Why Does the Sun Move During the Day?

During the day, the sun appears to move across the sky in a path that forms an arc. This path is known as the sun path or the day arc and it is a consequence of the earth orbiting the sun and rotating about its axis. This path has many effects on the amount, intensity, and length of time that sunlight hits the surface. Different latitudes also come into play while determining the amount, intensity, and the duration that the sunlight hits the earth’s surface.

Tilting of the Earth Along the Axis

Basic geography teaches that the earth rotates on its axis for 24 hours at an angle of approximately 23.5 degrees to the plane of the orbit of the earth around the sun. With this knowledge, basic geometry can be used to determine the path of the sun.

Northern and Southern Hemisphere

In the Northern Hemisphere, during the winter solstice (November, December, and January), the sun follows a path from the southeast in the morning, at a low angle over the celestial meridian in the south, and finally sets in the southeast. The sun path is on the equator-facing side of the house throughout the day. For the people wanting to capture and harness solar energy, they should place their devices facing this side. In contrast, the sun pat in the Southern Hemisphere during the winter solstice rises in the northeast and eventually goes down in the northwest. Solar energy capturing devices would be most effective if they are trained north.

Summer Solstice

During the summer solstice (May, June, July), the direction of the sun reverses. In the Northern Hemisphere, the sun rises in the northeast and eventually sets in the northwest. In the Southern Hemisphere, the sun path originates from the southeast during sunrise and ends in the southwest.

Spring Equinox and Fall Equinox

The equinoxes are different. Equinox refers to the time or date of the year where the sun moves across the equator and day and night are of the same lengths. This phenomenon occurs twice a year on March 20/21 and September 22/23. In the Northern Hemisphere, during the equinoxes, the sun peaks in the southern half while the sun peaks in the northern half in the Southern Hemisphere. To put it in simpler terms, the sun will seem to move from the left to right while standing in the Northern Hemisphere and facing the equator. The reverse is true while facing the equator in the Southern Hemisphere. The position of the sun in the stars may also affect the movement.

Effects and Importance of Sun Movement

Knowledge of the sun path is vital to many things including decision-making for things like effective usage of solar trackers, shading for the summer, landscaping, and other uses. Methods, techniques, and equipment are available for this purpose.

For example, this information is critical to those who design houses with windows for capturing solar energy. This data will help them to build and make designs that have optimally placed windows and overhangs to block unwanted heat while seasons change at different times of the year in that particular region.