The annual march of solar declination refers to the movement of the sun’s position in relation to the Earth’s equator throughout the year. This movement is caused by the tilt of the Earth’s axis, which is approximately 23.5 degrees. As a result of this tilt, the sun appears to migrate between the Tropic of Cancer (23.5 degrees north of the equator) and the Tropic of Capricorn (23.5 degrees south of the equator) over the course of the year.
The summer solstice, which occurs on June 21 in the Northern Hemisphere, marks the point at which the solar declination reaches its farthest poleward migration for that hemisphere. This means that the sun is directly overhead at the Tropic of Cancer on this day, making it the longest day of the year in terms of daylight hours. Conversely, in the Southern Hemisphere, June 21 marks the winter solstice, where the solar declination reaches its farthest poleward migration towards the Tropic of Capricorn. This makes it the shortest day of the year in terms of daylight hours.
As the year progresses, the solar declination gradually migrates towards the opposite tropic. In the Northern Hemisphere, the sun appears to move southward from the Tropic of Cancer towards the equator. This results in shorter days and cooler temperatures. In the Southern Hemisphere, the sun appears to move northward from the Tropic of Capricorn towards the equator, leading to longer days and warmer temperatures.
The migration of solar declination has significant implications for the seasons and climate patterns experienced in different parts of the world. For example, regions near the equator experience relatively stable and consistent weather patterns throughout the year, as the sun is always relatively high in the sky and the length of day and night remains fairly constant. On the other hand, regions closer to the poles experience more pronounced seasonal variations, with longer days in the summer and shorter days in the winter.
These changes in solar declination also have important effects on the amount and intensity of solar radiation received at different latitudes. When the sun is directly overhead at a particular latitude, the amount of solar energy received is maximized, leading to warmer temperatures. As the sun’s angle decreases, the same amount of solar energy is spread over a larger area, resulting in cooler temperatures.
The annual march of solar declination refers to the movement of the sun’s position between the Tropic of Cancer and the Tropic of Capricorn throughout the year. This movement is caused by the Earth’s axial tilt and has significant effects on the seasons, climate patterns, and amount of solar radiation received at different latitudes.