Question

The \(23.5^{\circ}\) tilt of Earth on its north-south axis gives rise to the seasons (review Figure 2.5 ). How would the pattern of seasons differ if the Earth's tilt were \(90^{\circ}\) ? How would this influence the diurnal (night- day) cycle?

Short answer

Answer: If Earth's tilt were at \(90^{\circ}\), the Northern Hemisphere would experience endless daylight and summer, while the Southern Hemisphere would be in darkness and experience perpetual winter. The diurnal cycle would be drastically different for the two hemispheres, losing its meaning due to the absence of transitions between day and night in both hemispheres. This would lead to extreme and unchanging seasonal patterns and significantly impact life on Earth.

Step-by-step solution

Understanding Earth's Current Tilt and Seasons

The Earth's current tilt of \(23.5^{\circ}\) on its north-south axis is what causes the seasons. As the Earth revolves around the Sun, the tilt causes different parts of the Earth to receive varying amounts of sunlight throughout the year. This leads to the four seasons (spring, summer, autumn, and winter) that we experience. When the Northern Hemisphere is tilted towards the Sun, it receives more sunlight, resulting in summer for those living above the equator. At the same time, the Southern Hemisphere experiences winter because it is tilted away from the Sun and receives less sunlight. The situation is reversed when the Southern Hemisphere is tilted towards the Sun.

Discussing Earth's Tilt at \(90^{\circ}\) and Seasonal Changes

If Earth's tilt were at \(90^{\circ}\), the North Pole would be constantly facing the Sun and the South Pole would be facing away from the Sun. In such a scenario, the Northern Hemisphere would be experiencing endless daylight and summer, while the Southern Hemisphere would be in darkness and experiencing perpetual winter. Meanwhile, the equator would receive intermittent sunlight because the Earth would still rotate on its axis, resulting in a less predictable pattern of seasonal change at the equator, with rapidly fluctuating temperatures caused by the brief periods of sunlight and darkness.

Influence on Diurnal Cycle

The diurnal cycle refers to the day-night cycle caused by the Earth's rotation on its axis. With a \(90^{\circ}\) tilt, the diurnal cycle would be drastically different for the two hemispheres. In the Northern Hemisphere, the diurnal cycle would disappear, as there would be constant daylight and summer. There would be no night time, and the concept of a 24-hour day would no longer apply. The Southern Hemisphere would experience perpetual darkness or winter, with absolutely no sunlight reaching the area. Here too, the diurnal cycle would lose its meaning, as there would be no transition from day to night or vice versa. Overall, a \(90^{\circ}\) tilt would result in extreme and unchanging seasonal patterns and have a significant impact on the diurnal cycle and life on Earth.

Key concepts

Seasonal Changes

Seasonal changes on Earth result from its axial tilt and orbit around the Sun. Currently, Earth is tilted at approximately 23.5 degrees, which is primarily why we experience four distinct seasons: spring, summer, autumn, and winter.

If Earth were tilted at a stark 90 degrees, the planet would experience extreme seasons. The regions around the North and South Poles would be locked into continuous daylight or darkness. For half of the year, one pole would bask in unending sunshine, creating an eternal summer, while the other endured an endless night, a permanent winter devoid of direct sunlight.

This would mean no regular transition between the seasons for polar regions as we know them. The equatorial region, however, would face rapidly changing conditions with fluctuating patterns of light and temperature, a sharp contrast to the stable and predictable cycles we currently experience.

Diurnal Cycle

The diurnal cycle, known as the day-night cycle, is another direct consequence of Earth's axial rotation. In a 24-hour period, different regions of Earth rotate into and out of sunlight, giving us periods of daylight followed by darkness.

A hypothetical 90-degree tilt would bring an end to this daily rhythm for much of the planet. Places situated at high latitudes would either have permanent sunlight or darkness, depending on their pole's orientation toward or away from the Sun. The disappearance of the diurnal cycle in these regions would challenge all forms of life, as many biological processes are synchronized with the regularity of day and night.

Earth-Sun Relationship

The Earth-Sun relationship is a delicate dance that determines not just seasons, but also the availability of sunlight and the warmth of our climate. Earth's orbit is nearly circular, keeping the distance from the Sun relatively constant, while the axial tilt is responsible for the intensity of solar radiation across varying latitudes.

If Earth's axial tilt were to shift to 90 degrees, the relationship between Earth and the Sun would be radically different. The poles would either be perpetually sun-bathed or starved of sunlight, leaving the rest of the planet with drastically altered exposure patterns. This would dramatically affect global climate systems, ocean currents, and even weather patterns, leading to a world vastly different from what we are accustomed to.