Describe how the seasons would be different if Earth's axis of rotation, rather than having its present \(23^{1 / 2^{\circ}}\) tilt, were tilted (a) by \(0^{\circ}\) or \((b)\) by \(90^{\circ}\)

Before we can analyze the hypothetical scenarios, let's briefly review how Earth's axial tilt plays a role in creating the seasons. Earth's axis of rotation is tilted at an angle of \(23.5^{\circ}\) relative to its orbital plane, the plane in which Earth orbits the Sun. This tilt causes different parts of Earth to receive different amounts of sunlight throughout the year, which results in the seasons.

If Earth's axis of rotation were tilted by \(0^{\circ}\), this would mean that there is no tilt and the axis would be perpendicular to the orbital plane. In this case, the amount of sunlight each part of Earth receives would not change throughout the year. As a result, there would be no seasonal variation in temperature and climate. Essentially, every part of Earth would experience the same weather conditions all year round. The polar regions would stay cold, the equatorial regions would stay hot, and the temperate regions would remain relatively mild.

If Earth's axis of rotation were tilted by \(90^{\circ}\), this would mean that the poles of the planet would be in line with the Earth's orbital plane, meaning that one pole would point directly toward the Sun and the other pole would point away from the Sun. The tilt would be maximal which would result in extreme seasonal variations. During part of the year, the Sun would be positioned directly over one of the poles, causing the other pole to experience total darkness. As the Earth orbits around the Sun, the sunlight would gradually encompass more of the planet, resulting in a short period of time when the entire surface of the Earth experiences daylight. However, the process would then reverse, with the newly illuminated pole eventually plunging back into darkness. This extreme axial tilt would lead to drastically different climates and light availability for each hemisphere. In essence, each hemisphere would alternate between a long period of complete daylight and a corresponding long period of complete darkness. Consequently, the variations in temperature and climate would be severe and likely have substantial consequences for life on Earth. In summary, Scenario (a) would result in no seasons and a uniform climate throughout the year, while Scenario (b) would lead to extreme and drastic seasonal variations, with long periods of total darkness and daylight for each hemisphere.