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ASTRONOMY: 8.
Explaining the
seasons of
the Earth - the tilted spin axis of the Earth as it orbits the Sun
Doc Brown's Physics exam study revision notes: The tilt in the spin axis changes the intensity of
sunlight through the year giving rise to periods of spring, summer,
autumn and winter with their different average temperature, weather
systems and the biological cycles of plants and animal life.
INDEX physics notes on
ASTRONOMY
8. Explaining the
seasons of
the Earth
As the Earth orbits the Sun it also spinning on an
axis of rotation roughly every 24 hours.
The spin axis is tilted at 23.5o away
from an imaginary vertical line from the plane of the Earth's orbit
around the Sun - see the diagram below.
This tilt in the spin axis causes the different
seasons on Earth by changing the intensity of the sunlight that
falls on the Earth's surface.
The shallower the sunlight angle, the less intense
the sunlight in terms of incoming radiation energy.
The steeper the sunlight angle, the more intense the
sunlight in terms of incoming radiation energy.
Position 1 corresponds to the autumn equinox in the
northern hemisphere.
Equal hours of night and daylight.
Equals the spring equinox in the southern hemisphere.
Moderate temperatures.
Position 2. corresponds to mid-winter in the
northern hemisphere.
Spin axis tilted away from the sun, so
reducing the intensity of sunlight and shorter length of
daylight.
Equals the mid-summer in the southern hemisphere, spin
axis tilted towards the sun.
The lowest temperatures on the Earth's
surface in the northern hemisphere.
The highest temperatures on the Earth's
surface in the southern hemisphere.
Position 3. corresponds to the spring equinox in
the northern hemisphere.
Equal hours of night and daylight.
Equals the autumn equinox in the southern hemisphere.
Moderate temperatures.
Position 4. corresponds to mid-summer in the
northern hemisphere.
Spin axis tilted towards the sun, so
increasing the intensity of sunlight and longer length of
daylight.
Equals the mid-winter in the southern hemisphere, spin
axis tilted away from the sun.
The lowest temperatures on the Earth's
surface in the southern hemisphere.
The highest temperatures on the Earth's
surface in the northern hemisphere.
Apart from the Earth's rotation giving the rising
and setting sun and the arced path in between, the position of the
sun in the sky is also influenced by the tilt of the Earth's spin
axis.
The sun is highest in the sky at midday in the
summer and at its lowest 'high point' point in the sky at midday,
mid-winter - see diagrams of the Sun's paths in the northern
hemisphere.
Path 1 of the sun represents mid-winter in the
northern hemisphere, shortest daylight time.
Path 2 of the sun represents its path at the
equinoxes.
Path 3 of the sun represents mid-summer in the
northern hemisphere, longest daylight time.
INDEX of my physics notes on
ASTRONOMY
Keywords, phrases and learning objectives for astronomy
Be able to explain the Earth's seasons with
reference to the tilt of the Earth's spin
axis.
Describe the difference in sunlight intensity
through the year causing the seasons of spring, summer, autumn
and winter cycles of weather affecting plant and animal life.
Use your
mobile phone in 'landscape' mode?
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