An 8th magnitude plume is about 100 times too faint even for a good telescope. According to Goldstein, theoretical calculations of the debris plume's brightness shouldn't be taken too seriously. It's difficult to estimate precisely how much debris will be in the plume, how high the plume might rise, and what the reflectivity and sizes of the dust particles might be. It's conceivable that the debris plume could be much dimmer or much brighter than expected. A frame from a 2MB MPG animation of the scheduled crash from the UT Austin Lunar Prospector Impact Page Undaunted by the slim prospects for a detection, hundreds of amateur astronomers plan to monitor the Moon for signs of impact early Saturday morning.
Many amateurs are highly skilled and respected observers.
With fast-improving CCD and video imaging technology at affordable prices, they have access to equipment which rivals that found in many professional observatories. If a unexpectedly bright plume arises, amateurs somewhere will almost certainly record it. The impact will not be visible to the naked eye. Dry air observing sites are best. If the air is humid it will scatter the moonlight, greatly increasing the brightness of the sky, and making a faint plume that much more difficult to see.