In many traditions, the annual cycle of the calendar is considered to start with the coming of the season of Spring. In ancient times in Europe, the year was commonly divided into eight more or less equal parts dedicated to the different activities appropriate to the time of year. The transition from one part to another was traditionally marked with festivities, thanksgiving for past blessings and prayer for continued wellbeing.
This cycle of eight annual festivals, four major and four minor, is preserved in its most pure form in Celtic tradition, which is why they are now customarily known by their Celtic names in communities as diverse as Druids, Wiccans and Ceremonial Magicians.
In early Christian times, the traditional festivals were absorbed into the Church calendar. This should not be seen as an attempt by the Christian Church to suppress "pagan superstitions", but rather a recognition of the fact that it is only right and proper at certain points in the year to celebrate God's gifts to us throughout the year. Furthermore, the Church calendar is important, because it gives us a clear indication of the days in the year when the traditional festivals were actually celebrated.
To preserve an ancient tradition might be reason enough. But more importantly, certain times of year are more conducive to the exercise of meditative, prayerful and, yes, magical activities for particular purposes than are others. The reasons may well be partly psychological, but they are none the less powerful for that. They are also potent reminders of our fundamental connectivity with our environment, the Earth on which we live and which gives us sustenance. The fact that other people of like mind will be performing similar exercises at the same time make the experience even more intense and productive.
Those who have astrological inclinations and a tidy mind like to celebrate the festivals at precise points of the Sun's progress through the Zodiac during the course of the year, starting with the beginning of Spring when the Sun enters the Zodiac sign of Aries. However, the traditional dates do vary from this somewhat; in many cases celebrants will use the traditional dates simply because that is when the majority of people will be celebrating. If you live in a predominantly Christian country, it would be almost perverse not to celebrate the Yule festival on Christmas Day, when so many other people around you are holding their own celebrations - and doing so, whether they realize it or not, for reasons very similar to your own.
But, actually, you must do what feels most comfortable to you. It may simply not be practicable to perform your meditation on the precise day. A few days either way will not matter. It is best (but by no means essential) if you can choose a day when you know many other people will be celebrating; which is why I tend to prefer the traditional days of celebration, which are well known to many.
One more point: traditionally, the Day, and hence the Festivities, start at the previous sunset. Thus, for example, if the Yule festival is to be celebrated on Christmas Day, celebration will actually commence at sunset on Christmas Eve. However, if you choose to celebrate the astrological event, you should celebrate as near to the exact time of the event as practicable. The times in the tables below are given in Terrestrial Time, which is approximately the same as GMT: the small difference can be neglected for our present purposes.
You would still agree that Christmas falls in December, would you not? Use the dates for the festivals as given, without modification for the seasons of your country. You will then be tuning into the same energies as others of like mind throughout the World, at the same point of the year as them.
Traditional: Annunciation (Lady Day), March 25th.
However, some prefer to celebrate Ostara at Easter; the name itself gives an obvious indication of an historical link. Easter Day is notionally the first Sunday after the first Full Moon after the Vernal Equinox: traditionally coinciding with the Jewish Passover. However, owing to variations in the way the date is calculated, Easter Day varies in different branches of the Christian Church and may or may not coincide with the actual Passover. The following dates are correct for the Western Christian Churches (Catholic and Protestant). The Eastern (Orthodox) and Coptic Churches use their own calendars.
Astrological: Vernal Equinox, Sun 0° AriesDates for coming years:
Traditional: May Day, May 1st.
Astrological: Sun 15° TaurusDates for coming years:
Traditional: St John the Baptist (Midsummers Day), June 24th.
Astrological: Summer Solstice, Sun 0° CancerDates for coming years:
Traditional: Lammas, August 1st.
Astrological: Sun 15° LeoDates for coming years:
Traditional: St Michael and all Angels (Michaelmas), September 29th.
Astrological: Autumnal Equinox, Sun 0° LibraDates for coming years:
Traditional: All Saints' Day (Hallowmas), November 1st.
Astrological: Sun 15° ScorpioDates for coming years:
Traditional: Christmas Day, December 25th.
Astrological: Winter Solstice, Sun 0° CapricornDates for coming years:
Traditional: Presentation of Christ (Purification or Candlemas), February 2nd.
Astrological: Sun 15° AquariusDates for coming years: