Source: IndiaToday

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Context

• A rare celestial phenomenon known as a "double sun halo" was recently witnessed in the skies over Leh, Ladakh.
• This event captivated observers and provided a stunning display of concentric rings around the sun.

Details

What is a Double Sun Halo?

A double sun halo is a variation of the more common 22-degree halo. It consists of two halos:

1. Inner Halo: A bright ring with a radius of approximately 22 degrees from the sun.
2. Outer Halo: A larger ring with a radius of around 46 degrees from the sun's center.

Formation of the Double Sun Halo

• Ice Crystals in Cirrus Clouds
  • High-Altitude Clouds: The phenomenon occurs in cirrus clouds, which are high-altitude clouds made up of ice crystals.
  • Crystal Shape: These ice crystals are typically hexagonal.
• Optical Processes
  • Inner 22-Degree Halo: When ice crystals are randomly oriented, light entering one face of the hexagonal crystal and exiting through another is refracted at a 22-degree angle, creating the inner halo.
  • Outer 46-Degree Halo: For the outer halo to form, the ice crystals need to be aligned horizontally with their flat faces parallel to the ground. This precise alignment causes additional refraction, resulting in the 46-degree halo.

Significance of the Double Sun Halo

• Insight into Atmospheric Conditions: Observing sun halos helps scientists understand the properties and behaviors of ice crystals in the atmosphere.
• Weather Forecasting: These observations can improve weather models and enhance our understanding of atmospheric optics.

Sun Halo

• A sun halo, also known as a 22-degree halo, is a ring of light that encircles the sun.
• This optical phenomenon is created by the refraction, reflection, and dispersion of light through ice crystals suspended in the atmosphere.
• Sun halos are fascinating natural occurrences that have been observed and documented throughout history.

Formation of Sun Halos

• Ice Crystals in the Atmosphere
  • Location: Sun halos form in cirrostratus clouds, which are high-altitude clouds composed predominantly of ice crystals.
  • Crystal Shape: The ice crystals responsible for sun halos are typically hexagonal in shape.
• Optical Processes Involved
  • Refraction: Light enters one side of the hexagonal ice crystal and exits through another, bending (refracting) at a specific angle.
  • Reflection: Some light may also reflect off the internal surfaces of the ice crystal, contributing to the halo effect.
  • Dispersion: The different wavelengths of light are separated, often causing a subtle spectrum of colors within the halo.

Types of Sun Halos

• 22-Degree Halo
  • Appearance: A bright ring at 22 degrees from the sun.
  • Colors: Often appears white but can show faint red on the inner edge and blue on the outer edge due to dispersion.
• 46-Degree Halo
  • Rarity: Less common than the 22-degree halo.
  • Appearance: A larger ring at 46 degrees from the sun, often less distinct.
• Other Variations
  • Parhelia (Sun Dogs): Bright spots on either side of the sun, often occurring in conjunction with a 22-degree halo.
  • Circumzenithal Arc: A brightly colored arc that forms directly overhead, similar to an upside-down rainbow.

Sources:

IndiaToday

PRACTICE QUESTION Q.  With reference to the Sun halo phenomenon, consider the following statements: A Sun halo is caused by the refraction and reflection of sunlight by ice crystals in the upper atmosphere. Sun halos are typically seen when the Sun is at a low angle in the sky, such as during sunrise or sunset. The most common type of Sun halo is a 22-degree halo, which appears as a ring around the Sun at an apparent radius of about 22 degrees. Which of the statements given above is/are correct? a) 1 only b) 1 and 2 only c) 1 and 3 only d) 1, 2, and 3 Answer: c)