Sunrise

[1] Also, unlike most other solar measurements, sunrise occurs when the Sun's upper limb, rather than its center, appears to cross the horizon.

[1] Accounting for atmospheric refraction and measuring from the leading edge slightly increases the average duration of day relative to night.

This symmetry becomes clear if the hemispheric relation in to the sunrise equation is applied to the x- and y-components of the solar vector presented in Ref.

[9] At sunrise and sunset, when the path through the atmosphere is longer, the blue and green components are removed almost completely, leaving the longer-wavelength orange and red hues seen at those times.

The remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange.

[9][10][12][15] Ash from volcanic eruptions, trapped within the troposphere, tends to mute sunset and sunrise colors, while volcanic ejecta that is instead lofted into the stratosphere (as thin clouds of tiny sulfuric acid droplets), can yield beautiful post-sunset colors called afterglows and pre-sunrise glows.

A number of eruptions, including those of Mount Pinatubo in 1991 and Krakatoa in 1883, have produced sufficiently high stratospheric sulfuric acid clouds to yield remarkable sunset afterglows (and pre-sunrise glows) around the world.

The high altitude clouds serve to reflect strongly reddened sunlight still striking the stratosphere after sunset, down to the surface.