Junctures are a poorly understood phenomenon. This has not been
helped by the fact that they haven't exactly been covered in any sort
of detail in any of the books. They are mentioned as special days in
which Quintessence flows more freely...But what exactly does this
mean? Are their just certain day in which Raw Q is just falling from
the skies like so much manna...?
Probably not. To my way of thinking, a Juncture is simply a day with certain sort of resonance that actually aids in the performance of magick with a similar resonance. Most junctures are fairly weak in these modern times and add nothing more than -1 to a magic roll (this usually requires some sort of High Ritual roll at an average difficulty.)
Some Junctures are more potent. These mystically charged days usually ends or beginings of seasonal cycles or have been holy days of some sort since time immemorial. Such a day might provide -2 or even -3 to a magic roll with an attendant high ritual roll. On these days it's even possible to lean into the resonance of the day without high ritual for a -1 on the roll. Such days are busy days for all mages.
Some Junctures are extremely potent affairs. These might happen every few years or decades or centuries and are usually a day when some sort of astrological phenomenon coincides with a day that is allready mystically charged. The effects of this are best left to the imagination of the ST but a good rule of thumb might be that magic with an appropriate resonance and a bit of high ritual might actually garner a free success on each magick roll. and that Magick of an antithetical resonance is at significant minuses. This sort of thing can get out of hand pretty quick so it is recommended that you use these sorts of Junctures sparingly.
Junctures also have another purpose. They are typically days set aside to revere spirits and heroes of the past and perhaps try to draw their favor in some way. This can run the gamut from sacrificing a black cock on a special day in order to draw the attention of one of the Loa to holding a feast to venerate saint in order to recieve that saints blessing. For mages, they take on an additional significance. Junctures offer the possibility to communicate with specific spirits and try to garner their favor on a day when they are especially favorably disposed. Garnering this favor might involve a few twists and turns and not all spirits would be interested in the same sort of tribute ( A feast on St Mark's feast day is going to be very different from trying to catch the favor of Lord Moloch.) This offers the players and the ST an interesting way of getting in touch with the spirit world that doesn't involve crossing the gauntlet (which is problematical anyway.) Most of these rituals still involve the use of Spirit 2 in order to use but it should be noted that even spirits that don't possess the charm Appear will be able to do so at a ritual consecrated to them on their juncture.
Naturally, This is not an excuse to meet all the luminaries of the spirit world without actually leaving your house. Most of the more powerful spirits cannot be summoned without use of far greater magick but this doesn't mean that they can't send an emissary.
Ex: Ariannae is a Verbena who has a particular affinity for Hellenic Magick and Athena in particular. Through a bit of research she finds that there was a particular day that Athena's temples received tribute. Gathering some sweetmeats and olives she burns them on her altar and throws some high ritual dice and some spirit 2 Mojo on it for flavor. Since Athena is still a god level muckety-muck, even if she is out of fashion, she does not show up herself. But she is pleased with the sacrifice and sends an Owl gaffling to bring it to her. The Owl is instructed that he is to give his summoning name to Ariannae and is to be her emissary to the goddess. The Sacrifice is changed into raw quintessence which the goddess shares with the emissary who then takes an interest in the affairs of the Verbena at the urging of his mistress. With this, Ariannae has gotten her foot in the door (spiritually speaking) and may proceed at a later date to fashion some sort of pact or covenant with the spirit and/or his mistress.This is a good way to meet familiars too.
Junctures have a 3rd purpose as well. Theurgically inclined mages can use the power of a days special resonance in order to attempt to cleanse unwanted resonances from a person ,place, or thing. Easter, and Yom Kippur are perfect examples of this type of day but many exist. The Mages often creates a ritual which involves a sacrifice made to cleanse some sort of spiritual taint. This may be as involved a catholic mass or as simple as fasting,prayer and study. Even really nasty forms of spiritual taint can be combatted in this way...as long as the petitioner is sincere and faithful. Heck it's even possible to develop True Faith (ask your ST first monkey-boy) By magickal tradition, those who are saddled with longer periods of atonement,(like Lent or Ramadan) will receive their benefits on the last day of that period.It should be noted though that longer attonements might garner more successes.
It should be noted that persons of a less than nice bent can also use this to their advantage. Fires happen on Devil's Night for a reason. Some of those fires are consecrated to the powers of strife and anarchy, and others just sort of happen in their wake.