brightest asteroid

The asteroid that appears brightest from Earth is 4 Vesta. When at its nearest to Earth, Vesta reaches magnitude 6.5. In very dark sky conditions it is just detectable to the naked eye. It is the only asteroid in principle visible to the naked eye. The next brightest, the largest asteroid Ceres, never exceeds magnitude 7.3. Though only three-fifths the size of Ceres, Vesta is far more reflective. It reflects about 25% of the sunlight falling on it, while Ceres reflects a mere 5%. Vesta appears to be unique among the larger asteroids, with a surface consisting of light coloured volcanic rocks, which account for its high reflectivity. The most reflective asteroids belong to a different class known as E-type (for enstatite). They are rare, and have reflectivities between 30 and 40%. The brightest of these is 44 Nysa, which reaches magnitude 9.7 though it is only 68 km across.