A Halo Around the Sun Is Made of Ice Crystals
A halo is a ring of light. The atmospheric version has a precise and predictable radius.
A halo is a ring of light, in art around a holy figure and in the sky around the sun or moon. The atmospheric halo has a fixed size: ice crystals in high cloud are six-sided, and light passing through two of their faces bends by about 22 degrees, so the ring always appears at that radius. Hold out an arm and a spread hand roughly spans it. Greek *halos* originally meant a threshing floor, a circular area where oxen walked in a ring.
- A ring of light. *A halo round the moon.*
- A saint's nimbus. *A painted halo.*
- Halo effect — a bias. *The halo effect.*
- 22 degrees. *The standard radius.*
- Greek — *halos*, a threshing floor. *The root.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | halo | A halo. |
| Plural | halos | Halos. |
| Variant | haloes | Haloes. |
| Related | nimbus | A nimbus. |
| Greek | halos | A threshing floor. |
- A halo circled the moon.Sky.
- The saint has a gold halo.Art.
- The radius is 22 degrees.Optics.
Why the halo is always the same size
- Ice crystals in cirrus cloud are hexagonal
- Light entering one face and leaving another bends by at least 22 degrees
- That minimum angle is where light piles up brightest
- So the ring appears at a fixed radius regardless of conditions
- A rarer 46 degree halo forms through a different pair of faces
Greek *halos*, a disc or threshing floor, through Latin *halo*.
Why is a solar halo always the same size?
Because hexagonal ice crystals bend light by a minimum of 22 degrees, and that is where the light concentrates into a visible ring.
What is the halo effect?
A bias where one good quality makes people assume others. The name comes from the saint's halo lending a general glow.