Sunrise and sunset times for Firenze in 2023. Shortest day and longest day.

Twilight is the gradual passage of illumination that joins the deep night with the day (morning twilight) and the day with the deep night (evening twilight), where by day we mean the temporal interval between sunrise and sunset, i.e. until the first and last ray of the Sun arrives directly on the Earth. Late night is that period of total shade, in which sunlight no longer has any contribution. During twilight, the Earth still receives an indirect contribution from solar illumination, through the scattering and reflection of light by the atmosphere.
Twilight is conventionally measured at sea level and at the celestial equator, as an angular variation of the Earth's rotation, for a total of 18°, and is divided into three types (astronomical, nautical, civil), each of 6°.
The morning astronomical twilight includes the period between the end of the astronomical night when the center of the Sun reaches 108° of the zenith distance (-18° from the horizon) and the beginning of the nautical twilight (102° of zenith distance, -12° from the horizon). When the Sun is at -18° from the horizon, its contribution to illuminating the sky is almost zero. The evening astronomical twilight is also defined in a specular way.
Morning nautical twilight includes the period between the end of astronomical twilight and the beginning of civil twilight (96° of zenithal distance°, -6° from the horizon). During this time it is possible to distinguish the line of the marine horizon and the main stars at the same time. In these conditions, using nautical measuring instruments, such as the sextant, it is possible to establish one's geographical location and trace the navigation routes (hence the name). The evening nautical twilight is also defined in a specular way.
Morning civil twilight includes the period between the instant in which the centre of the Sun reaches the zenithal distance of 96° (-6° from the horizon) and its first rise. In the brightest part of this range it is still possible to distinguish the colors of objects.
The aurora is the appearance of light just before sunrise. It constitutes the last phase of the morning twilight or dawn. While in the early stages of twilight the luminosity is mainly due to sunlight reflected from the upper layers of the atmosphere, during the aurora the colored light refracted from the lower layers predominates.