I agree with Ouroboros.
Is it desirable for those durations to be set in stone? Is it desirable to use up the precious space in a rule book for those clarifications. It will take space. It's not as simple as "when the sun is fully visible", or "when a beam of the sun is visible", etc. Clouds on the horizon, in caves, mountains, towers, valleys, etc.
Let's consider the duration issues.
The Parma drops for a certain time each morning. The magi are vulnerable and it probably terrifies many of them. When that time is; when a sliver of the sun is seen, when the sun is visible, is near irrelevant. If a player or SG wants to exploit when the Parma or sun spells finish, they can.
For year spells, it gives the SG freedom, especially regarding the Aegis. If year ends on dawn of the day it's cast, then the Aegis is down when being cast, which brings risk. If the SG does not want that risk in their game, the SG decides a year is the end of the day it is cast so the Aegis is always there.
The SG sets the rules. An NPC opponent and a PC both know when the spell ends and plan accordingly. Is it 2 minutes (diameter) early or later is near meaningless. Is the light quality going to be that different in 2 minutes, are their any other meaningful factors?
The only time those finely nuanced duration interpretations will matter is when the SG decides they will. If your SG decides magic will hit you when your parma is down, it will happen.
But does it? There's the rub.
I seem to recall that in a previous edition there was a small overlap between day and night that guaranteed that you could keep your parma protection always active as long as you were not interrupted more than a handful of rounds at dawn and dusk. You seem to take for granted there's actually a gap of several rounds at dawn and dusk when a magus will be inevitably exposed, no matter how careful he is.
This is a much more crucial detail to clarify than whether the Aegis needs to penetrate or not, whether there's a "flicker" in D:Sun effects produced by items, and whether an invisible character still casts a shadow. It dramatically changes how magi go adventuring in supernatural locales or wage wizard wars.
I think that the argument "it should be left vague so the SG can decide" has no merit. Why spell out the Limits of Magic, the duration of Twilight, the sterility engendered by Longevity Rituals or the effects of spell Mastery then? Why give rules at all? Let's just give the setting and let the SG decide! The issue is that a troupe can always decide. But they should have something to default to, with the guarantee that if they stick to it everything will work and the setting still makes sense. This saves effort and arguments.
Lack of rule support is not freedom, because the troupe can always make a conscious decision to override a rule. But it makes for arguments at the gaming table, and it devalues material for the line because you don't know under what assumptions it's been written - would the King Fir plot in GoTF still make sense if the Aegis had a time gap?
There has been a major shift in what is being asked over the course of about two posts, from "When exactly is sunrise/sunset?" to "Can you keep a Sun/Moon/Year Duration effect up constantly if you have the opportunity to recast?". An answer to the first would answer (part of) the second, but you can answer the second without answering the first.
I think answering the first question is a really bad idea, for the reasons I gave and an additional one. The additional reason is that Ars Magica RDTs are supposed to get away from wargaming measurements. This is part of the flavour of Hermetic magic. Giving precise-to-the-second definitions of their endpoints would undermine that.
The second question, however, can be answered. The assumption has always been that continuity can be achieved in normal circumstances, so there is no harm in making that explicit. The details of exactly how and why that works can be left up to individual troupes.
Having actually tried it, even this is a bit involved. How about the following?
A magus can recast a spell with Diameter, Sun, Moon, or Year Duration at the end of its period, so that the effect is continuous, and does not briefly disappear between the two castings. The magus recasting the spell does not have to be the same person who case the original spell, and it does not even have to be the same spell, although for a lot of spells an overlap will not make much difference. (This is important, for example, if a covenant casts a higher-level version of Aegis of the Hearth one year.) No roll is required to achieve this, but distracting events may prevent it. The critical period is about a Diameter for Sun, Moon, or Year spells, and any distraction that interrupts the recasting of the spell is enough to guarantee at least a short break for Diameter spells. For Ritual spells, it is easy for magi to determine when they must start casting to avoid a break, as such calculations are covered by Artes Liberales and Philosophiae, but if the Ritual is interrupted and must be restarted, there not be enough time to restart that Ritual and cast it before the older spell ends.
Thanks. Nice clarification.
I should consult the rule book before every time I post. Twice in recent days I've made a wrong assumption. The parma and aegis can be continuously maintained without house ruling it. Oops.
I can't remember whether this in included anywhere in the rules at the moment, but a statement that magi can generally judge how long a diameter is, whether something is sufficiently circle-like, how far their voice will carry &c as to be able to effectively use magic would be useful. that is, something to the effect that there's no ambiguity on how spells will function under normal circumstances.
I really just wanted an answer to the second; I agree that the first is best left unanswered. Thanks!
The critical period is about a Diameter for Sun, Moon, or Year spells, and any distraction that interrupts the recasting of the spell is enough to guarantee at least a short break for Diameter spells.
This is the only part that gave me thought.
For D:Sun (including Parma) I completely agree with "the critical period is about a Diameter".
For D:Moon and particularly D:Year ... I'd probably like something longer? It just feels everything has to be a bit too "precise" (and raises the question; can a magus keep up his Parma and reraise the Aegis)?
For D:Diameter, I was about to say I was not sure whether the issue is meaningful because D:Diam does not align to an external astrological event: if you cast a D:Diam spell a round later, it expires one round later (which is not true of other durations). I guess what was meant was: you can carefully string together a sequence of X D:Diam spells, so that they cover a time interval of X Diameters, and there is no discontinuity in their effects. But since D:Diam is a bit vague anyways ... Still, I like more info than less info!
On the other hand it would be nice to clarify what happens with D:Mom too, which from the examples can last about a round or even a little longer. I think that if a magus does nothing else but recast D:Mom spells, he can maintain "spell continuity". If that's the case, adding D:Mom to D:Diam in the text would be a minimal change that still provides useful info.
I thought everyone in all games conveniently ignored the complexity of working out range, duration etc, as we don't wont the consequences of delving too deep in it.
With all the movement in a conflict, what is realistically the chance of getting the angle, the positioning perfectly right? Blasting a spell past an ally to hit an enemy, an explosion hitting the enemy but ceasing just before an ally, perfectly positioning a spell to hit a person and a person in a direct line behind them, hitting an enemy at the exact point 1 millimetre before the spell ends. Any duration, if one doesn't have a watch, good luck with that.
I'm not just talking Ars Majica here. People play games for fun. A spell missing because the delivery angle was off by 5 degrees, is not fun. Having to make a roll every time one casts a spell to see if it's positioned correctly, not fun.
The average person can't know exactly how far 50 paces are by eyeballing it. At the same time, we shouldn't think the spell will work at full potency at one point, and then because someone takes a step back, it fails. If someone is thinking of casting a voice range spell and thought it might be too far, they'd take a few steps forward, or if someone is charging at them, wait a second or so.
That was my instinct as well, but the rules specify that the durations end at sunrise/moonrise, so we are kinda stuck with it. I think this also does a better job of creating dramatic possibilities.
In answer to the question: The way the vagueness works suggests that the answer is "yes, but it is tight".
That makes no sense for too many Mom spells for a rule, I think. The analogy should work for the cases where it does make sense.
However, I think it might bear repeating in (or near) the Targets & Size box (p. 113).
That, or perhaps there needs to be some reference from there to the definition of Size.
Simply put, there's a lot of people who haven't noticed it.
I love this! This is such a nice clarification/addition. The idea that there can be enough overlap that casters aren't weakened or disadvantaged is a great one. So yeah, thumbs up on this.
Okay, I know this is an old conversation. I don't spend a lot of time on this forum, and I stumbled onto this thread from Googling for something unrelated--so I apologize for the all the notifications people will get. Me culpa.
To answer David Chart's question about hard-to-find rules:
The rule that Encumbrance is subtracted from Casting Totals is on page 178 in the Encumbrance section, not mentioned on page 81 where Casting Totals are introduced.
Way back when dinosaurs walked the Earth, I read the first ed ArM rules and was struck by the elegance of that mechanic. For over a decade, D&D players had been asking "Why can't my Magic-User wear armor?" and DMs had been saying, "You just can't." And with a simple provision, Ars Magica explained why magi don't (usually) wear armor.
The thing is--because of the penalty existing, it rarely came up. The second edition omitted it--not as an intentional change, but because the editors forgot it (until I wrote to them and pointed it out).
I've recently run into ArM5 players who had no idea that rule exists--because it's buried ...