The Chromaticity of Total Lunar Eclipses and the Modified Danjon Scale as an Indirect Measure of Stratospheric Aerosols

Falcon N, Falcon O and Ortega A

Published on: 2023-01-28

Abstract

During Total Lunar Eclipses, the lunar disk penetrates the Earth's umbra cone and shows an opaque coloration due to the deviation of the sun's rays when passing through the Earth's atmosphere. This shaded Moon is used to assess global stratospheric transparency, even in paleoclimatological periods. The brightness and coloration of the shadowed Moon is rated via the Danjon scale, but this is a poorly defined qualitative scale and cannot be related to the chromaticity and RGB color space of digital images. The chromatic evaluation of the total lunar eclipses in the period 2000-2022 is presented through the analysis of digital photographs. The results allow us to define a modified Danjon scale, through the normalized module of the color vector in the RG subspace of the digital color. This FD number or Danjon factor constitutes an effective and unambiguous measure of the luminosity and chromaticity in Total Lunar Eclipses, and can be correlated with the emissions of aerosols volcanic origin, allowing delimiting their relative concentration in the stratosphere.

Keywords

Danjon scale; Total Lunar eclipse; stratospheric aerosols; RGB digital colors

Introduction

During the Total Eclipses of the Moon, the lunar disk penetrates the Earth's umbra cone and does not completely darken, but instead shows an opaque coloration in the visible region of the electromagnetic spectrum. This coloration and brightness of the Moon varies in each particular eclipse from an ocher-yellow to a dark red. This coloration is due to deviation of the solar rays when crossing the terrestrial atmosphere, and projecting on the moon.

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