According to almost all opinions, the Halachic Date Line is not determined by what the locals call “Saturday” and therefore, the fact that Samoa changes the date line does not change when we keep Shabbos.
As far as I know, until this point, there has not been a very exact map allowing one to determine with clarity the exact parts of the world affected by the Halachic Date Line. As an example see Rabbi Yisroel Taplin’s sefer Taarich Yisrael תאריך ישראל for a discussion about possibly not visiting the Philippines due to questions about the exact location of the date line. With the introduction of the Halachic Date Line Map such ambiguities can be laid to rest since users can zoom in to find the exact locations of various opinions on the map (see the map partially zoomed in to the Philippines for example).
Location of the Halachic Date Line
There are various opinions about the location of the halachic date line. The three main opinions of the location of the Halachic Date Line are:
Rabbi Yechiel Michel Tucazinsky (author of the Gesher Hachaim) who wrote the היומם בכדור הארץ Hayomam Bekadur Haaretz stating his opinion that the date line is 180° east (or west) of Har Habayis. Among those agreeing with this opinion is Rabbi Elyashiv. Since this line is exactly halfway around the world from Yerushalayim, a person on different sides of this line will face different directions when davening (using the rhumb line method). A person located west of the line will daven westward, and a person east of the line will daven eastwards. See the Bearing to Yerushalayim Map for a location along this line (the green line). Click on the blue pushpin in the map (below the green line) for additional information on the antipodal point of the Har Habayis.
The locations of the three lines are mostly over the Pacific Ocean, but in some places the lines intersect dry land. Examples of this are Russia, Korea and Australia that are split by the Kuzary and Baal Hamaor’s line (see the map above). The Chazon Ish brings the opinion of the Yesod Olam (a disciple of the Rosh) that when the line intersects dry land, the line is extended eastward (or on occasion westward according to the 180° opinion). This extension is referred to as “Graira”, where the land to the west “drags” the land it is attached to, to within the line. In the map, both the 90° (Chazon Ish) and 180° (Rabbi Tucazinsky) lines are measured from Har Habayis. Specifically the measurements in the map are from the center of the Dome of the Rock. This is the location of the Kodesh Kodashim according to the Radvaz. According to the Radak the center of the Dome of the Rock is the location of the Mizbeach, and the Kodesh Kodashim is 101 amos (about 54 meters / 180 feet) west of this point. According to the Radak the International Date Line would be 101 amos west of the lines in the map.
How the Map Works
The Halachic Date Line Map works like any other Google Map. You can zoom into any area to see a close-up. Clicking on the lines and shaded in “Graira” areas will provide some details about it. The map will show a very clear and exact position of the Halachic Date Line according to different halachic opinions.
Interesting points on the map
Tahania Atoll, a small atoll in French Polynesia that is intersected by Rabbi Tucazinsky’s line. To the south of this point is the island of Rapa Iti. There is an interesting Halachic phenomenon at this location with Kiddush Levana in December 2027. See Rabbi Heber’s Sefer Shaarei Zemanim שערי זמנים. Rabbi Heber graciously allowed me to post סימן ד׳ – קונטרס זמן קידוש לבנה of the Shaarei Zemanim here. The discussion of Kiddush Levana on Rapa Iti appears on page 14 of the pdf which is page 32 in the sefer.
Ikema Island is intersected by the Baal Hamaor’s line. According to the Chazon Ish “Graira” covers the entire Ikema Island, but would not (according to Rabbi Dovid Heber of the Star-K) extend over the bridge to Miyakojima Island.
The line of the Baal Hamaor runs through Changchun, China a city of 7 million. According to the Chazon Ish, “Graira” would mean the line does not split the city.
Are islands on Lake Argyle, a 100 miles inland but with a river leading to the ocean included in Graira using the Chazon Ish’s line? According to Rabbi Heber the river would “not ruin graira”, and such islands would be included. Would you say the same thing for French and Phillip Islands near Melbourne, Australia? Rabbi Heber is of the opinion that one should be machmir on these islands.
Clarity about exactly what parts of the Philippines are on the other side of the date line. Some say it is better not to travel to the Philippines due to questions of the placement of the Baal Hamaor/Chazon Ish line, but the date line map clarifies any ambiguities about this part of the world.
The Bearing to Yerushalayim and Zmanim Map was recently updated to version 3.0. This new release adds a number of new features to the Zmanim Map version 2.0 update released in March 2010. The main change was updating the Google Map API version from the deprecated v2 to v3. This change increases performance and adds much better support for mobile browsers. The upgrade also means that a Google Maps API key is no longer required. This makes it easy to drop it into any site without any configuration (contact me for details). The technical notes on the original Technical Information about the Bearing to Yerushalayim Map post are still relevant, with very little having changed since the initial implementation.
The following is a partial list of the new features:
A link to download a 12 month Zmanim calendar directly from the map (using the same spreadsheet used in the Zmanim Calendar Generator). Clicking on the link from the Zmanim tab will generate a calendar with most typically used zmanim, while clicking on the link in the More Zmanim tab will download the full set of zmanim. These are available as the Calendar Type option in the Zmanim Calendar Generator
Increased use of jQuery and jQuery UI for formatting the zmanim tables to better match the site look & feel
Refactoring to make the code more robust and slightly more maintainable
Timezones for all of Israel now display the timezone of Asia/Jerusalem as opposed to the Asia/Gaza returned for parts of Israel by the GeoNames TimeZone web service
From a technical perspective there were a number of changes required due to updating the Google Maps API from v2 to v3. These include:
Renaming of a number of classes and functions such as GLatLng to LatLng
A number of functions that were part of API v2 were removed in v3. One example is the removal of radians in the LatLng that had been available and was replaced by the google.maps.LatLng class. These missing functions required for the direction to Yerushalayim calculations are now supported in the Zmanim Map using prototypes
As mentioned briefly in the “Why Some Zmanim Never Occur” post, the Lubavitch Jewish Center of Anchorage, Alaska has an interesting davening direction question. As explained in the “Bearing to Yerushalayim and Zmanim Map” (additional technical information is available in the “Technical Information about the Bearing to Yerushalayim Map” post), there are two opinions about the proper direction to face during Tfilah. The Levush and others are of the opinion that one should face the rhumb line direction to Yerushalayim, while the Emunas Chachamim and others are of the opinion that one should face the initial bearing of the great circle route. Both of these opinions would clearly use the shortest rhumb or great circle lines to Yerushalayim. As an example, a person standing on Har Hazaisim a mile east of Har Habayis would not daven east using the logic that continuing east for approximately 21,175 miles would reach Yerushalayim via global circumnavigation, when Har Habayis is just one mile west of him. The shul in Anchorage is located at a longitude of -149.86042°. The antipode of Har Habayis is on the -144.764851 longitude line – 180° of longitude from Har Habayis. People on different sides of this line will daven in opposite directions. Anchorage with a longitude of -149.86042° is 169.69 miles (273.1 km) west of the the -144.764851° longitude line. For this reason, the shul should daven not east, but west (255.78° from the north, or slightly south-west) if using the common rhumb line calculation, or north (355.67° from the north, or slightly west of north) if using the great circle calculation. Alaska is the only location in the world that has the -144.764851° longitude line cut across dry land, and is therefore the only non-ocean location to face this issue.
Notes: 1. Based on a rhumb line along the 31° 50′circle of latitude as opposed to 24,901 miles at the equator) using a WGS84Reference ellipsoid. 2. Rhumb line calculation as calculated by Movable Type using the same latitude for both points. The ellipsoidal shape of the earth is factored into this calculation. The short distance means that the 169.66 (272.98 km) great circle distance is very close to the rhumb line distance.
Why do Some Zmanim Never Occur in Some Locations? (Developers Beware)
While most people realize that the sun may not rise or set in the Arctic and Antarctic Circles (see the Star-K’s When Does One Pray When There Is No Day), many are not aware that some twilight dips will not occur during part of the year as far south of the Arctic Circle as London. For example around the summer solstice in London (on the zmanim map) the sun will never dip far enough below the horizon to reach Alos 16°. This happens in London from June 5th till July 8th. The image seen on the top right (original at timeanddate.com) shows various civil twilights centered on London on Midnight June 21st. Look carefully to see the various bands of twilight. Gateshead will not have Alos 16° from May 16th through July 28th, while Anchorage, Alaska (yes there is a Frum Shul in Anchorage with an interesting davening direction issue that is discussed in the Davening Direction from Alaska post ) will not have Alos 16.1° from April 25th to August 20th. Zmanim based on sunrise such as Also 72 that is a 72 minute offset of sunrise can be calculated as long as sunrise can be calculated, something that will happen as long as you are not in the Arctic or Antarctic Circles. For this reason, the Zmanim API will return a null when a zman will not happen. A Long.MIN_VALUE will be returned when a long is expected such as in the case of a Shaah Zmanis. While an inconvenience to developers who have to code for this, the alternative of a default date would mean that developers unaware of this would return incorrect zmanim, something far worse than a program error from a NullPointerException. In recent weeks two publicly available programs using the Zmanim API ran into issues due to nulls returned for early alos times. Being something not anticipated by the developers, the nulls generated errors in the programs that quickly led to fixes. For this reason Yitzchok updated the Zmanim .NET project to return the nullable DateTime? instead of the regular DateTime that it had previously been returning. While the Zmanim API documentation always made the possibility of a null being returned possible, I modified the documentation to make this clear on the return value documentation for every zman. Code with the modified documentation was part of the recently released Zmanim API 1.2.1.