There are now 3 native iPhone programs in the iPhone App Store that display Zmanim. Pocket Luach from Tebeka Software, Zmanim from Avi Shevin and the iPhone Siddur from Rusty Brick. It is interesting to note that 2 out of the 3 use an open source Zmanim library. Zmanim uses Ken Bloom’s zmanim code the optional ZmanimCalculator (since replaced by the SunTimesCalculator) module in our Zmanim API uses a Java port of Ken’s code), and the iPhone Siddur uses a port of our own KosherJava Zmanim API (as mentioned in an email from the developer). With all of these available (and I am sure there are more to come), I am abandoning the iZmanim project to build a zmanim UI for the iPhone, since there is little need for it. My effort will concentrate on enhancing the API itself. I hope to be able to release the Rusty Brick Objective-C port of the API in the near future.
How are Zmanim calculations affected by the leap second?
Suppose prior to the announcement of the leap second, you had determined in advance that a given zman on January 15th, ’09 is 9:40:37 AM. Subsequent to that calculation having been made, the IERS decided to add a second to the clock. On January 15th, 9:40:37 AM is what would have been, 9:40:38 AM had the leap second not been added on 12/31. So taking into account the new leap second, the zman should be republished as 9:40:36 AM (which had there been no leap second, would have been 9:40:37 AM.)
Joseph,
You bring up an interesting but hypothetical question regarding the leap second. First, please do not rely on any zmanim down to the second. As mentioned a few times, atmospheric conditions can cause zmanim to be off by up to 2 minutes. In addition, zmanim calculations do not in general use a proper ellipsoid model of the earth, resulting in a somewhat “rounded number”. Even with all these inaccuracies, we have had user reports of “spot on” calculations in the Arctic Circle, an area notorious for difficulties in such calculations. That aside, the leap second would make no difference to zmanim. The leap second is meant to bring our clock back to mean solar time, in other words, it is meant to adjust an “inaccuracy” in our clocks VS solar time. This means that the zmanim calculations are for the most part accurate, but your clock is not :).
“That aside, the leap second would make no difference to zmanim. The leap second is meant to bring our clock back to mean solar time, in other words, it is meant to adjust an “inaccuracy” in our clocks VS solar time. This means that the zmanim calculations are for the most part accurate, but your clock is not :).”
Thank you for the feedback.
Nevertheless, the timing of when the leap second was issued was made somewhat arbitrarily. The International Earth Rotation and Reference Systems Service that determines these matters, could just as easily have decided to “catch up” 6 months earlier or 6 months later than 12/31/08. As such, the zmanim that are published seemingly would need to somehow take into account when the leap second is actually enacted by the IERS. In other words, it seems illogical to say that if the IERS had found it more convenient to enact the leap second on 6/30/09 (rather than 12/31/08), that it would make no difference on the published Zmanim between 1/1/09 and 6/30/09. The Zmanim would be off by one second in these two scenarios during those 6 months. (The IERS only enacts a leap second on either 6/30 or 12/31, and enacts it irregularly between as soon as 12 months apart or as long as 7 years apart, and typically announces it about 5 months in advance.)
Additionally, it appears that despite the astronomical reasoning for enacting a leap second, the zmanim were determined without anticipating any leap seconds (if someone obtained a post-Jan. 1st zman prior to the announcement of the leap second.)
As an aside, to help put the “arbitrariness” that I am referencing in perspective, there is currently a proposal pending before the IERS to abolish leap seconds and instead establish a leap minute that would only be necessary once in approximately 100 years. There is a realistic possibility this will pass within the next few years. Should this occur, would you still maintain your position? If not, would zmanim calculations then have to manually account for the fact that leap seconds are not being added except for once in about a century?
Joseph,
If I understand correctly, leap seconds nor leap minutes will ever be a problem when calculating Zmanim. Zmanim are always calculated independent of any clock. The purpose of leap seconds (and/or minutes) is to bring our clocks in tune with “solar time”, if you will. It’s not the Sun that’s changing, it’s our perception of what time it should be. Thus, the Zman is always correct (for a given definition of “correct”), and it’s our clock that is wrong.
The “issue” of leap seconds was covered in a standalone post FAQ: Zmanim and Leap Seconds.