Mir contains about 18 heavy metal flywheels called gyrodynes, turned by electric motors and thus able to control the pointing of Mir in operation. These with the docking adapters and the many 75 kg nickel cadmium batteries are the heaviest items, and will be the last to slow down, thus travelling to the east end of the debris footprint. Cooling down, they will not be glowing, and will be hard to see, even in daylight. Heavy parts take longer to burn away, but their inertia means they also take longer to slow down, being exposed to the flame for a longer time. In total, about 35 tons of the original 137 tons is estimated to reach the surface.
Strong candidates are the gyrodynes, batteries, tanks, and docking adapters.
An American group led by Bob Citron of Spacehab is planning a flight from Tahiti to experience the re-entry at first hand. Because of the unknowns and the need to keep their distance, their chances of seeing anything are doubtful. They plan talks by Mir veterans and live video linkups to celebrate the event. People on the surface or in the air near the re-entry track will also be treated to a light and sound show. Best light effects will be around 80-50 km altitude.