
Originally Posted by
Attiyah Zahdeh
http://apod.nasa.gov/apod/ap990625.html
Explanation: If you look carefully enough, you can even see the glow of the Sun in the opposite direction. At night this glow is known as the gegenschein (German for "counter glow"), and can be seen as a faint glow in an extremely dark sky, as pictured above. The gegenschein is sunlight back-scattered off small dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets. The gegenschein is distinguished from zodiacal light by the high angle of reflection. At day, a phenomenon similar to the gegenschien called the glory can be seen in clouds opposite the Sun from an airplane.
How do NASA's scientists justify that the asteroids themselves couldn't be seen by the naked eye while a dust splintered from them could be seen?
As already mentioned several times: Pictures alone are not evidence. Even more so, when you don't know how they are taken or processed.
If you break up an astroid in many pieces, the sum surface is much larger. This is why it is easier to see. Most of the material is inside or on the opposite side of the asteroid. Of course, you don't see a single dust grain, but millions of them are easy. It is also a matter of size of the particles that can be much smaller than millimetres. The closer the size of the particles reaches the wavelength of the scattered light, the more efficient it is. This applies to the zodiacal light and the gegenschein. Zodiacal light analogues have been observed numerous times toward dust discs around young stars. Explain: Why is it, that mist and fog are seen more easily (even on large distances) than their condesend equivalent of a bucket full of water?
Ah, and by the way: please note that NASA is not the only astronomical organisation in the world. Their interest is manifold, one of which is attract public interest by pretty pictures.