This article was regrettably very necessary. Errors on the topic of zemanim proliferated in the halakhic literature. Yet worse, trying to integrate errored views led to yet more significant errors. The article below attempts to classify errors into 6 categories with examples per category. I would appreciate comments on the individual errors and the method chosen for categorization.

While many errors did not immediately lead to badly errored pesakim, their use by others may not have been so fortunate. One example suffices to illustrate the issue. As we can now very precisely calculate, the period between sunset and the day’s end varies by both distance from the equator and the time of year. Early in (modern) halakhic history (17th century,) Rav Avraham Pimential errored when he equated that variation to the length of the day, sunrise to sunset. While his formula is imprecise during the summer, it is entirely incorrect in the winter. Intuition or some might argue, siyatta di’shemaya, led him to caution against the use of his formula in the winter. Given his prominence, that error, together with his caution, is still to be found in the rabbinic literature. Now, however, we also have a prominent congregation and its well-respected Rabbi using something that appears remarkably similar just last winter on their website.