These spectral measurements of the asteroid Eros were taken on December 23, 1998 from the Near Earth Asteroid Rendezvous (NEAR) spacecraft as it flew by the asteroid. The measurements were compiled from data taken by the multispectral imager over 5 hours surrounding the closest approach at 2375 miles (3830 kilometers) from the asteroid at 1:43 PM EST. Each spectrum is a measure of the fraction of sunlight of different wavelengths that is reflected by the asteroid. The images at right show the asteroid's appearance at the times of the measurements. Different minerals reflect sunlight with a different spectrum, providing a "fingerprint" of composition of the asteroid's surface. The progressive shift in the depth and position of the trough in Eros's spectrum (traced by the thin gray line) results from subtle changes in the mixture of minerals exposed on different parts of the asteroid.