↑ In pre-modern times, days were measured either from sunset to sunset, or from sunrise to sunrise, so that the length of the week (and the day) would be subject to slight variations depending upon the time of year and the observer's geographical latitude.
↑ Richards, E. G. (2013). "Calendars". In S. E. Urban & P. K. Seidelmann, eds. Explanatory Supplement to the Astronomical Almanac, 3rd ed. (pp. 585–624). Mill Valley, Calif.: University Science Books. 2013, pp. 592, 618.This is equivalent to saying that JD0, i.e. 1 January 4713 BC of the proleptic Julian calendar, was a Monday.
1 2 sennight at worldwidewords.org (retrieved 12 January 2017)
