What is Almanac?

Legal Definition
An almanac (also spelled almanack and almanach) is an annual publication that includes information such as weather forecasts, farmers' planting dates, tide tables, and tabular information often arranged according to the calendar. Astronomical data and various statistics are found in almanacs, such as the times of the rising and setting of the sun and moon, eclipses, hours of full tide, church festivals, and so on.
-- Wikipedia
Legal Definition
A table or calendar, in which are set down the revolutions of the seasons, the rising and setting of the sun, the phases of the moon, the most remarkable conjunctions, positions and phenomena of the heavenly bodies, the months of the year, the days of the month and week, and a variety of other matter.

2. The courts will take judicial notice of the almanac; for example, whether a certain day of the month was on a Sunday or not. Vin. Ab. h. t.; 6 Mod. 41; Cro. Eliz. 227, pl. 12; 12 Vin. Ab. Evidence (A, b, 4.) In dating instrments, some sects, the Quakers, for example, instead of writing January, February, March, &c., use the terms, First month, Second month, Third month, &c., and these are equally valid in such writings. Vide 1 Smith's Laws of Pennsylvania, 217.
-- Bouviers Law Dictionary
Legal Definition
A publication, in which is recounted the days of the week, month, and year, both common and particular, distinguishing the fasts, feasts, terms, etc., from the common days by proper marks, pointing out also the several changes of the moon, tides, eclipses, etc.
-- Black's Law Dictionary