Asteroid
The dwarf planet Ceres is by far the largest asteroid, with a diameter of . The next largest are 4 Vesta and 2 Pallas, both with diameters of just over . Vesta is the only main-belt asteroid that can, on occasion, be visible to the naked eye. On some rare occasions, a near-Earth asteroid may briefly become visible without technical aid; see 99942 Apophis.
Near-Earth object
Two of the biggest Near-Earth objects 433 Eros and 1036 Ganymed, were also some the earliest to be detected. 1036 Ganymed is about 20 miles in diameter. As bigger asteroids they reflected more light. One way around simply finding the NEOs that reflect the most visible light, is to use infrared telescopes that observe the objects heat emissions.