22 degree halo

JUN 11

Preliminary   > Science and Technology   >   Miscellaneous   >   Cosmology

Why in news?

  • A 22 degree halo was recently seen in Bengaluru.

About the Halo:

  • A 22° halo is an optical phenomenon that belongs to the family of ice-crystal halos.
  • Its form is a ring with an apparent radius of approximately 22° around the Sun or Moon.
  • When visible around the Moon, it is called a moon ring or winter halo.
  • It forms as direct sunlight or moonlight is refracted in millions of hexagonal ice crystals suspended in the atmosphere.
  • The halo appears large; its radius is roughly the length of an outstretched hand at arm's length.
  • A 22° halo may be visible on as many as 100 days per year – much more frequently than rainbows.

Prelims Question

Consider the following statements regarding 22 degree halos:
1.It is a celestial phenomenon seen only in the north or south poles.
2.It is caused by presence of ice crystals in the atmosphere.
Which among the above statements is/are correct?
(a)1 only 
(b)2 only
(c)Both 1 and 2
(d)Neither 1 nor 2

Answer to prelims question