Final answer:
Winter in the northern hemisphere occurs when Earth's axial tilt is oriented away from the Sun, around December 21st, causing shorter days and less direct sunlight. This axial tilt is the crucial factor in the changing seasons, not Earth's distance from the Sun.
Step-by-step explanation:
Understanding Earth's Seasons
The hypothesis that seasons are caused by Earth’s varying distance from the Sun is a common misconception. In reality, the tilt of Earth's axis is the primary reason for seasonal change. Earth's axial tilt is about 23.5° and remains pointed in the same direction throughout its annual orbit. This tilt causes different parts of Earth to receive varying amounts of sunlight during the year.
In the northern hemisphere, it is winter when Earth’s tilt is oriented away from the Sun. The winter solstice, occurring around December 21st, marks the point when the Sun is at its lowest arc in the sky and the daylight hours are shortest. Conversely, the northern hemisphere experiences summer when it is tilted toward the Sun, around June 21st, with longer daylight hours and more direct sunlight.
It is also important to note that during winter in the northern hemisphere, Earth is actually closest to the Sun, contrary to what some may believe. This proximity to the Sun does not translate into warmer weather due to the less direct sunlight received as a result of the axial tilt. Seasonal temperatures change more dramatically the further one moves away from the equator, where the difference in received sunlight becomes more pronounced.
As Earth continues its orbit, the consistent axial tilt means that the hemispheres experience opposite seasons - when it is winter in the northern hemisphere, it is summer in the southern hemisphere, and vice versa. The equinoxes, occurring in March and September, are when both hemispheres receive equal amounts of sunlight, resulting in approximately equal day and night duration.