On July 5, 2024, at around 1 a.m., Earth reached its farthest point from the Sun, known as aphelion. This annual event raises an intriguing question: why are we experiencing summer heat when our planet is at its greatest distance from the Sun?
Understanding Aphelion
During aphelion, Earth is about 94.5 million miles (152 million kilometers) away from the Sun. This contrasts with perihelion, which occurs in early January, when Earth is closest to the Sun at approximately 91.4 million miles (147 million kilometers).
The difference of about 3 million miles (5 million kilometers) might seem significant, but it accounts for only a roughly 3% variation in distance, which is not enough to drastically affect our seasonal temperatures.
Johannes Kepler, a 17th-century German mathematician, explained this phenomenon through his laws of planetary motion, which describe how planets orbit the Sun in an elliptical shape, causing these varying distances. As the Earth travels along this elliptical orbit, it experiences changes in distance from the Sun that contribute to variations in solar radiation received.
However, these changes are relatively minor compared to the primary factor that determines our seasons: the tilt of Earth’s axis.
Reasons for the Seasons
The distance from the Earth to the Sun does affect the amount of solar radiation received, but it is not the primary factor determining our seasons. The tilt of Earth’s axis is the critical element. Earth’s axis is tilted by approximately 23.44 degrees, influencing how much sunlight each hemisphere receives throughout the year.
This axial tilt means that different parts of Earth receive varying amounts of sunlight at different times of the year, creating the seasons.
In July, the Northern Hemisphere is tilted towards the Sun, resulting in longer days, shorter nights, and the Sun appearing higher in the sky. This tilt ensures that the Northern Hemisphere receives more direct sunlight, leading to warmer temperatures and the summer season.
Conversely, the Southern Hemisphere is tilted away from the Sun, experiencing winter with shorter days and longer nights. Earth’s annual aphelion occurs two weeks after June’s solstice, the beginning of summer in the Northern Hemisphere and winter in the Southern Hemisphere.
The Role of Earth’s Tilt
Earth’s axial tilt ensures that the Northern Hemisphere enjoys its warmest weather when the planet is actually farthest from the Sun. During the aphelion, the increased exposure to direct sunlight in the Northern Hemisphere leads to the hot summer temperatures we experience.
This is also why, despite being closer to the Sun during perihelion in January, the Northern Hemisphere experiences winter. The tilt of Earth’s axis means that the Northern Hemisphere is then angled away from the Sun, resulting in shorter days, longer nights, and less direct sunlight.
The distance from the Earth to the Sun does not determine the seasons we experience on Earth. Instead, it is the tilted axis on which our planet spins that plays the crucial role. This understanding explains why, despite the varying distances during aphelion and perihelion, the primary driver of seasonal changes remains the axial tilt.
Additional Insights from Experts
Understanding the intricate relationship between Earth’s orbit, axial tilt, and seasonal changes enhances our appreciation of the complex dynamics that govern our planet’s climate. The Seattle Times highlights that “aphelion happens every year as the summer is underway,” emphasizing the regularity of this celestial event.
This annual occurrence, while fascinating, underscores the importance of axial tilt over orbital distance in determining seasonal temperatures.
Moreover, the concept of aphelion and perihelion offers valuable insights into the mechanics of our solar system and the factors influencing Earth’s climate. By studying these phenomena, scientists can better predict and understand the broader patterns of climate and weather that affect our planet.
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
