Shop Windows to the Universe

The Winter 2010 issue of The Earth Scientist includes a variety of educational resources, ranging from astronomy to glaciers. Check out the other publications and classroom materials in our online store.
Anti-crepuscular rays are beams of sunlight that appear to converge on a point opposite the sun. They are similar to crepuscular rays, but are seen opposite the sun in the sky. Anti-crepuscular rays are most frequently visible near sunrise or sunset. This photo of anti-crepuscular rays was taken at sunset in Boulder, Colorado. Crepuscular rays are usually much brighter than anti-crepuscular rays.
Click on image for full size
Image Courtesy of Carlye Calvin

Atmospheric Optics

Have you ever seen clouds in the sky that looked different than "normal" clouds? Or have you wondered why rainbows form? Sometimes there are phenomena in the sky that are affected by light and make clouds and the atmosphere look very colorful or unique. Atmospheric optics shows us how light behaves as it passes through the atmosphere. From rainbows to the northern lights, these optical features are dynamic and allow us to learn about atmospheric conditions. Some of these phenomena can be seen very often, and some are once in a lifetime sights.

In some instances, dust, small particles, and moisture droplets scatter light to make the sun's rays visible while clouds and mountain shadows are dark by comparison, creating crepuscular rays or anti-crepuscular rays. In other cases, air and very small particles can scatter colors selectively to make skies blue or sunsets appear to be on fire. Misty clouds and fog contain tiny water droplets that produce strange optical effects that are mostly ringed and brightly colored, including iridescent clouds and glory. Tiny ice crystals in the atmosphere can create halos by refracting and reflecting light.

There are many beautiful examples like these of light and color at work in the atmosphere. Visit the Photo Album of Atmospheric Optics and the Atmospheric Optics Image Gallery to see images of many types of these phenomena, as well as information on how they form.

Last modified February 10, 2009 by Becca Hatheway.

Shop Windows to the Universe Science Store!

Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Rainbows

Rainbows appear in the sky when there is bright sunlight and rain. Sunlight is known as visible or white light and is actually a mixture of colors. Rainbows result from the refraction and reflection of...more

Aerosols: Tiny Particulates in the Air

Aerosols, also called particulates, are tiny bits of solid or liquid suspended in the air. Some aerosols are so small that they are made only of a few molecules – so small that they are invisible because...more

Fog

Fog is a ground-level cloud. There are several ways that fog forms. It usually forms when moist air travels over cold land or water. The moist air cools down and the water vapor condenses and forms a cloud...more

Noctilucent Clouds

Noctilucent clouds (NLC’s) or polar mesospheric clouds (PMC’s) are found very high in the Earth's atmosphere (about 85,300 meters above the Earth's surface!). They are called Polar Mesospheric Clouds when...more

Altocumulus

Altocumulus clouds (weather symbol - Ac), are made primarily of liquid water and have a thickness of 1 km. They are part of the Middle Cloud group (2000-7000m up). They are grayish-white with one part...more

Altostratus

Altostratus clouds (weather symbol - As) consist of water and some ice crystals. They belong to the Middle Cloud group (2000-7000m up). An altostratus cloud usually covers the whole sky and has a gray...more

Cirrocumulus

Cirrocumulus clouds (weather symbol - Cc) are composed primarily of ice crystals and belong to the High Cloud group (5000-13000m). They are small rounded puffs that usually appear in long rows. Cirrocumulus...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA