Question

Copy Figure 5.1. (a) Show that when the sun is in \(\mathrm{C}\) it is day everywhere within the arctic circle and night everywhere within the Antarctic. (b) Make a model of the earth by finding a globe or making a simple globe by taking a melon and drawing the equator, the tropics and the two polar circles. Take a strong torch and fit it such that its horizontal rays point to the centre of the globe. Give the globe a tilt of about \(23.5^{\circ}\). Reproduce the beginning of summer, autumn, winter and spring by rotating the globe. Find how the length of day changes.

Short answer

It's day everywhere within the Arctic Circle during the northern summer solstice, with opposite conditions in the Antarctic Circle. Use a torch and tilted melon to simulate Earth's seasons.

Step-by-step solution

Analyze Earth and Sun Position - Part (a)

To show that it's day everywhere within the Arctic Circle when the Sun is at the point C, understand the tilt of Earth's axis. The Earth is tilted at approximately 23.5° relative to its orbit around the Sun. At a certain point during the year (the summer solstice in the Northern Hemisphere), the North Pole is tilted towards the Sun. This means that the Arctic Circle is in continuous sunlight, while the Antarctic Circle is in continuous darkness since the South Pole is tilted away from the Sun.

Visualize Earth’s Features - Part (b)

To create a simple model of the Earth, use a melon as a globe. Draw a line around the middle to represent the equator. Mark the Tropic of Cancer and Tropic of Capricorn at 23.5° north and south of the equator, respectively. Draw the Arctic Circle at 66.5° north of the equator and the Antarctic Circle at 66.5° south.

Simulate Sunlight on Globe

Position a torch (acting as the Sun) such that its light rays are horizontal and directed at the center of the melon. Tilt the melon (globe) at approximately 23.5°. This simulates Earth's axial tilt.

Reproduce Seasons by Rotating the Globe

Rotate the melon around the torch to simulate Earth's orbit around the Sun. Position it so the North Pole is towards the torch to represent the summer solstice. Rotate it away to demonstrate the different seasons: autumn (when neither pole is tilted towards the Sun), winter (when the South Pole is tilted towards the Sun), and spring (similar side position as autumn).

Observe Day Length Changes

As you rotate the melon, observe how areas within the Arctic and Antarctic Circles go from constant daylight to darkness and vice versa. Note these changes during each solstice and equinox to understand how the length of day varies during the year.

Key concepts

Arctic Circle daylight

The phenomenon of continuous daylight in the Arctic Circle, known as the "Midnight Sun," is a fascinating result of Earth's axial tilt. When the sun is positioned in such a way that it shines directly onto the Northern Hemisphere, typically occurring around the summer solstice, the North Pole is inclined towards the sun. This orientation allows for sunlight to blanket the Arctic Circle throughout the entire day.
This period of endless daylight can last for months, depending on how close you are to the Pole itself. In regions near the Circle's boundary, the sun merely skims the horizon and never fully sets. This results in 24-hours of daylight or continuous twilight, an event that uniquely characterizes summer in these northern extremities.
Although this constant sunlight creates an extraordinary experience, it also demands adaptations in local flora, fauna, and human activities, as these must adjust to seemingly endless days.

Antarctic Circle darkness

In contrast, the Antarctic Circle experiences a period of continuous darkness when the sun is in the same position that provides constant light to the Arctic Circle. This event, often referred to as the "Polar Night," is caused by the South Pole being tilted away from the sun.
During this time frame, which occurs around the Northern Hemisphere's summer solstice, the sun remains below the horizon throughout the day within the Antarctic Circle. This results in 24 hours of darkness or twilight, creating a stark, frozen landscape bathed only in dim light or darkness.
Such prolonged nights influence the Antarctic ecosystem significantly. Life here must adapt to months without sunlight. Many species engage in unique survival strategies, such as energy conservation or migration to more hospitable areas where they can forage for food.

seasons simulation

Simulating the seasons is an excellent way to understand Earth's complex interplay of motion and light. By replicating the Earth's axial tilt and orbit using a simple globe or model, one can observe how different parts of the world receive varying amounts of sunlight throughout the year.
Start by creating a model of Earth, using a melon or similar object, marked with key latitudinal lines like the Equator, Tropic of Cancer, Tropic of Capricorn, Arctic Circle, and Antarctic Circle.
A torch or lamp representing the sun should be fixed in a position that allows its light to hit the globe's center. By tilting the globe at 23.5°—Earth's axial tilt—you can rotate it around the light to simulate annual seasons.
Notice how the angle of light changes. During the Northern Hemisphere's summer, the North Pole tilts towards the sun, contributing to longer daylight hours. Conversely, during winter, the South Pole faces the sun, and the Northern Hemisphere receives less light, leading to shorter days.

globe model creation

Creating a globe model is a hands-on approach to visualizing and understanding Earth's geographical and astronomical phenomena. Begin with a round object like a melon, which can symbolize the Earth.
Draw a line around the center to represent the Equator. Then mark the Tropic of Cancer and the Tropic of Capricorn, which are approximately 23.5° north and south of the equator, respectively. Further, indicate the Arctic Circle at 66.5° north and the Antarctic Circle at 66.5° south.
This model can be a powerful educational tool, making abstract concepts about Earth's tilt, rotation, and orbit more manageable. You'll observe how different regions of the Earth receive sunlight during various times of the year and how this translates into seasonal changes.
Using this model, one can gain a profound appreciation for the mechanics behind daylight variation and how they impact climates, ecosystems, and human life across the globe.