My Dejected Posture is Because of This: What is Axial Tilt?
- Mar 20
- 12 min read
Updated: Mar 21
We have an Earth that rotates tirelessly, both around its own axis and around the Sun. Okay, it rotates, but these rotations have their own characteristics, and we have questions about them. For example, what is axial tilt? Imagine the Earth as a head without a body. Now imagine its nose is slightly lower or higher, or to the right or left. The position of that imaginary nose will answer the question of what axial tilt is. But how does it occur, what are the consequences of axial tilt, what happens if it increases or decreases, what would happen if there were no axial tilt? As the Galaxy Explorer, I will answer these questions for you.
Contents
What is axial tilt?
Let's start by asking what axial tilt means. Axial tilt, or inclination, is the name given to the angle between a planet's rotational axis and its orbital axis. To make it easier to understand, let me put it this way: if you draw an imaginary plus (+) sign on Earth, the north and south poles will not fall perpendicularly from that sign; one pole will be on the right and the other on the left.
How does axial tilt occur?
We don't know exactly how the axial tilt of planets formed. However, thanks to the Big Impact hypothesis, we have an idea: a massive object collided with Earth in its early stages. If you've read my Solar System blog, I explained how the inner or terrestrial planets formed. Neptune and Jupiter, pushed into the outer orbit of the Solar System due to the orbital resonance of Jupiter and Saturn, and Saturn's displacement from the Sun, caused a Late Heavy Bombardment in the inner orbit of the system. During this bombardment, a celestial body about the size of Mars collided with Earth, shifting Earth's vertical axial tilt. This collision even created the Moon, which reflects sunlight at night, illuminating our evenings.
What are the consequences of axial tilt?
Let's explain the consequences of axial tilt using Earth as an example. It's easier to illustrate this point by using our own planet as a model. Here's an example of Earth's axial tilt and its consequences:
Seasons: The axial tilt causes different regions of the Earth to receive varying amounts of sunlight throughout the year, leading to changes in the seasons.
Temperature variations: The axial tilt causes extreme temperature differences between the poles and the equator, with the poles receiving approximately 40% of the energy the equator receives.
Midnight Sun: At high latitudes, the sun does not set on some summer nights, creating a phenomenon known as the Midnight Sun.
Ice accumulation: Axial tilt, at high latitudes, contributes to the formation of ice sheets due to high albedo (a high albedo value indicates low heat retention potential of the ground).
Axial precession: The slow, cyclical wobble in the Earth's rotational axis causes the direction of the axial tilt to change slowly over time, affecting seasonal contrasts and climate patterns.
Milankovitch cycles: Axial tilt is part of the Milankovitch cycles, which have influenced Earth's climate in the past and continue to shape climate models.
Sea Level Changes: Due to the axial tilt, the melting of polar ice can contribute to changes in sea levels that have effects on coastal regions and human populations.
Geological Processes: Changes in climate and ice distribution caused by axial tilt can affect geological processes such as erosion, sedimentation, and crustal movement.
So, the axial tilt and its consequences generally affect the planet's energy intake and seasons. Now, in our next section, let's examine what would happen if there were no axial tilt.
What would happen if there were no axial tilt?
If the planets had no axial tilt, there would be no seasonal changes. Each latitude zone would have its own season throughout the year, with some minor variations depending on the planet's distance from the sun in its normal orbit. Cold regions of the planet would become even colder, and deserts and hot regions would become even hotter, making them uninhabitable. Regions with high rainfall would either be covered in forests or constantly subjected to topsoil erosion, making agriculture impossible in most areas.
How is axial tilt measured?
A planet's axial tilt is calculated as the angle between its axis of rotation and its orbital axis, or equivalently, the angle between its equatorial plane and its orbital plane. For Earth, this angle is known as the obliquity of the ecliptic and is denoted by the Greek letter “ε”. The exact angular value of the obliquity is found by observing planetary movements over many years. As the accuracy of observations increases, astronomers produce new fundamental ephemerides (the natural positions of celestial bodies), and various astronomical values, including obliquity, can be derived from these ephemerides.
How is axial tilt measured?
The equipment used to calculate axial tilt is an accelerometer. An accelerometer is a sensor that measures acceleration, including acceleration due to gravity. An accelerometer can determine the orientation of an object relative to the direction of gravity by measuring the direction and magnitude of the gravitational force. This can be used to calculate the angle between the object's axis of rotation and its orbital axis, i.e., the axial tilt. Accelerometers can be single-axis or dual-axis depending on the number of sensing elements they have. They can also be solid pendulum tilt sensors or liquid pendulum tilt sensors, depending on their design.
The Formation of Seasons and Axial Tilt
The formation of seasons is directly related to a planet's axial tilt. For example, Earth has four seasons because its rotational axis is tilted at an angle of approximately 23.5 degrees relative to its orbital plane. This tilt causes different regions to receive varying amounts of sunlight throughout the year, resulting in the formation of seasons.
Summer occurs when one hemisphere is more tilted towards the Sun, and winter occurs when it is further away from the Sun. If the Earth's axis were not tilted, there would be no seasonal changes, and every latitude zone would have the same season throughout the year with minimal variations depending on the planet's distance from the Sun in its normal orbit.
Are Annual Movement and Axial Tilt the Same Thing?
Annual motion and axial tilt are not the same thing: Annual motion is a planet's orbit around its star ; axial tilt is the angle between a planet's rotational axis and its orbital axis.
Axial tilt does not change significantly over an orbital period; we observe the repeating cycle of a planet's orbit around its star during its annual motion, and we can easily study the planet's movement.
What You Need to Know About Earth's Axial Tilt
Now let's learn about the axial tilt of the Earth, our common home, who discovered it, and what its consequences are.
What is the Earth's axial tilt in degrees?
The Earth's axial tilt is 23.44 degrees. This tilt causes summer in the northern hemisphere and winter in the southern hemisphere when the North Pole is pointing towards the sun. When the South Pole is pointing towards the sun, the situation reverses after six months.
Who discovered the Earth's axial tilt?
Technically, the first person to calculate the axial tilt was Ibn al-Shatir in the 14th century, but the first accurate and modern observations of the axial tilt were made by the Danish astronomer Tycho Brahe in 1584. However, there is evidence before that. It is believed that the Earth's axial tilt was calculated in China around 1100 BC. According to the Greek philosopher Pliny, Anaximander measured the Earth's tilt in 570 BC. Gassendi also wrote that the Greek Thales measured the axial tilt around the same time. It is accepted that the axial tilt was measured quite accurately by Pytheas around 300 BC. According to Ptolemy, the person who calculated the Earth's axial tilt as 23 degrees 51 minutes in 240 BC and found the closest value to the truth was the Greek mathematician Eratosthenes.
How was the Earth's axial tilt measured in the past?
Phoenician sailors, while navigating south of Africa around 600 BC, observed that the sun followed a path tilted northward during the day. They knew that in the Northern Hemisphere (Mediterranean region), the sun set following a path tilted southward. Greek philosophers declared this observation to prove the Earth's spherical shape. Furthermore, the existence of seasons, the equal length of day and night twice a year, the sun's high position in summer and its lower position in winter, and the fact that the sun illuminated the bottom of water wells in Aswan, Egypt, at noon on June 21st, all indicated that the Earth's axis was tilted.
The Greek mathematician Eratosthenes measured the length of a stick and its shadow at noon on June 21, 240 BC, in Alexandria, Egypt. He also knew that at the same time and date, the sun's rays illuminated the bottom of a well in Aswan. He calculated the circumference of the Earth using the angle between the stick and the sun's rays and the distance between two cities. To calculate the Earth's axial tilt , Eratosthenes measured and recorded the lengths of the stick and its shadow, which he had placed vertically on June 21st at 12 o'clock . He measured the lengths of the stick and its shadow again on December 22nd. From the length of the stick and its shadow, he calculated the angle between the sun's rays and the stick. By subtracting the angle he found on June 21st from the angle he found on December 22nd and dividing the remainder by 2, Eratosthenes found the Earth's axial tilt to be 23 degrees 51 minutes. The Iranian Abu M. Khojandi calculated the axial tilt as 23 degrees 32 minutes using this method in 994.
How did the Earth's axial tilt develop?
When Earth was still a baby planet, it was struck by a celestial body roughly the size of Mars, shifting its axis. If you're wondering where this body came from, we blame Jupiter and Saturn. The orbital resonance of Jupiter and Saturn pushed Neptune and set in motion a series of celestial bodies of varying sizes surrounding the outer reaches of the system. This resulted in a Late Heavy Bombardment in the inner orbit of the Solar System. The collisions during this bombardment were so powerful that the Moon is thought to have formed from the debris scattered by the collision between Earth and that massive object. It's also believed that the impacting body brought water to Earth, but that it wasn't the only primary source.
Special Dates Regarding the Earth's Axial Tilt
The Earth's orbital position during periods of its specific axial tilt.
The dates when the Earth's axial tilt is particularly significant are: March 21, June 21, September 23, and December 21. Now let me explain why we consider these dates as special dates related to the Earth's axial tilt:
March 21 - Spring Equinox
This is the time when the sun crosses the celestial equator. Day and night are of equal length throughout the world. This date marks the beginning of spring for the northern hemisphere and the beginning of autumn for the southern hemisphere.
June 21 - Summer Solstice
It marks the beginning of summer in the Northern Hemisphere. On this date, the sun reaches its highest point along the northern latitude, resulting in the longest daylight hours. In the Southern Hemisphere, this date marks the beginning of winter.
September 23 - Autumn Equinox
This is another time when the sun crosses the celestial equator. Again, day and night are of equal length. It marks the beginning of autumn in the Northern Hemisphere and the beginning of spring in the Southern Hemisphere.
December 21 - Winter Solstice
In the Northern Hemisphere, it marks the beginning of winter. On this date, the sun reaches its lowest point along the southern latitude, resulting in the shortest daylight hours. In the Southern Hemisphere, this date marks the beginning of summer.
The Effects of Earth's Axial Tilt and Annual Rotation
The Earth's axial tilt and annual rotation are the main factors that create the seasons. If there were no annual rotation, the Earth would not rotate around the Sun, and the axial tilt would not affect the amount of sunlight the Earth receives from the Sun. The combination of these two factors results in seasonal changes on Earth.
What are the consequences of the Earth's axial tilt?
The consequences of the Earth's axial tilt can be summarized as follows:
The formation of seasons: Due to the Earth's tilt of 23.44 degrees, the angle at which the sun's rays strike the planet changes throughout the year, creating the seasons.
Day lengths: The Earth's axial tilt causes summers to be longer and winters to be shorter.
Day and night at the poles: Due to the Earth's axial tilt, there is 6 months of daylight at one pole and 6 months of night at the other.
Sea and air currents: Due to the oblique angle, the sun's rays fall at different angles, creating temperature differences in the seas and atmosphere, and consequently, currents are formed.
Ecosystem: Seasonal changes affect the life cycles of plants and animals, triggering events such as migration, hibernation, and pollination.
Is the Earth's axial tilt changing?
Yes, the Earth's axial tilt is changing and will continue to change. Fracastoro was the first to realize that the axial tilt was decreasing at a relatively constant rate in 1538. The change in the Earth's axial tilt over time is caused by the gravitational forces from the Sun, Moon, and other planets. The Earth's axial tilt is decreasing very slowly in a cycle of approximately 41,000 years. It was at its maximum tilt approximately 10,000 years ago and will reach its minimum tilt in about another 10,000 years.
What would happen if the Earth didn't have an axial tilt?
In short, let's briefly list what would happen if the Earth did not have an axial tilt:
There would be no seasons.
The sun's radiation would be evenly distributed across the Earth.
Except for the poles, every day would be 12 hours long, everywhere.
More sunlight fell on the equator, and less on the poles.
The temperature difference between the equator and the poles would be less than it is now.
The weather would be more stormy in the mid-latitudes.
Regions around the equator experienced an eternal summer.
The sun's movement across the sky always followed the same path.
At the poles, the sun appeared to revolve around the horizon and never truly rose or set.
The poles would become warmer, and sea levels would rise.
Solar and lunar eclipses would occur less frequently.
The increasing temperature would indirectly change the dynamics of the atmosphere.
Due to the Earth's axial tilt, the height of the sun in the sky is related to latitude. At the equator, the sun is always high, while at the poles, the sun is lower above the horizon. Therefore, if there were no axial tilt, most of the energy would be concentrated at the equator, while less would reach the poles. As a result, more energy would be transferred from low to high latitudes, and there would be more air movement in the mid-latitudes.
Also, if there were no axial tilt, the sun would always reach its zenith point (directly overhead) at noon near the equator. This would cause a significant increase in annual radiation and temperature at the equator, making it an extremely hot region. As you migrate from the equator to higher latitudes, the apparent path of the sun's sunrise and sunset would get closer to the horizon. At the poles, the sun would simply revolve around the horizon and would never be seen rising or setting. The temperature there, which is almost constant, would still be much lower than elsewhere, but certainly warmer than it normally is. The ice at the poles could melt completely, so we can expect sea levels to rise.
What happens if the Earth's axial tilt increases?
If the Earth's axial tilt increased, one of the biggest consequences would be hotter summers and colder winters. In addition, the equatorial climate zone would expand, resulting in tropical rainforests spreading over a wider area. Furthermore, an increased axial tilt means more sunlight would reach the poles, accelerating the melting of polar ice and raising sea levels.
In addition to all this, we also need to consider frozen bacteria or viruses due to the increasing melting in the polar regions. Every living thing on Earth would have to encounter new bacteria and viruses. We would give the same answer to a question like what would happen if the Earth's axial tilt were 30 degrees. Because we have enough information to say that if the Earth's axial tilt decreases, it will specifically affect this, and if it increases, it will specifically affect that.
What would happen if the Earth's axial tilt decreased?
What would happen if the Earth's axial tilt decreased , for example, if the Earth's axial tilt were 15 degrees? First, there would be fewer seasonal changes; the Earth would experience a major shift. The North Pole and Antarctica would receive sunlight every day of the year, and the extreme cold in these regions would cease to exist. They would still be the coldest regions on Earth, but they would not have 24-hour days or the midnight sun. Since night and day would always be the same length in polar regions and high altitudes, these and other cold regions would likely become warmer. The probability of snowfall would increase, but it would occur closer to the polar regions. If the temperature changes, ocean currents and air currents would naturally change as well. In short, if the Earth's axial tilt decreased, we would first experience major seasonal changes and then a warmer Earth. Would humans still exist as a result of those changes? Perhaps yes, perhaps no.
As Galaxy Explorer, I have tried to answer your questions such as what is axial tilt, how does it work, what are the consequences of axial tilt, what would happen if there were no axial tilt, and what is the Earth's axial tilt in degrees, in the shortest and most understandable way. I hope that our Earth's axial tilt never undergoes a major change so that these boundless space explorations can continue. We will continue to do so!
