Every morning, as twilight begins to glow, the Sun rises from the east, on its daily path towards the western horizon, leading the day into the night. The path of the Sun traverses the sky propelled by the eastward rotation of the Earth, moving it along the horizon from east to west.
But exactly where in the east or west the Sun will rise or set is decided by the Earth’s tilt and its position within its ecliptic orbit around the Sun. It may rise northeasterly or southeasterly and, for the same reason, set northwesterly or southwesterly.
Only twice a year during the spring and fall equinox will the Sun rise and set precisely on the cardinal direction of “due east” and “due west.”
So, let’s explore the movements of the Earth and Sun to better understand how their interaction creates this wonderful experience each and every day.
Our Sun Centered Solar System
On any given day or night, the movements of celestial objects in the sky could make skywatchers perceive that everything within the heavens revolves around the Earth. It was only a few chapters back in our human history that this was the storyline!
Thankfully, this book is a work in progress. Due to the curiosity and intellect of astronomers such as Nicolaus Copernicus and Galileo, by the end of the 18th century, most of the world overwhelmingly accepted the Copernican understanding of a heliocentric, sun-centered system as we know it today.
Understanding Earth’s Rotation,
Orbit and Tilt
Like the other seven planets in our system, Earth orbits the center of our solar system, the Sun. While on its ecliptic orbit, much like a gyroscope top spinning across the floor, the Earth spins on an imaginary line called the axis of rotation.
This axis stretches from the North Pole to the South Pole, and Earth rotates eastward around it. It’s this rotation that causes the Sun to appear to rise in the east and set in the west for most locations on our planet.
The axial tilt is an imaginary line running between poles at an angle of approximately 23.44˚. As the Earth makes its way around its ecliptic orbit of the Sun, the tilt affects where the position of the Sun will be seen in the sky and where precisely it will rise or set within the east and west depending on the Earth’s position within its orbit of the Sun.
The celestial equator is an imaginary extension of Earth’s equator into space. It sits on the same plane as the equator and divides the imaginary celestial sphere into the northern and southern hemispheres. Since Earth’s axis is tilted relative to its orbit, the celestial equator is also tilted with respect to the ecliptic – the path the Sun seems to take across the sky, which affects the Sun’s apparent path during the day.
The axial tilt and where the Earth is positioned within its ecliptic orbit, affects which hemisphere is more directly facing the Sun, impacting the length of day and night, which season that hemisphere will experience. The Solstice and Equinox are points within our yearly orbit.
The Solstice and Equinox
Fall and Spring Equinox
Both the solstice and equinox mark a change of season and length of day. The equinox signals a point within Earth’s orbit when the Sun is directly above the celestial equator. This marks a time when the Sun will rise in exact east and set in exact west. Day and night are of equal length of time, and it’s the beginning of a new season as the Sun crosses from one hemisphere into the other. Twice within its solar orbit, the Earth reaches an equinox. Once at the beginning of Autumn, the Fall Equinox is about September 23, and once at the beginning of Spring, the Vernal Equinox is about March 21.
Summer and Winter Solstice
The solstice indicates the Sun is at its furthest point north or south from the Equator. In the northern hemisphere, the Summer Solstice (June Solstice, June (20 or 21)) marks the beginning of Summer when the Sun is positioned highest in the sky, marking the year’s longest day.
The Winter Solstice (December Solstice, December (21 or 22)) is the beginning of winter and marks the shortest day of the year. The southern hemisphere is experiencing the exact opposite season as the northern hemisphere. The longest day of the year in the northern hemisphere is the shortest day of the year in the southern hemisphere, and so forth.
During the solstice, in the polar regions of the Arctic and Antarctic circles, Polar Night and Day occur, where it remains dark or light, depending on which hemisphere, for more than 24 hours. This experience only happens within the polar circles.
Observing Sunrise
and Sunset
The solar path angle at which the sun rises and sets is not constant; it is shaped by your geographical location and the time of year. At the equinoxes, the sun rises due east and sets due west no matter where your location is on Earth.
As the seasons progress towards the solstice, the sunrise and sunset points move northward or southward on the horizon. Your latitude plays a significant role; the closer you are to the equator, the less variation you will observe in the sunrise and sunset angles and the less length of time a sunrise or sunset will last before it gets dark.
Historical Perspectives
From ancient cultures to modern times, predictable patterns of sunrise and sunset have been critical in developing navigational and time keeping tools such as calendars.
One well known example is the stone circle of Stonehenge, the prehistoric site in England which aligns with the solstice sunsets, demonstrating the significance it had for the Neolithic people for both timekeeping and symbolic rituals.
Navigational Relevance
Navigating by celestial bodies, particularly the Sun, has been a reliable method for travelers and seafarers throughout history. Understanding the Sun’s path was a crucial component. By observing the direction of sunrise and sunset, they inferred latitude which helped in plotting their course.
You can use the apparent movement of the Sun and it’s position to determine direction with a basic understanding of its daily movement. At solar noon, when the sun reaches its highest point in the sky, it will be due south in the northern hemisphere and due north in the southern hemisphere. This method assumes an observer at a moderate latitude; deviations occur based on geographic location and the Earth’s tilt.
To improve accuracy, you can mark the sunrise and the point of sunset with physical markers to create an East-West line. Stand with the sunrise to your left and sunset to your right—now you’re facing true north.
Conclusion
Due to the nature of our world and the cosmos today, the Sun will always rise from the east and set in the west from dawn to dusk. All the nuances of geographic position and the seasons will have an impact on where in the east and west the Sun rises and sets along the horizon. From the polar regions to the equatorial belt, understanding these seasonal shifts can instill a higher appreciation of these natural skyscapes of color that decorate your specific corner of the world throughout the year.
