Question

Earth is closest to the Sun during which season in the northern hemisphere? A) spring C) winter B) summer D) fall

Short answer

Earth is closest to the Sun during winter in the northern hemisphere.

Step-by-step solution

Identify Earth's Orbital Motion

Understand that Earth travels around the Sun in an elliptical orbit, meaning there are points when it is closest or farthest from the Sun during its orbit, these points are known as perihelion and aphelion, respectively.

Locate Perihelion

Perihelion is the point in Earth's orbit where it is nearest to the Sun. This occurs annually around the beginning of January.

Align Perihelion with Seasonal Patterns

Recognize that the beginning of January corresponds to the winter season in the northern hemisphere. Therefore, Earth is closest to the Sun during winter.

Confirm Alignment

Verify the seasonal correlation by considering that perihelion is an astronomical event that does not directly influence the seasons, which are primarily determined by Earth's axial tilt.

Key concepts

Perihelion and Aphelion

As Earth orbits around the Sun, it doesn't follow a perfect circle. Instead, it travels in an elliptical path. This means there are moments when Earth is closest to the Sun, called **perihelion**, and moments when it's farthest away, known as **aphelion**.

At perihelion, Earth is about 147 million kilometers from the Sun. This typically occurs in early January. Conversely, at aphelion, occurring in early July, Earth is roughly 152 million kilometers away from the Sun.

These distances illustrate the slight variance in our planet's proximity to its star. Despite such changes, they don't directly cause our seasons. Instead, they slightly alter solar energy received on Earth, marginally affecting temperatures. Interestingly, the northern hemisphere experiences winter when Earth is closest to the Sun, a surprising fact for many.

Seasonal Changes

Despite reaching perihelion in January, the northern hemisphere experiences winter. Seasons aren't determined by Earth's distance from the Sun, but rather by the tilt of the Earth's axis.

This axial tilt means different parts of Earth receive varying amounts of sunlight throughout the year. Here is why seasons occur:

• During winter, one hemisphere tilts away from the Sun, resulting in shorter days and less direct sunlight, thus colder temperatures.


• In summer, the same hemisphere tilts toward the Sun, leading to longer days, more direct sunlight, and warmer temperatures.

Spring and autumn mark transitions where daylight and temperatures are more balanced. Thus, summer and winter occur based on this tilt, not the Earth's nearness to the Sun.

Earth's Axial Tilt

The axial tilt of Earth—approximately 23.5 degrees relative to its orbit around the Sun—is the driving force behind the changing seasons. This tilt causes different angles of sunlight to hit various parts of the Earth as it revolves around the Sun.

When the northern hemisphere tilts toward the Sun, it experiences summer, with longer daylight hours and warmer climates. This scenario flips when it's the southern hemisphere's turn, bringing winter to the north.

Furthermore, Earth's axial tilt ensures that each hemisphere gets a chance to experience all seasons. Key points to understand about axial tilt include:

• Without axial tilt, we wouldn't have the diversity of seasons.
• Axial tilt remains constant as Earth orbits the Sun, making it the primary reason for seasonal variance.

As Earth continues its journey around the Sun, it's this tilt that paints a colorful tapestry of climates across the globe.