# What is the optical depth of the sun?

## What is the optical depth of the sun?

approximately 1011
The total optical depth of the whole Sun is approximately 1011. Aside from the corona and chromosphere, only a very thin surface of the Sun, the photosphere, is visible (Artymowicz, 2010).

## What is the optical depth of the solar atmosphere?

2/3
Hence for the Sun, where the majority of photons are emitted in the visible wavelength, the photosphere is often defined as the layer where light emitted at 5000 Å (green) has an optical depth of 2/3, ).

## How is optical depth calculated?

dF = -ρa kabs F dx. where ρa is the mass density of a (units kg a / m3 air) and kabs is the absorption coefficient (m2 kg-1). F∞ θ is the “solar zenith angle”. Remember τ here is defined as the vertical optical depth.

## What does an optical depth τ of one mean?

physical distance (vertical or horizontal), we rescale to a dimensionless coordinate, where optical depth = 1 means that only e-1 = 0.368 of the energy is passed without being extincted (absorbed or scattered) in passing through one unit of optical depth. τ v. (z)= ρ

## What happens to photons at optical depth 2 / 3?

This means that each photon emitted at the photosphere suffers an average of less than one scattering before it reaches the observer. At the temperature at optical depth 2/3, the energy emitted by the star (the original derivation is for the Sun) matches the observed total energy emitted.

## How is spectral absorbance related to optical depth?

Tλ is the spectral transmittance in wavelength of that material. Spectral absorbance is related to spectral optical depth by: Aλ is the spectral absorbance in wavelength. Optical depth measures the attenuation of the transmitted radiant power in a material.

## How is the optical depth of the atmosphere measured?

The optical depth of the atmosphere can be divided into several components, ascribed to Rayleigh scattering, aerosols, and gaseous absorption. The optical depth of the atmosphere can be measured with a sun photometer. The optical depth with respect to the height within the atmosphere is given by.

## What causes the attenuation of the optical depth?

Attenuation can be caused by absorption, but also reflection, scattering, and other physical processes. Optical depth of a material is approximately equal to its attenuation when both the absorbance is much less than 1 and the emittance of that material (not to be confused with radiant exitance or emissivity) is much less than the optical depth: