Yesterday or thereabouts is the anniversary of the Buddha's parinibbāna.
Traditionally, in Theravāda countries, this event is commemorated on Vesak, but the Pāli texts indicate that the event actually took place in this month, most probably during the new moon.
9. When this was said, the Blessed One spoke to Māra,
the Evil One, saying: "Do not trouble yourself, Evil One. Before long the Parinibbana of the Tathagata will come about. Three months hence the Tathagata will utterly pass away."
This conversation with Māra took place during the last Rainy Season that the Buddha spent together with Venerable Ānanda. It was not at the beginning of the Rains, because at that time the Buddha was ill, and only later recovered his health by using meditation. The next event in the Sutta is the assembling of the bhikkhus from around Vesalī at the end of the Rains, and the Buddha's announcement to them that he would pass away in three months. Three months from the last month of the Rains (October) is sometime in January. I say it was probably the new moon rather than the full moon, because the Buddha's statement to Māra was apparently made before the end of the Rains, and because the new moon is a low point during the darkest and coldest month of the year in India.