kansas, Kentucky, Missouri, Montana, Nebraska, North Carolina, Oregon, South Carolina, Tennessee, Wyoming
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This map is a transparent overlay of the path of the total solar eclipse of August 21, 2017. It shows closely calculated estimates of the centerline, north boundary, and south boundary. This overlay is intended to be displayed on Garmin devices on top of a user's ordinary map and will show the eclipse path with respect to the cities, highways, and landmarks depicted in the ordinary map.
Feel free to use this map and to pass it on to other people, but please read and pass along this disclaimer, too:
NOTICE: This eclipse path map is a close approximation but is NOT exact.
This version is an update of the previous Aug. 21, 2017 eclipse path map. As with the previous version, this map should ensure that someone reasonably inside the displayed eclipse path should witness totality. This updated map for Garmin devices was compiled based on eclipse boundary points computed at longitude intervals of 7.5 minutes by astronomy program Occult 4 by Dave Herald. Astronomical data used with this version of Occult 4 was updated in February and March of 2017. Finer resolution at various zoom levels was also specified during map compilation. The updated data and more closely spaced data points should enhance the accuracy of the map's predictions relative to the previous version. However, it cannot be exact. This map has been compared and spot checked with the NASA Interactive Google Map and with data published by NASA/GSFC's Fred Espenak and has been found to track the curves on that map closely and consistently, although not identically. (This map's curves tend to fall within approximately 100 to 500 feet of Espenak's.) Various astronomical sources incorporate slightly different eclipse elements into their calculations, which will result in slight differences in predicted eclipse path boundary lines. Also be aware that the map's curves were interpolated from a finite collection of fixed points and that rounding errors may occur during the compilation of the map. More importantly, the curves of this map do not take into account the irregular, mountainous edge of the moon. These lunar irregularities may shift the eclipse's shadow on earth by up to 1 to 3 km (0.6 to 1.9 miles) north or south. All of these factors are significant to viewers situated near the edge of the path. Those users are advised to consider the north and south limit lines as approximate when viewed at high zoom levels. Viewers should NOT use the curves of this map to position themselves at the precise edge boundaries of the eclipse path. This map's accuracy is not sufficient. Instead, those people wishing to do so should consult an accurate scientific reference just prior to the time of the eclipse, as highly accurate data cannot be calculated well in advance due to uncertainties in celestial motions.
Also included as a separate file is a GPX file of the path of the centerline only. This path file was created from the same Occult 4 data and is subject to the same accuracy limitations.
To use this map, copy the file "Eclipsepath21Aug2017.img" to the "Garmin" folder on the removable SD card in the Garmin GPS device. It should also be possible to copy the file to the device's internal memory provided the file does not share the same name as any other existing file. If you have installed a previous or different version of this map, first delete the old IMG file, as the two maps have the same map ID and cannot coexist. Exercise caution not to overwrite or delete any other files when installing this map. Then turn on the device normally and go to the start or menu screen. On many devices, go to the "Setup" menu and select the "Map" and then (or) "Map Information/Select Map" options. Two or more different maps can be displayed simultaneously on modern devices; on the list of available maps, ensure that "Eclipse Path" and a general map of the area of interest are both enabled. (This may be done on certain devices by tapping the map name and then choosing "Enable.") Return to the main menu and view the map. The eclipse path will be superimposed on the other map.
This map was created and compiled by GPSFileDepot member kirkw3 from data calculated by Dave Herald's Occult 4 occultation prediction astronomy program, version 184.108.40.206. Updates including Ephemeris DE436 and program-estimated deltaT=68.94 were incorporated into the program's computations. Data was parsed and organized with custom-written software and splitter-r580 and compiled with mkgmap-r3676 on March 18-19, 2017. While believed to be accurate within the described limitations, the author assumes no responsibility for this map file's use/misuse or any consequential damages.
This revised map was posted on GPSFileDepot.com on June 26, 2017. The previous version of this map based on Fred Espenak's published coordinate table at 2-minute time intervals is available upon request (see contact info in file). The URL links in the text above were valid on June 25, 2017.
Changes: Jun. 26, 2017 Major revision - Eclipse boundary and centerline points calculated at 7.5 minute longitude intervals by Dave Herald's Occult4 ver. 220.127.116.11 program were used as nodes which were ordered into map lines (OSM "ways" or polylines) and then complied. (Occult4 ephemeris updated to DE436 prior to eclipse boundary computation.) Higher resolution specified for map levels 1-6, first level 0 unchanged (maximum res). Eclipse boundary and centerline points at 2-minute time intervals as published by F. Espenak at https://eclipse.gsfc.nasa.gov/SEpath/SEpath2001/SE2017Aug21Tpath.html were not used for this version. IMG file depicts more of path in extreme west and east (over oceans); nearly entire path depicted. GPX path file of centerline was updated to incorporate Occult 4 coordinates used for the IMG file and no longer reflects the 2-minute time interval data from Espenak. Map description text file updated to reflect these changes and clarify descriptive text, renamed "Read_me-eclipse_path_instructions.txt. URL links were valid on June 25, 2017.
Changes: Jan. 27, 2017 Minor edits and additions to map description text file to duplicate wording on GPSFileDepot web page, referenced this web page in map description text file. Map description text file name now reads "Read_me-eclipse_path_description.txt".
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