The Tilt of the Earth: Explaining the Sun’s Position at Noon

The Tilted Axis of the Earth

The primary reason why the sun is not in the south at noon is due to the Earth’s tilted axis. The Earth’s axis is tilted about 23.5 degrees relative to the plane of its orbit around the Sun. This tilt causes the seasons and the variations in the position of the sun in the sky throughout the year.

As the Earth rotates on its tilted axis, the angle of the sun’s rays changes. During the equinoxes, when the sun’s rays are perpendicular to the equator, the sun appears directly overhead at noon. During the solstices, however, the sun’s rays strike the Earth at a more oblique angle, causing the sun to appear either north or south of due east/west at noon, depending on the time of year.

The Earth’s elliptical orbit

In addition to the tilt of the Earth’s axis, the fact that the Earth orbits the Sun in an elliptical orbit also contributes to the Sun’s position not being due south at noon. As the Earth moves along its elliptical orbit, the distance between the Earth and the Sun changes slightly, affecting the apparent size and position of the Sun in the sky.
During the Northern Hemisphere summer, when the Earth is farther from the Sun, the Sun appears slightly smaller in the sky. Conversely, during the northern hemisphere’s winter, when the Earth is closer to the Sun, the Sun appears slightly larger. These slight changes in the apparent size and position of the Sun throughout the year also play a role in the Sun not being due south at noon.

The Sun’s Declination

The Sun’s declination, which is the angle between the Sun’s position and the celestial equator, is another key factor in the Sun’s position at noon. The Sun’s declination changes throughout the year as the Earth orbits the Sun and the Northern and Southern Hemispheres tilt toward and away from the Sun.

At the summer solstice, the Sun’s declination is at its northern maximum, causing the Sun to appear highest in the sky at noon. At the winter solstice, the sun’s declination is at its most southerly, causing the sun to appear lowest in the sky at noon. These changes in the Sun’s declination contribute to the Sun’s position not being due south at noon.

Geographic location and season

Finally, the position of the sun at noon is also affected by the geographic location of the observer and the time of year. For locations north or south of the equator, the position of the sun at noon will vary throughout the year. For example, at the North Pole, the Sun circles the sky at a constant angle above the horizon, and the Sun’s position at noon will change depending on the time of year.

Similarly, at locations closer to the equator, the sun’s position at noon will be closer to due south, but will still vary slightly throughout the year. Understanding these geographic and seasonal variations is critical to accurately predicting and understanding the sun’s position at noon in any given location.

FAQs

Why isn’t the sun due south at noon?

The sun is not due south at noon because the Earth’s axis is tilted at an angle of 23.5 degrees relative to the plane of its orbit around the sun. This tilt causes the sun’s apparent position in the sky to shift throughout the year, resulting in the sun being south of the observer at noon only on the equinoxes (around March 21 and September 21). At other times of the year, the sun will be either north or south of due south at noon, depending on the time of year.

How does the Earth’s tilt affect the sun’s position at noon?

The Earth’s tilt of 23.5 degrees causes the sun’s path across the sky to shift throughout the year. During the summer months in the Northern Hemisphere, the sun appears higher in the sky at noon, and its noon position is north of due south. During the winter months, the sun appears lower in the sky at noon, and its noon position is south of due south. This shift in the sun’s noon position is what causes it to not be due south at noon on most days.

What is the significance of the equinoxes in relation to the sun’s position at noon?

On the equinoxes (around March 21 and September 21), the sun is directly overhead at the equator, and its noon position is due south for observers in the Northern Hemisphere. This is because on the equinoxes, the sun’s path crosses directly over the equator, resulting in the sun being due south at noon for locations in the mid-latitudes. On all other days, the sun’s noon position is either north or south of due south, depending on the time of year and the observer’s latitude.

How does the sun’s noon position change throughout the year?

The sun’s noon position changes throughout the year due to the Earth’s tilt. In the Northern Hemisphere, the sun’s noon position is farthest north around the summer solstice (June 21) and farthest south around the winter solstice (December 21). On the equinoxes (March 21 and September 21), the sun is directly overhead at the equator, and its noon position is due south for observers in the mid-latitudes. In between these key dates, the sun’s noon position gradually shifts between these extremes.

What is the practical significance of the sun’s shifting noon position?

The shifting noon position of the sun has practical implications for things like solar energy generation, gardening, and navigation. Solar panels are often angled to optimize their exposure to the sun at noon, so understanding the sun’s noon position throughout the year can help maximize their efficiency. Gardeners also need to be aware of the sun’s noon position to plan where to plant sun-loving or shade-loving plants. And in navigation, the sun’s noon position is an important reference point for determining latitude and tracking one’s position on the Earth’s surface.