why is there a halo around the moon tonight

Even though it is one of the most common types of halo, the exact shape and orientation of the ice crystals responsible for the 22` halo are still the topic of debate. Hexagonal, randomly oriented columns are usually put forward as the most likely candidate, but this explanation presents problems, such as the fact that the aerodynamic properties of such crystals leads them to be oriented horizontally rather than randomly. Alternative explanations include the involvement of clusters of bullet-shaped ice columns. As light passes through the 60` apex angle of the hexagonal ice it is deflected twice resulting in deviation angles ranging from 22` to 50`.

The angle of minimum deviation is almost 22` (or more specifically 21. 84` on average; 21. 54` for red light and 22. 37` for blue light). This wavelength-dependent variation in refraction causes the inner edge of the circle to be reddish while the outer edge is bluish. The ice crystals in the clouds all deviate the light similarly, but only the ones from the specific ring at 22 degrees contribute to the effect for an observer at a set distance. As no light is refracted at angles smaller than 22`, the sky is darker inside the halo.

Another phenomenon resulting in a ring around the Sun or Moonand therefore sometimes confused with the 22` halois the. Unlike the 22` halo, however, it is produced by water droplets instead of ice crystals and it is much smaller and more colorful.
BUFFALO, N. Y. -- The moon appeared a bit different in the sky Monday night, surrounded by a gigantic bright halo. Storm Team 2 Meteorologist Heather Waldman says this is called a lunar halo. It's caused by millions of tiny ice crystals or water droplets in thin cirrus clouds.

Scientists refer to them as 22-degree halos because the ring appears about 22 degrees around the sun or moon. The clouds cause both refraction, or the splitting of light, and reflection, or glints of light from the ice crystals, according to the science radio show This phenomenon is also called a Lunar Corona. Although it's seen on clear nights, this halo often indicates that precipitation is on the way. Snow and rain is on the way for Tuesday and later this week. Here is the latest Storm Team 2 Forecast:

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