Earth’s Orbit- Explanation with Diagram

Earth’s Orbit 

Introduction

The long-term pattern of weather in a certain area is called climate. Changes in weather can be seen from hour to hour, day to day, month to month or even from year to year. For periods of 30 years or more, different patterns of weather can be seen.  

Generally, climates are consistent, hence living things can adjust to them. For example: Polar bears have adjusted to remain warm in polar climates, whereas cacti have adapted to store water that help them to survive in dry climates.  

Climates change very slowly, over hundreds or even thousands of years. As climates change, living organisms in that particular area must adapt, relocate, or sometimes risk becoming extinct.  

Earth’s spin, tilt and orbit 

The amount of solar energy received by any particular region of the globe, depends on various factors such as latitude, time of day, and time of year, Earth’s spin, tilt and changes in the shape of orbit. Small changes in the angle of Earth’s tilt and the shape of its orbit around the Sun bring about changes in climate. 

The Earth takes an year to orbit the sun. It orbits the sunin an elliptical manner, and it’s tilted on its axis. All these factors change over time and they affect the amount of radiation we receive from the sun which in turn makes the Earth cooler or warmer.The rotation of the Earth causes daily changes in light and temperature, and the tilt causes seasonal changes. When the Earth orbits the Sun, it is pulled by the gravitational forces of the Sun, Moon, and large planets present in the solar system, mainly Jupiter and Saturn. Over long periods of time, the gravitational pull of other objects of solar system gradually changes the Earth’s spin, tilt, and orbit. Approximately in over 100,000 – 400,000 years, gravitational forces will gradually change the Earth’s orbit from circular to elliptical shape, as shown by the blue and yellow dotted ovals in the image given below. The direction of the Earth’s tilt shifts over 19,000 – 24,000 years. Furthermore, in 41,000 year cycles, there will be a change in tilting of Earth’s axis towards or away from the Sun. Small changes in Earth’s spin, tilt, and orbit over these long periods of time can change the amount of sunlight absorbed and re-radiated by different parts of the Earth.  

In the past, on various scales, changes in Earth’s spin, tilt, and orbit have affected the Earth’s system. Some of these changes involve: 

More or less amount of sunlight absorbed by different areas of the Earth’s surface can affect its temperature. 

Increasing or decreasing temperatures, can change the pattern of distribution of snow and ice cover. At higher altitudes, an increase in the snow and ice cover, increases the reflection of sunlight, which in turn reduces the amount of sunlight absorbed by Earth’s surface. 

Snow and ice cover affect the changes in the Earth’s system that includes the carbon cycle, and the amount of carbon (including the greenhouse gas carbon dioxide) transmitted between the atmosphere, biosphere, and ocean. 

Measurement of Earth’s Orbit 

There are three main things that cause the Earth’s natural climate cycles (Earth’s orbit around sun); they are eccentricity, obliquity, and precession. Collectively these three cycles are called ‘Miankovitch cycles.’ 

As per Milankovitch’s theory, the three cycles namely eccentricity, obliquity and precession combine to affect the amount of solar heat that reaches the Earth’s surface and later the climatic patterns, including glaciation periods (ice ages). The period between these changes can be tens or thousands of years (precession and axial tilt) or more than hundreds or thousands of years (eccentricity). 

The three Milankovitch Cycles affect the seasonality and position of solar energy around the Earth, thus affecting contrasts between the seasons. 

Eccentricity : 

When the Earth is closer to the Sun, the climate is warmer and this cycle also impacts the length of the seasons. The amount of a shape’s (Earth’s orbit) deviation from being a circle is called ‘eccentricity.’ 

Earth’s annual journey around the Sun is not completely in circular path, but it is very close to circular. Over a period of time, the gravitational force from our solar system’s two largest gas giant planets, i.e., Jupiter and Saturn, affects the shape of Earth’s orbit to change from just about circular to slightly elliptical. Eccentricity calculates the change in the shape of Earth’s orbit from a perfect circle to slightly elliptical. These changes causes the increase in the distance between Earth and the Sun. 

Due to eccentricity our seasons are slightly of different lengths, i.e, in the northern hemisphere, currently, summer is about 4.5 days longer than winters, and spring season is almost three days longer than autumns. When eccentricity decreases, the length of the seasons slowly comes to normal. 

When Earth’s orbit is at its most elliptic path, around 23 percent more solar energy reaches the Earth than when it is farthest from the Sun. Presently, Earth’s eccentricity is most circular ( least elliptic) and is decrasing very slowly, in a cycle that covers about 100,000 years. 

Due to the eccentricity cycle, the total change in global annual insolation is very small. Because changes in Earth’s eccentricity are relatively small, there  are relatively minor changes in annual seasonal climate. 

Obliquity : 

Obliquity is an astronomical word explaining the angle of tilt of the Earth’s axis of rotation, in other words obliquity is  defined as the angle of Earth’s axis of rotation as it moves around the Sun. Obliquity causes seasons on Earth. Since last million years, obliquity has changed between 22.1° and 24.5ﹾ perpendicular to Earth’s orbital plane. If the Earth’s axial tilt angle is greater, the seasons will be more extreme, because each hemisphere gets more solar radiation in its summer when the hemisphere is tilted toward the Sun, and less in winter, when it is tilted away. Larger tilt angles prefer days of deglaciation, i.e.,the melting and retreat of glaciers and ice sheets. All these impacts  are not consistent universally. For example: higher latitudes get a larger change in total solar radiation than areas that are nearer to the equator. 

Currently Earth’s axis is tilted 23.4ﹾ or nearly half way between its extremities, and very slowly this angle is decreasing in a cycle that covers about 41,000 years. Last time it was at its maximum tilt around 10,700 years ago and will go to its minimum tilt around 9,800 years from now. While obliquity decreases, it also helps to make our seasons milder, which results in increasingly warmer winters, and cooler summers. This slowly allow snow and ice at high latitudes to develop into large ice sheets. So as ice covering increases, it reflects more of the solar energy back into space that encourages even further cooling. 

Precession:  

When Earth rotates, it slightly vibrates upon its axis, like a spinning toy top. This vibration is due to tidal forces initiated by the gravitational effects of the Sun and Moon that cause Earth to swell at the equator, that affects its rotation. The tendency in the direction of this vibration compared to the fixed positions of stars is known as axial precession. The cycle of axial precession spans about 25,771.5 years. 

Axial precession causes extreme season in one hemisphere and moderate in the other hemisphere. Presently during winter season perihelion occcurs in the Northern Hemisphere and summer in the Southern Hemisphere. This causes summer season extreme summers in the Southern Hemisphere and moderate seasonal change in Northern Hemisphere. However, in around 13,000 years, axial precession will make these conditions to reverse, with the Northern Hemisphere experiencing more extreme solar radiation and the Southern Hemisphere experiencing more moderate seasonal changes. 

Summary

• The long-term pattern of weather in a certain area is called climate.
• Climates change very slowly, over hundreds or even thousands of years.
• Climate changes happen due to Earth’s atmosphere.
• The latitude, time of day, and time of year, Earth’s spin, tilt, and orbit change determines
  the amount of solar energy received by any particular region of the globe.
• The three main things that cause the Earth’s natural climate cycles (Earth’s orbit around sun) are eccentricity, obliquity, and procession.
• The collective name of these three cycles is ‘Milankovitch’ cycles.
• The amount of a shape’s (Earth’s orbit) deviation from being a circle is called
  ‘eccentricity.
• Obliquity is defined as the angle of Earth’s axis of rotation tilts as it moves around the
  Sun.
• The tendency in the direction of this vibration compared to the fixed position of stars is
  known as axial precession.