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Axial tilt and seasons

By changing the axis tilt, latitude, and orbital position, we compare the altitude and day length of the two hemispheres.

    E10 · Axial tilt and seasonsReady
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    Earth Science, Astronomy, Space / Principles and Exploration

    Axial tilt and seasons — principles and investigation

    The main cause of seasons is not a change in the distance between the Earth and the sun, but a change in solar conditions due to the tilt of the axis of rotation. Change axial tilt, latitude, and orbital position to compare day length and solar altitude. Use the same model to explain why opposite seasons occur in the Southern and Northern Hemispheres.

    How does it work?

    Axial tilt creates seasonal differences in sunlight. The two hemispheres have opposite seasons, and the sun may not set or rise at the poles.

    Key relationship

    h=90−|φ−δ| · cos H=−tan φ·tan δ

    Try this investigation

    1. The axis of rotation maintains the same direction in space throughout its revolution. Adjust latitude, inclination, and location to check the length of day in both hemispheres.
    2. Record the summer solstice, winter solstice, and spring equinox at 37.5° north latitude and compare the southern and central altitude and day length.
    3. Record the conditions in which only the axial tilt is changed to 0° and the midnight sun condition at the summer solstice of 70° north latitude.

    Interpreting your results

    At 37.5° N and an axial tilt of 23.5°, what is the solar-noon altitude at the June solstice?

    The summer solstice solar declination is δ=23.5°, so 90−|37.5−23.5|=76°. At the same time, 37.5° south latitude is 29°.

    Assumptions and limitations

    Assume a circular orbit and a fixed rotation axis. Atmospheric refraction, solar disk size, topography, and orbital eccentricity are omitted. A negative southern altitude means the sun is below the horizon. At a 0° tilt, the pole's center of the sun is along the horizon, so the length of the day is expressed by the convention of 12 h.