Solar System

Why Is The Earth Tilted?

The Earth is tilted on its axis by 23.5 degrees due to a collision with a Mars-sized asteroid approximately 4.5 billion years ago.

Josh Universe
Dec 20, 2022
4 min read
Earth

When dinosaurs were ruling Earth, scientists say. Astronomers suspect that the tilt was caused by an impact on an Earth-size planet billions of years ago, shortly after the formation of Uranus.

In older models, a very steep axial tilt was caused by big bang angles and has been constant over time. The Earth's axial tilt, also known as ecliptic obliquity, is approximately 23.5 degrees.

Axial tilt is the obliquity of Earth's axis relative to Earth's axial plane in its orbit around the sun. Instead of rotating in the direction that would make Earth's axis perpendicular to its orbital plane, it is tilted at an angle of 23.45 degrees to the perpendicular.

Earth spins on an axis tilted 23 1/2 degrees to its orbital plane. Earth may have hit a different proto-planet and was tipped during that process. Earth's axis looks steady, but it is slowly twitching, almost like a spinning top.

Because of the way its axis is tilted, the Sun is higher when you are in a part of the earth that has its axis pointed more toward the Sun and lower in parts of the Earth that have their axis pointed away from the Sun.

During the 24 hours that the Earth takes to revolve once on an axis, each point on its surface faces toward the sun sometimes and away from the sun some of the time. For both hemispheres, Earth is at a distance of 90 degrees from the sun on about March 21, then again around September 21. Around March 21 and September 21, Earth is at an angle of about 90 degrees away from the sun (right angle).

On December 21, the Sun appears lower in the sky, at its lowest angle from Earth, and we get less sunlight and heat. During northern Hemisphere summer, the Earth is tilted towards the sun, so poor southern poles get the least amount of sunlight -- parts are dark for more than 24 hours.

When either Pole has tilted away from the Sun, half of the planet gets less sunlight and is wintering. When one of the poles points more towards the Sun than the other, that half of the planet gets more sunlight than the other half, and it is summer in that hemisphere.

The Earth is not tilted towards the sun, nor is it tilted away; it is more tilted toward the side of the earth, and thus the areas on the globe receive an equal amount of sunlight and darkness. The further from Earth's equator one gets, the greater differences in seasons and sunlight. Even if the place across the planet from where you are may receive exactly the same amount of sunlight right now that your location does during the summer, the weather may not match what you are used to.

When the Sun is lower in the sky, the light is spread more thinly across the surface of the Earth, allowing less heat to be absorbed (per square inch). What might be a surprising observation is that average air temperatures are lower on days with more direct sunlight.

Without obliquity, the sun's angle is always equal; thus, Earth's equator experiences similar amounts of heat and light all year. The tilt direction relative to the Sun- our light and heat source- changes when we orbit around the Sun. Tilt means our planet's north and south poles are not directly up and down as the earth orbits the sun; they are always tilted.

As Earth moves through an almost spherical (very slight eccentricity in ellipse) orbit around the sun, the northern hemisphere may tilt towards the sun or away, depending on its orbital location. The seasons are changed by Earth's angle of tilt--23.5 degrees--relative to our orbit around the sun. Instead, Earth has seasons because our planet's rotational axis tilts 23.5 degrees in relation to our orbital plane, which is Earth's orbital plane around the sun.

Day-to-day changes in light and temperature are caused by the Earth's rotation, while the changes in seasons are caused by Earth's tilt. Small changes in the Earth's rotation, tilt, and orbit during those long periods of time can alter how much sunlight is received (and thus absorbed and re-radiated) to different parts of the planet. Earth's spin, tilt, and orbit all affect how much of the sun's energy is received in a given area of the Earth, depending on latitude, daytime, and season.

Because a young Earth is orbiting the Sun at an angle, the amount of solar energy reaching various parts of our planet changes throughout the course of the year. Earth's distance from the sun changes over the year, and logically, one might think that a rise or fall in the solar-planet distance might trigger seasonal changes.

Small changes in Earth's angle of tilt and its shape as it orbits the sun have caused climate changes for tens of thousands to one hundred thousand years, but they have not caused any climate changes to date. How far Earth's axis is tilted toward the Sun, or away from it, changes over time, in cycles that last about 41,000 years. Periodic movements of the Moon and the Earth within the orbit of the Earth produce a much smaller (9.2 arcseconds) and shorter-period oscillation of the Earth's rotational axis, known as nutation, adding a periodic component to the obliquity of the Earth.

As the Earth rotates on its axis, producing nights and days, it also moves around the Sun in an elliptical (elongated circle) orbit, taking approximately 365 1/ 4 days to complete.

An asteroid as large as Mars struck the young Earth while still in the process of formation. The impact is how the moon formed and the Earth got its axial tilt. New evidence suggests that a large impact of this type also sent Earth in a very narrow orbit, with an extremely sharp axial tilt, almost perpendicular to the equator.

Unlike in the torch experiments, the tilt did not affect how much radiation reached the suns surface. Instead, our seasons vary because Earth is tilted relative to Earth's axis, and the tilted angle causes the Northern and Southern hemispheres to swap places over the course of a year, capturing more direct sunlight and heat from the Sun.

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