Unfortunately, you’d be completely mistaken. ‘Ostara’ is an entirely modern celebration and was created in the last century by neopagans. The Spring Equinox was not celebrated in the Anglo-Saxon pagan calendar.
So, if we want to get all reconstructionist, when WERE Eostre’s feast days?
Going by Bede’s testimony, we know that the Anglo-Saxons divided the year into two halves, winter and summer. They employed a lunisolar calendar. Each year was bracketed by the winter solstice, falling approximately at December 25th on which a festival called Modranecht (Mothers’ Night) was celebrated. Each solar year contained either twelve or thirteen lunar months, with the new moon signalling the beginning of a given lunar month. Because you can’t neatly fit lunar months into a solar year, it was necessary to count an extra month in some years, a 'third Litha'; this was referred to as an embolismic month.
This article is one of the best breakdowns I’ve seen of how the Anglo-Saxon calendar worked.
The intriguing thing about the Anglo-Saxon summer and winter periods is how they were separated. We know from Bede that the formal beginning of the winter half of the year was the full moon of the month of Winterfilleth. Modern people might tend to imagine that the Autumn Equinox would be the natural point at which to mark the switch, but Bede explicity says otherwise. The very name ‘Winterfilleth’ refers to the tradition of marking winter’s beginning by the full moon of a given lunation.
Now, one thing we can readily observe about the Anglo-Saxon calendar is its symmetry. In the midst of the winter half of the year are two months called ‘Fore Yule’ and ‘After Yule’, while in the midst of the summer half are ‘Fore Litha’ and ‘After Litha’. (One month is not before a given event and the other after it; the sense is more that the former month is the first half of a given timespan, the latter the second half.)
Therefore, given that winter began with the full moon of Winterfilleth, we can speculate that summer began with the full moon of the month diametrically opposite to Winterfilleth in the calendar; and fortunately for our speculative reconstruction, the month in question is Eosturmonath, the month in which Bede claims feasts were held in Eostre’s honour.
This gives us a rather exciting platform from which to work. If Eostre’s festival took place during the full moon of Eosturmonath, we immediately have an explanation for why it involved ‘feasts’ as opposed to a single feast; the full moon lasts for multiple days. In addition, the festival would be in celebration of a calendrical event – the formal beginning of summer – as well as being in honour of a Goddess whose name is cognate with terms meaning opening and dawn.
It is also possible to see an Eostre-festival in a sceptical light, as the celebration of summer’s beginning with no reference to a Goddess at all (outside of Bede’s habit of imaginative speculation). Bede tells us of Winterfilleth only that it was observed, without reference to any deities. The full moons of Eosturmonath and Winterfilleth may therefore have been two calendrical events that were marked in a wholly secular way.
Personally, however, I like to imagine that the full moon of Eosturmonath really did signal the feast of a Goddess called Eostre and the beginning of summer; if nothing else, it is always fun to brandish such things in the face of those who celebrate an unhistorical and artificial Spring Equinox festival called Ostara. Much like the Roman Church of old, which was furious at the Ionian Church for celebrating Easter on the ‘incorrect’ date, we can lift up our voices and cry as one: you’re doing it wrong!
Next Easter Rant: The Case for Eostre, part 1 - The Eostur Sacrifice