The Earth is spherical in shape; it is an established fact, backed by several pieces of evidence. The equatorial circumference of the Earth is 24,897 miles, while its polar circumference is less than 83 miles than that of the equatorial circumference. This shows the Earth is not a perfect sphere. The Earth is flattened at both ends (poles) like an orange. This shape is called Geoid (Earth-like).
There are many ways to prove that the Earth is spherical. They are as follows:
Circumnavigation of the Earth:
The first voyage by Sir Magellan around the world proved that the Earth, if not a sphere, was not a shape with abrupt edges. It was also discovered that once you start at one point, you are bound to reach that place completing a circular path. Modern-day air routes and ocean navigation are based on the assumption that the Earth is a sphere.
The Circular Horizon:
The distant horizon as seen from a ship, a cliff, or a landmass is often seen as circular in shape. In fact, with an increase in altitude, the circular horizon broadens. This is a feature only of a spherical body.
Ship’s Visibility:
When a ship appears over a distant horizon, the mast of the ship is seen first, followed by the hull. Similarly, when the ship leaves the harbor, the disappearance of the ship over the curved surface is gradual. This would not have happened had the Earth been flat; the entire ship would be visible or obscured from view.
Sunrise and Sunset:
The Sun rises and sets at different times at different places in the world. As the Earth rotates from the west direction to the east direction, places in the east see sunrise before the places in the west. Had the Earth been flat, the entire Earth would have had sunrise and sunset at the same time.
The Lunar Eclipse:
The shadow cast by the Earth on the Moon is always circular during the lunar eclipse. It takes the shape of an arc of a circle on the Moon.
All Planetary Bodies Are Spherical:
When looking through a telescope, all the planetary bodies like the Sun, the Moon, and other planets appear circular or spherical in nature, no matter from whichever angle they are viewed. Earth, by analogy, cannot be the only exception.
Aerial Photographs:
The pictures taken by satellites always show the curved edge of the Earth. This is the most convincing and modern proof of Earth’s sphericity.
Driving Poles on Level Ground on a Curved Earth:
Engineers driving poles of equal length at regular intervals on the ground find that they do not get a perfect horizontal level. The center pole normally projects slightly above the poles on either side because of the Earth’s curvature.
The Earth’s Movement
The Earth moves in space in two different ways: rotation and revolution.
Rotation: Earth rotates on her own axis from west to east direction once every 24 hours (approximately). This causes the phenomenon of day and night. When the Earth rotates on her axis, only one portion of the Earth gets sunlight. The area receiving sunlight experiences daylight. The other side of the Earth, away from the Sun, experiences darkness or night. Because of the west-to-east rotation of the Earth, every part of the Earth will receive sunlight sometime or the other. When the Earth emerges from darkness to gradual light, it is called sunrise, and later, when the Sun’s rays give way to darkness, that place experiences sunset.
Revolution: Earth also revolves around the Sun in its orbit once every 365 days. This revolution around the Sun constitutes a year. This revolution also causes seasonal variation. It is important to note that the Sun is a stationary body. The Earth revolves around the Sun, spinning on an elliptical orbit at a speed of 18.5 miles per second. One complete revolution around the Sun takes 365 ¼ days. Thus, a normal year is taken to be of 365 days. The ¼ of a day is added to the year once every four years to form one whole new day. This added day every four years is called the Leap Year.
Varying Lengths of Day and Night: The Earth’s axis is inclined to the plane of the ecliptic at an angle of 66 ½°. Because of this tilt in the axis, there are varying lengths of days and nights. At a given time of the year, different places on the Earth’s surface will have varying amounts of daylight. In the Northern Hemisphere during winter, nights become progressively longer as you move northward. At 66 ½° N, in the Arctic Circle, there is constant darkness for a whole day in mid-winter. (Winter Solstice, December 22). On the other hand, in summer, daylight is longer. In mid-summer (Summer Solstice, June 21), sunlight is constant in the Arctic Circle for the whole day. In the Southern Hemisphere, however, these patterns are reversed because summer in the Northern Hemisphere corresponds to winter in the Southern Hemisphere and vice versa.
The Altitude of the Midday Sun
On March 21 and September 21, the Sun is directly overhead at the Equator. These days are known as equinoxes. The day and the night are equal all over the world during equinoxes. On June 21, the Sun is vertically overhead at the Tropic of Cancer (23½° N). This position of the Sun is called the Summer Solstice and marks the longest day in the Northern Hemisphere. On December 22, the Sun is overhead at the Tropic of Capricorn (23½° S), which marks the Winter Solstice. During the Winter Solstice, the Northern Hemisphere experiences its shortest day and longest night, while the Southern Hemisphere has its longest day and shortest night.
Seasonal Changes and Their Effects on Temperature
During the summer months, the Sun appears high in the sky, and the rays are vertical. These vertical rays give more heat per unit area, causing higher temperatures. The days also become longer. Conversely, during winter, the Sun’s rays fall obliquely, are spread over a larger area, and hence are less effective in heating. As a result, temperatures drop, and days become shorter.
Dawn and Dusk
Dawn refers to the short interval after the Sun rises, but before there is full daylight. Dusk refers to the short interval between sunset and complete darkness. The red sky at both dawn and dusk is due to the scattering of light by atmospheric dust particles. Even when the Sun is below the horizon, diffused or refracted sunlight continues to reach us. The periods of dawn and dusk are shorter near the equator because the Sun’s apparent path is nearly vertical. On the other hand, the periods are longer in temperate and polar regions because the Sun’s apparent path is more oblique.
What is the shape of the Earth?
The Earth is spherical in shape, but it is not a perfect sphere. It is slightly flattened at the poles, giving it a shape called Geoid.
How does circumnavigation prove the Earth’s spherical shape?
Circumnavigation, such as Magellan’s first voyage around the world, demonstrates that the Earth is spherical as one can travel in a circular path and return to the starting point without encountering abrupt edges.
Why is the horizon circular when viewed from a height?
The horizon appears circular when viewed from a height because of the Earth’s curvature, a characteristic feature of a spherical body.
What happens to a ship’s visibility on the horizon, and what does it signify?
As a ship approaches the horizon, its mast is seen first, followed by the hull. When leaving, the ship disappears gradually, which signifies the Earth’s curved surface.
How does the lunar eclipse confirm the Earth’s spherical shape?
During a lunar eclipse, the Earth’s shadow on the Moon appears as a circular arc, confirming the Earth’s spherical shape.
Why do different places have sunrise and sunset at different times?
Different places experience sunrise and sunset at different times because the Earth rotates from west to east, exposing parts of its surface to the Sun in sequence.
What are the main movements of the Earth?
The Earth has two main movements: rotation, which causes day and night, and revolution, which creates the year’s seasonal variations.
How does Earth’s rotation cause day and night?
Earth’s rotation causes only one side of the planet to face the Sun at a time, resulting in daylight on that side and darkness on the other.
How does Earth’s revolution lead to seasonal changes?
Earth’s revolution around the Sun in an elliptical orbit, combined with its tilted axis, leads to varying lengths of days, nights, and temperatures, creating distinct seasons.
What are equinoxes and solstices?
Equinoxes occur when the Sun is directly overhead at the equator, resulting in equal day and night worldwide (March 21 and September 21). Solstices mark the Sun’s maximum tilt north or south, creating the longest and shortest days (June 21 and December 22).
Why does the Arctic Circle experience six months of daylight and darkness?
At the Arctic Circle, due to Earth’s tilt, there is continuous sunlight for six months during summer (around June 21) and complete darkness for six months during winter (around December 22).
How does the altitude of the midday Sun vary with seasons?
The midday Sun is vertical at the equator during equinoxes, directly overhead at the Tropic of Cancer on June 21 (Summer Solstice), and at the Tropic of Capricorn on December 22 (Winter Solstice).
What causes variations in the length of day and night?
The Earth’s tilted axis and elliptical orbit cause variations in the lengths of day and night, with longer days in summer and shorter ones in winter.
Why is summer warmer than winter?
In summer, the Sun’s rays fall vertically, concentrating heat on a smaller area, and days are longer, allowing more time for heating. In winter, the rays are slanted, spreading heat over a larger area, resulting in cooler temperatures.
What causes dawn and dusk?
Dawn occurs between sunrise and full daylight, and dusk happens between sunset and complete darkness. Both are caused by diffused or refracted sunlight when the Sun is below the horizon.
How does twilight vary with location?
At the equator, twilight is brief due to the Sun’s vertical path, whereas at higher latitudes, twilight is longer because the Sun rises and sets at an oblique angle.