Sky radiance during a total solar eclipse: a theoretical model

Area of Science:

• Atmospheric physics
• Radiative transfer theory
• Solar eclipse studies

Background:

• Total solar eclipses offer unique opportunities to study atmospheric light scattering.
• Understanding sky radiance during an eclipse is key to interpreting observational data.

Purpose of the Study:

• To develop and present an approximate radiative transfer model for estimating sky radiance during a total solar eclipse.
• To validate the model against observed features of the eclipsed sky.

Main Methods:

• The model considers sunlight diffusion into the umbra via first- and second-order scattering.
• It focuses on predicting zenith radiance and horizon reddening.

Main Results:

• The model successfully predicts horizon reddening and a significant drop in zenith radiance (approx. 4 orders of magnitude).
• Calculated zenith radiance at blue wavelengths was ~20% lower than observed in the 1973 African eclipse.
• The model confirms the zenith exhibits the highest blue-red ratio and lowest brightness during totality.

Conclusions:

• The approximate radiative transfer model provides valuable insights into the optical phenomena of a total solar eclipse.
• The model's predictions align with key observational characteristics, validating its utility.
• Further refinement could improve the quantitative accuracy of radiance estimations.