Illusions of the Seasons: Part 2

Jesse Warner

In our first season’s discussion we learned how the Earth’s distance from the Sun has very little effect on the seasons.  In this discussion, we will dispel another common misconception about the seasons. 

Misconception #2:   There are two days in the year when the Sun is directly over the North or South Poles of Earth.

During the Summer Solstice each year, the North Pole (and all areas north of 66° N) experience 24 hours of daylight, and the South Pole (and areas south of 66° S) experience 24 hours of darkness.  During the Winter Solstice each year, this effect is reversed with the South Pole experiencing daylight and the North Pole experiencing darkness.  It would be easy to assume that the Sun must be directly over the Poles when they experience 24 hours of daylight.  This, however, is not the case.

Earth’s rotational axis is pointed nearly at Polaris, the North Star, tilted about 23.5° from vertical relative to its orbit around the Sun. Earth maintains the same angle of inclination throughout its orbit.  Earth’s surface angle to the Sun, however, does change throughout the year.  As we orbit the Sun, the North Pole leans in the direction of the Sun for a portion of the year (summer) and it leans away from the Sun for a portion of the year (winter).350px-Solstice_diagram

The Sun will never be directly above either of the poles and in fact only gets to a maximum height of about 23.5° above the horizon at either the north or south pole.  At the North Pole, the Sun is permanently above the horizon during the summer months and permanently below the horizon during the winter months causing night-less summers and day-less winters.  The reverse is true at the South Pole.  

To get the full picture, let’s look at some other locations around the world.  Take the Equator, for example. The day length is roughly 12 hours at the Equator all year long.   From the Equator to the Poles, all points in between experience different amounts of daylight depending on their distance from these locations (their latitude).  

So what does this have to do with the seasons?picture jess2

As we orbit the Sun, Earth’s surface receives varying intensities and durations of sunlight. In Utah, June is when the Sun climbs high in the sky (about 73°) and our part of  Earth receives a strong concentration of sunlight.  Earth has more time (about 15 hours) to absorb the Sun’s energy during the day while there is less time at night (about 9 hours) for that energy to radiate back into space. This is when we experience our warm summer months.  In December, the Sun doesn’t reach nearly as high in the sky (about 26°), so the rays of light spread out as they cover the ground. Therefore, the Sun’s energy is less efficient at warming our part of Earth’s surface.  That fact, coupled with the fact that we have less hours (about 9 hours) to absorb the Sun’s energy and more hours (about 15 hours) for that energy to radiate back to space makes for our cold winter months.

In our next discussion, we will look at the next common misconception about the seasons and discuss some activities that you can do to help you better understand the seasonal changes here on Earth.

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2 thoughts on “Illusions of the Seasons: Part 2

  1. Pingback: Illusions of the seasons: Part 1 « Clark Planetarium

  2. Pingback: Illusions of the Seasons: Part 3 « Clark Planetarium

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