As hinted by C.E.B’s article, Pesach (Passover) and Sukkot (Festival of Booths) are Jewish holidays — two of the three major festivals — in the Jewish calendar. That calendar is a Lunar/Solar calendar that does not correspond with the Gregorian calendar, which is why which holiday dates vary each year in the Gregorian calendar. Watching and marking the phases of the moon is not all there is to the Jewish calendar.
Before the calendar’s calculations were settled by Hillel II in the fourth century the first sliver of the new moon was reported to the Sanhedrin. Based on the report of two witnesses who were both reliable and independent of each other the Sanhedrin declared it to be the first day of the month (Rosh Chodesh). A shofar (ram’s horn) was ritually blown and messengers carried the announcement. Rosh Chodesh is, after all, a festival day each month.
However, it is most important to understand that the Jewish calendar is not a lunar calendar. A lunar month is about 29.5 days. Twelve of them only amounts to 354 days so another 11 or 12 days or so would be needed to make it correspond with the 365.25 day solar year. The difference gets even worse when simplified too much by using 29 days instead of 29.5 days per lunar month. Without intercalated days to compensate for this difference the Torah-mandated seasonal (solar) holidays would be out of sync by nearly two weeks every year. Using a 13-month lunar year is just as bad in the other direction: too many days instead of too few. With ancient Jews spread throughout the world (diaspora) getting word of the new month from declarations by the Sanhedrin simply could not work. Hence, the Jewish calendar.
Taking C.E.B.’s assumption that ordering delivery of a current calendar may become difficult or even impossible in SHTF conditions lasting longer than a year, having personally printed copies of the Jewish calendar may be as important to many people as having hard copies of selected books instead of depending on PDFs or other electronic versions.
There are several Jewish perpetual calendar web sites one could go to generate and print several years of calendars. One great one I recommend is at HebCal.com. Aside from selecting the Gregorian or Hebrew calendar year to generate, selections exist to show holidays, Rosh Chodesh, fast days, special Shabbos days, and so on. It will also generate candle lighting times for your local zip code’s time zone. There are other options.
The web page with the calendar generated can be printed of course, but there are also download format options for Windows, Mac OS, Google Calendar, Yahoo! Calendar, and others. Furthermore, click the next month link or next year link at the top to advance the calendar for the next printout or download.
As for one last detail from C.E.B.’s article, it isn’t likely that those who pay attention will lose track of which day of the week it will be. The Jewish names of the weekdays were always First, Second, Third, Fourth, Fifth, Sixth, Shabbos! – Larry R.