Editing Sunset (section)

==Occurrence==
{{See also|Analemma}}
[[File:Twilight subcategories.svg|thumb|Stages of the twilight period]]
The time of sunset varies throughout the year and is determined by the viewer's position on Earth, specified by [[latitude and longitude]], [[altitude]], and [[time zone]]. Small daily changes and noticeable semi-annual changes in the timing of sunsets are driven by the [[Axial tilt|axial tilt of the Earth]], daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun, and the Earth and Moon's paired revolutions around each other. During winter and spring, the days get longer and sunsets occur later every day until the day of the latest sunset, which occurs after the summer solstice. In the [[Northern Hemisphere]], the latest sunset occurs late in June or in early July, but not on the summer solstice of June 21. This date depends on the viewer's latitude (connected with the Earth's slower movement around the [[aphelion]] around July 4). Likewise, the earliest sunset does not occur on the winter solstice, but rather about two weeks earlier, again depending on the viewer's latitude. In the Northern Hemisphere, it occurs in early December or late November (influenced by the Earth's faster movement near its [[perihelion]], which occurs around January 3).{{citation needed|date=October 2021}}

Likewise, the same phenomenon exists in the [[Southern Hemisphere]], but with the respective dates reversed, with the earliest sunsets occurring some time before June 21 in winter, and the latest sunsets occurring some time after December 21 in summer, again depending on one's southern latitude. For a few weeks surrounding both solstices, both sunrise and sunset get slightly later each day. Even on the equator, sunrise and sunset shift several minutes back and forth through the year, along with solar noon. These effects are plotted by an [[analemma]].<ref>[http://www.starrynight.com/sntimes/2007/01/ Starry Night Times – January 2007] (explains why Sun appears to cross slow before early January)</ref><ref>[http://www.analemma.com/Pages/framesPage.html The analemma] {{Webarchive|url=https://web.archive.org/web/20061018175524/http://www.analemma.com/Pages/framesPage.html |date=2006-10-18 }}, elliptical orbit effect. 'July 3rd to October 2nd the sun continues to drift to the west until it reaches its maximum "offset" in the west. Then from October 2 until January 21, the sun drifts back toward the east'</ref>

Neglecting atmospheric refraction and the Sun's non-zero size, whenever and wherever sunset occurs, it is always in the northwest quadrant from the [[March equinox]] to the [[September equinox]], and in the southwest quadrant from the September equinox to the March equinox. Sunsets occur almost exactly due west on the equinoxes for all viewers on Earth. Exact calculations of the [[azimuth]]s of sunset on other dates are complex, but they can be estimated with reasonable accuracy by using the analemma.{{citation needed|date=October 2021}}

As sunrise and sunset are calculated from the leading and trailing edges of the Sun, respectively, and not the center, the duration of a [[daytime]] is slightly longer than nighttime (by about 10 minutes, as seen from temperate latitudes). Further, because the light from the Sun is refracted as it passes through the Earth's atmosphere, the Sun is still visible after it is geometrically below the horizon. Refraction also affects the apparent shape of the Sun when it is very close to the horizon. It makes things appear higher in the sky than they really are. Light from the bottom edge of the Sun's disk is refracted more than light from the top, since refraction increases as the angle of elevation decreases. This raises the apparent position of the bottom edge more than the top, reducing the apparent height of the solar disk. Its width is unaltered, so the disk appears wider than it is high. (In reality, the Sun is almost exactly spherical.) The Sun also appears larger on the horizon, an optical illusion, similar to the [[moon illusion]].{{citation needed|date=October 2021}}

Locations within the [[Arctic]] and [[Antarctic Circle|Antarctic Circles]] experience periods where the Sun does not rise or set for 24 hours or more, known as [[Midnight sun|polar day]] and [[polar night]]. These phenomena occur due to [[Axial tilt|Earth’s axial tilt]], causing continuous sunlight or darkness at certain times of the year.<ref>{{Cite web |title=Equinox |url=https://education.nationalgeographic.org/resource/equinox/ |access-date=2024-11-26 |website=education.nationalgeographic.org |language=en}}</ref>