Take the Earth-Moon system as we know it. Now, something causes a large rock to be lobbed in the direction of our moon. Exactly how that happens is deliberately left unspecified; it could be everything from an Earth-Mars war, to a rogue planet passing through the solar system, to something else entirely.
The impact should be sufficiently energetic to cause the resulting ejecta plume to be clearly visible from Earth to any creature with human-like vision who happens to be looking Moonward at the time. Let's put the lower limit for this at a plume height of about 10% of the angle subtended by the Moon itself as viewed from Earth at the maximum height where there is still a reasonable particle density. Bonus points to answers taking into account albedo and particle density, but that's not required.
You may choose the time, point and angle of impact arbitrarily, as long as the condition of visibility from Earth is met. (So hitting the back side of the Moon probably won't do it, but you are free to hit the Apennines from the side if you want to.) I'm thinking a direct hit near the terminator near full moon, but if something else works then feel free. I'm hoping for the spectacular effect, which is why I'm not fixating on any particular location.
You can assume that humans do nothing to counter the threat of an approaching large space rock; as to why, there is every reason from technical or physical inability to international politics or that humans are long gone from the planet.
With the preliminaries out of the way, two very much related questions:
What impactor parameters could give this short-term effect? Impactor mass, velocity (relative to the Moon), strike angle, location if relevant, any other relevant parameters I'm not thinking of?
Will the Moon likely survive the impact in the medium term? Said in one other way, is the impact energy comfortably below the gravitational binding energy of the Moon (which is approximately $1.24 \times 10^{29}$ J)? You don't need to worry about the effect of the impact on the Moon's orbit.