When the same diffraction effects occur in clouds some distance from the sun which are composed of tiny uniform droplets, colorful bands or "iridescence" can be seen. The corona around the sun is often hard to see because it is close to the sun and masked by the extreme brilliance of the sun. Remarkable telescoping of the shadow size occurred within the glory.Įxamples of glories on close and distant clouds At this point the aircraft shadow is larger than the glory, but as the clouds became more distant, the shadow was smaller while the glory stayed the same size. This glory was observed on an approach to Anchorage through clouds which were sometimes very close, sometimes distant. It is remarkable in that the second order diffraction is visible and a hint of third order.īelow are links to posted examples of glories: This photo of a glory was taken by Frank Starmer and is used by permission with all rights reserved to Frank. However,mathematical modeling of the details is quite complex. Mie scattering isthought to be themechanism controlling theintensity of lightscattered back tothe viewer. A small opaque circular scatterer gives a diffraction pattern like that of an aperture of the same size. The nature of the diffraction is similar to aperture diffraction, but is diffraction from the water droplets in the cloud. The phenomenon is one of diffraction, with smaller droplets givinglarger glories. For more distant clouds, the plane's shadowwould be smaller, but the glory would be the same angular size if the waterdroplets were the same size. What size droplet would it take to diffract light at 22°?Ī rainbow band around the shadow of your aircraft seen on a cloud below is an example of a glory. The shorter wavelength blue light produces diffraction maxima closer to the sun. This indicates diffraction in tiny water droplets. The colors are subtle, but you can see a blue tint to the corona close to the moon and a reddening further out. The moon corona image above was taken on Maon a night when thin clouds were moving swiftly across the sky. The diffraction by a tiny opaque barrier shows the same pattern as that of an aperture of the same size and shape in an otherwise opaque screen (Babinet's principle). The appearance is often that of alternating blue-green and red circles. This circle is smaller, on the order of 10°, and is caused by diffraction of light by the small particles. A circle of light quite distinct from the 22° halo can sometimes be seen around the sun or moon if there are thin clouds composed of water droplets or ice crystals of nearly uniform size.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |