The changing of the seasons in the Northern Hemisphere is largely influenced by the tilt of Earth's axis and its orbit around the sun. Here’s how these factors contribute to seasonal changes:
1. Tilt of Earth's Axis
Earth’s axis is tilted at an angle of approximately 23.5 degrees relative to its orbital plane around the sun. This axial tilt is crucial because it affects the angle and intensity of sunlight that different parts of the Earth receive throughout the year.
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Summer: During summer in the Northern Hemisphere, which occurs around June 21 (the summer solstice), the North Pole is tilted toward the sun. This results in longer days and more direct sunlight, leading to warmer temperatures.
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Winter: Conversely, winter in the Northern Hemisphere occurs around December 21 (the winter solstice), when the North Pole is tilted away from the sun. This outcome results in shorter days and indirect sunlight, leading to cooler temperatures.
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Spring and Autumn: The equinoxes, around March 21 (spring) and September 23 (autumn), occur when Earth's tilt is such that the sun is directly above the equator. During these times, both hemispheres receive roughly equal amounts of sunlight, resulting in moderate temperatures.
2. Movement Around the Sun
Earth's orbit around the sun is an elliptical shape, but the effect of this shape is less important than the axial tilt when it comes to seasonal changes. The Earth's revolution around the sun takes about 365.25 days, leading to the yearly cycle of seasons.
- Even though Earth is closer to the sun in January (perihelion) and farther away in July (aphelion), the greater factor is the axial tilt. The distance cannot overshadow the significant impacts of sunlight angles and hours of daylight.
Summary
In summary, the tilt of Earth's axis results in varied sunlight angles and day lengths throughout the year, leading to seasonal changes. When combined with Earth's annual orbit around the sun, these effects create the distinct seasons experienced in the Northern Hemisphere: summer, fall, winter, and spring.