When Earth is closest to the sun, the Northern Hemisphere is in winter. (20 points)
A. Why is this true? (10 points) The North Pole of the Earth’s axis is tilted away from the sun which causes it to be winter in the northern hemisphere.
B. Given the effects of precession, will this still be the case in 13,000 years? Explain your answer. (10 points)
The Correct answer and Explanation is:
A. Why is the Northern Hemisphere in winter when Earth is closest to the sun?
The Northern Hemisphere experiences winter when Earth is closest to the sun (a point called perihelion) due to the tilt of Earth’s axis. Earth’s axis is tilted at about 23.5 degrees relative to its orbit around the sun. This tilt means that different parts of Earth receive varying amounts of sunlight throughout the year, resulting in seasons. During winter in the Northern Hemisphere, the North Pole is tilted away from the sun. Even though Earth is closer to the sun during perihelion, the sunlight strikes the Northern Hemisphere at a lower angle, spreading the energy over a larger area, leading to cooler temperatures. Additionally, the days are shorter, further reducing the amount of solar energy that reaches the surface. Thus, despite Earth being closer to the sun, the reduced angle and shorter days result in winter conditions.
B. Will this still be the case in 13,000 years, given the effects of precession?
No, in about 13,000 years, the Northern Hemisphere will not be in winter when Earth is closest to the sun due to the effects of axial precession. Precession is the slow, gradual wobble in Earth’s axis of rotation, which causes the orientation of Earth’s tilt to shift over a 26,000-year cycle. This means that the positions of the equinoxes and solstices slowly shift relative to Earth’s orbit around the sun. Currently, perihelion occurs in early January, during Northern Hemisphere winter. However, as precession progresses, in approximately 13,000 years, perihelion will occur in the Northern Hemisphere’s summer instead of winter. At that time, the North Pole will be tilted toward the sun during perihelion, leading to warmer summers in the Northern Hemisphere when Earth is closest to the sun. Thus, precession will reverse the seasonal relationship between perihelion and the Northern Hemisphere’s winter, making it summer when Earth is closest to the sun.
Precession affects the timing of seasons in relation to Earth’s orbital position, but it does not change the overall length of seasons or the axial tilt itself. This natural cycle alters how the sun’s energy is distributed over long periods, creating shifts in climate patterns.