The seasons and precession

It is a common misconception that the seasons are caused by Earth being closer or farther from the Sun at different places along the planet’s “elliptical” orbit. This is not the cause of the seasons. Mathematically, a circle is a type of ellipse. Earth’s orbit is so nearly circular that the small variation in distance from the Sun does not explain the large temperature changes that occur with the seasons. Nor does ellipticity explain why summer in the northern hemisphere occurs at the same time as winter in the southern hemisphere. This could not be true if summer were caused by Earth being closer to the Sun. Read the text aloud
Earth's rotational axis is tilted by 23.4° relative to its orbital axisThe seasons are caused by the orientation of Earth’s rotational axis relative to the plane of its orbit around the Sun. The Earth rotates about its axis once every 24 hours, and it orbits around the Sun once every year. Earth’s rotational axis, however, is not perpendicular to its orbital plane. The Earth’s rotational axis is tilted by 23.4° relative to the orbital axis about which it revolves around the Sun. Read the text aloud Show The tropics
Seasons are caused by the tilt of the Earth's rotational axisBecause of the tilt of the Earth’s axis, in January the North Pole tilts 23.4° away from the Sun. This reduces the intensity of sunlight creating winter in the northern hemisphere. Six months later, in June, the North Pole tilts toward the Sun. This increases the intensity of sunlight, making summer. The opposite is true in the southern hemisphere.

The tilt of Earth’s axis also causes polar regions of our planet to have extremes of day and night near the summer and winter solstices. Near the North Pole at the summer solstice, the Sun never sets! This creates 24 hours of daylight. At the same time but near the South Pole, the Sun never rises, creating 24 hours of night. Read the text aloud
A strange thing happens to the Earth’s axis of rotation: It rotates slowly around the Earth’s orbital axis, tracing a 46.8° wide circle on opposite sides of the sky. It takes a full 26,000 years for a complete cycle of this precession of the Earth’s axis. Read the text aloud Show What is your astrological sign?
Precession of a gyroscopeYou don’t have to wait 26,000 years to see precession at work. Just use a gyroscope, which you can buy for less than $10! Tilt the gyroscope axis with respect to the vertical—or even point it horizontally. Start the rotor spinning and place one end on its stand. The gyroscope’s rotational axis will precess about the vertical. This precession occurs as a result of the interaction between the angular momentum of the gyroscope and the torque exerted by the gravitational force. Read the text aloud
The Arctic Circle represents the northernmost region of the Earth where the Sun can remain above the horizon for 24 hours a day at some time during the year (i.e., around the time of the summer solstice).
  1. What is the latitude of the Arctic Circle?
  2. If the Earth’s rotational axis were parallel to its orbital axis, how big would the Arctic Circle be?
If the Earth’s rotational axis were not tilted with respect to its orbital axis, would the axis still precess? Show

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