How does the daily path of the Sun across the sky change with the seasons? Why does it change?

The Earth's axis is not upright but tilted at an angle of approximately 23.5 degrees from the vertical. This axial tilt is the reason why we experience seasons. As the Earth makes its yearly orbit around the Sun, the angle of tilt remains the same, but the hemisphere that is tilted towards the Sun changes. During half of the year, the Northern Hemisphere is tilted towards the Sun, enjoying warmer months, while the Southern Hemisphere experiences colder months. Conversely, when the Southern Hemisphere is tilted towards the Sun, it enjoys its summer as the Northern Hemisphere cools down.

Due to this tilt, sunlight strikes the Earth at different angles throughout the year. In June, the North Pole is inclined towards the Sun, which results in longer periods of daylight and a higher Sun path across the sky. In December, it is the opposite; the North Pole tilts away from the Sun, leading to shorter daylight hours and a lower Sun path. The axial tilt is essential in understanding the Sun's daily path across the sky, as it directly affects both the arc's length and height at different times of the year.

Seasonal changes are a direct consequence of the Earth's axial tilt and its orbit around the Sun. As the Earth orbits, various parts of the globe receive varying degrees of sunlight exposure, which translates into the different seasons we are all familiar with: spring, summer, autumn, and winter.

During summer in the Northern Hemisphere, the Sun's rays hit the Earth at a more direct angle, causing warmer temperatures and longer days. Conversely, in winter, the Sun's rays are more slanted, providing diffuse light and resulting in colder temperatures and shorter days. Spring and autumn serve as transitional periods where the temperatures and duration of daylight gradually shift. These seasonal changes affect not only the weather but also the ecosystem, influencing plant growth, animal behavior, and various human activities.

Solstices and equinoxes are key astronomical events that mark significant points in Earth's journey around the Sun. A solstice occurs when the Sun reaches its highest or lowest point in the sky at noon, resulting in the longest or shortest day. The summer solstice in the Northern Hemisphere happens around June 21 when the North Pole is tilted closest to the Sun, giving us the longest daylight period of the year. The winter solstice is around December 21, marking the shortest day when the North Pole is angled farthest from the Sun.

Equinoxes are the points in time when the Sun is directly above the equator, leading to nearly equal day and night. The vernal equinox around March 20 signals the start of spring in the Northern Hemisphere, whereas the autumnal equinox around September 22 indicates the beginning of fall. The occurrences of solstices and equinoxes are essential for understanding cultural rituals, historical calendars, and their effects on the Sun's daily path.

The Earth's orbit around the Sun is elliptical, with the Sun positioned off-center. This path takes approximately 365.25 days to complete, which is why every fourth year, a leap day is added to the calendar to maintain accuracy. The Earth's distance from the Sun changes slightly over the course of the year, but it's the axial tilt that is primarily responsible for seasonal changes, not our distance from the Sun.

During its orbit, the speed of the Earth varies due to the different distances, being faster when closer to the Sun and slower when farther away, a result of the gravitational laws described by Johannes Kepler. Understanding Earth's orbit helps to make sense of the seasonal weather patterns, timing of solstices and equinoxes, and the shifting pattern of the Sun's daily trajectory in the sky.