Abstract
Even though the longest day occurs on the June solstice everywhere in the Northern Hemisphere, this is NOT the day of earliest sunrise and latest sunset. Similarly, the shortest day at the December solstice in not the day of latest sunrise and earliest sunset. An analysis combines the vertical change of the position of the Sun due to the tilt of Earth’s axis with the horizontal change which depends on the two factors of an elliptical orbit and the axial tilt. The result is an analemma which shows the position of the noon Sun in the sky. This position is changed into a time at the meridian before or after noon, and this is referred to as the equation of time. Next, a way of determining the time between a rising Sun and its passage across the meridian (equivalent to the meridian to the setting Sun) is shown for a particular latitude. This is then applied to calculate how many days before or after the solstices does the earliest and latest sunrise as well as the latest and earliest sunset occur. These figures are derived for 60 cities in the USA. The selection was initially based on the most populous urban areas but was extended to ensure that each of the 50 states has a representative city.
Highlights
The June solstice is the longest day of the year in the USA and the December solstice is the shortest
Calculations in this paper show that: The earliest sunrise happens before the June solstice and the latest sunset after; The latest sunrise happens after the December solstice and the earliest sunset before; The effect at the December solstice is more pronounced than for the June one and The number of days departure for earliest/latest sunrise/sunset from the longest and shortest days is latitudinally dependent and increases towards the equator
The union of the elevation for a specific locality (Figure 3) and deviation from the meridian (Figure 8) for the Sun results in the construction of an analemma, which is in the shape of a figure eight
Summary
The June solstice is the longest day of the year in the USA and the December solstice is the shortest. Calculations in this paper show that: The earliest sunrise happens before the June solstice and the latest sunset after; The latest sunrise happens after the December solstice and the earliest sunset before; The effect at the December solstice is more pronounced than for the June one and The number of days departure for earliest/latest sunrise/sunset from the longest and shortest days is latitudinally dependent and increases towards the equator. Calculations in this paper are based on Central Standard Time of -6 hours difference, with Chicago being the representative locality.
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