Answer · confidence: partial
How much of the glow in the sky near the horizon at dusk comes from light that has bounced more than once before reaching the eye?
The records show that polarization studies found multiple scattering contributes about 50% of the twilight background even at sunset, in the blue part of the spectrum 4. A 2013 study reports that near the horizon at twilight, multiply scattered light dominates the sky, with the singly scattered fraction below 20% 5. Taken together, these suggest that most of the near-horizon glow may come from multiple scattering, but the two figures come from different contexts, and the 50% figure describes the twilight background generally rather than the horizon specifically 45. The records do not give one precise percentage for the near-horizon glow at dusk. The newest relevant fact is from 2018, about eight years before October 2026, and it concerns Titan rather than Earth 10.
Checked 2026-10-19. Only documented and supported facts are used.
Dig deeper on this questionSources
[1] documented
The ratio of primary scattering to total scattering is a measure of multiple scattering, calculated as 100 minus the percentage of multiple scattering relative to total scattering.
"This quotient is a measure of multiple scattering because of the relation: Total Scattering (TS) is equal to Primary Scattering (PS) plus Multiple Scattering (MS), i.e. PS/TS = 100 - MS/TS (%)."The ratio of primary scattering to total scattering of sky radiance (1974)
[2] documented
Multiple scattering is related to the optical thickness, which is equivalent to extinction.
"The present work shows in which way multiple scattering is related to the optical thickness, i.e. the extinction."The ratio of primary scattering to total scattering of sky radiance (1974)
[3] documented
The ratio of primary scattering to total scattering is a measure of multiple scattering, calculated as 100 minus the percentage of multiple scattering relative to total scattering.
"This quotient is a measure of multiple scattering because of the relation: Total Scattering (TS) is equal to Primary Scattering (PS) plus Multiple Scattering (MS), i.e. PS/TS = 100 - MS/TS (%)."The ratio of primary scattering to total scattering of sky radiance (1974)
[4] supported
Polarization studies found that multiple scattering contributes about 50% of the twilight background even at sunset, in the blue part of the spectrum.
"Polarization study [19, 20] had shown that multiple scattering contribution is high even at sunset, reaching 50% in blue part of spectrum."Detection of Molecular Scattering Field by Polarization Analysis of Sky Background During the Transitive Twilight and Temperature Measurements near the Stratopause
[5] documented
Near the horizon at twilight, multiply scattered light dominates the sky, with the singly scattered fraction (ISS/I) below 20%.
"the twilight sky near the horizon, where multiply scattered light dominates (ISS /I less than 20%), tends to be blue."Physical Explanation of Tropospheric Aerosol Effects on Twilight Sky Color Based on Photographic Observations and Radiative Transfer Simulations (2013)
[6] supported
The contribution of multiple scattering to the twilight background was noticed in the 20th century but was underestimated for a long time.
"Necessity of its account was noticed in XX century [18] but its value was underestimated for a long time."Detection of Molecular Scattering Field by Polarization Analysis of Sky Background During the Transitive Twilight and Temperature Measurements near the Stratopause
[7] documented
As tropospheric aerosol optical depth increases, reddish singly scattered light is strongly attenuated by dense lower-tropospheric aerosols, so bluish multiply scattered light comes to dominate.
"With increasing tropospheric AOD, reddish singly scattered light is strongly attenuated by dense aerosols in the lower troposphere, but blue multiply scattered light dominates."Physical Explanation of Tropospheric Aerosol Effects on Twilight Sky Color Based on Photographic Observations and Radiative Transfer Simulations (2013)
[8] supported
The document attributes a secondary red/green maximum in volcanic twilights, seen at sun depressions greater than 6°, to multiple scattering rather than mesospheric dust. It does not give a quantitative share of the glow from multiply scattered light.
"This seems to have been caused by multiple scattering and not by mesospheric dust."Twilights and Stratospheric Dust Before and After the Agung Eruption (1969)
[9] documented
The paper reports that multiple scattering has relatively minor influence on recovering stratospheric dust properties from twilight sky measurements, provided the mean altitude of the haze layer is between 10 and 30 km. The document gives no specific percentage for the share of multiply scattered light.
"The presence of haze in the lower troposphere and the occurrence of multiple scattering both have relatively minor influences on the recovery of the stratospheric dust properties, provided that 10< \(\overline h \) <30 km."Radiance and color of the sky at twilight: Perturbations caused by stratospheric haze (1980)
[10] documented
Near-horizon illumination on Titan is strongest when the Sun is highest in the sky, which the authors attribute to the intensity of multiple scattering.
"The total near-horizon illumination maximizes when the Sun is highest in the sky owing to the intensity of multiple scattering."Titan’s Twilight and Sunset Solar Illumination (2018)
[11] supported
Light reaching the surface from low in the sky near Titan's horizon is diffusely scattered light.
"Shadows below the lander should receive illumination from diffusely scattered light low in the sky near Titan's horizon."Titan’s Twilight and Sunset Solar Illumination (2018)
[12] supported
In the twilight solar zenith angle range of 88–94°, single scattering plays a dominant role in the sky brightness, while the relative contribution of multiple scattering depends on the aerosol loading.
"showsthatsinglescatteringplaysadominantroleintheSZA"Nabro volcano aerosol in the stratosphere over Georgia, South Caucasus from ground-based spectrometry of twilight sky brightness (2013)