 Prof. Dr. Stöckl, a meteorologist from Regensburg, also proposed a similar theory and made similar observations.Critics also suggest that a combination of clouds, atmospheric effects and natural sunlight could have created the reported visual phenomena.Steuart Campbell, writing for the edition of "Journal of Meteorology" in 1989, postulated that a cloud of stratospheric dust changed the appearance of the Sun on 13 October, making it easy to look at, and causing it to "appear" to be yellow, blue, and violet, and to spin.