Seasons of Earth (Solstice and Equinox)
Our Earth is the only known planet to sustain life in the solar system; as it is present in the habitable zone around the sun. Our Earth is gravitationally bonded to the sun which makes us revolve around our star continuously. Our earth revolves around the sun (one complete round) over a period of one year. Over this period our earth encounters various situations; among which one of the main situations is seasons.
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Spring |
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Summer |
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Autumn |
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Winter |
Our earth mainly encounters four seasons, namely summer, winter, spring, and autumn. These seasons are commonly called as temperate seasons. Even though there are four seasons, some locations particularly near the equatorial regions experience different seasons as the rainy season, on behalf of winter. Before knowing about each of these seasons, let’s know how these seasons occur at the first step. We know that our earth is tilted at 23.4 degrees. First of all, we cannot map a sphere where it was tilted. Because whatever you turn a sphere, it looks the same all over the surface. But rotating a sphere in a particular direction, we can find out the direction of the sphere, it is pointing out. Our earth rotates at an inclined angle of 23.4 degrees. This inclined angle (otherwise can be said as inclined rotation) provides us all the magic including seasons. Without this inclined rotation, there would be no seasons or any other factors. This inclined rotation also makes each hemisphere to experience different seasons. These different seasons are caused by the rate of sunlight that falls on the tilted earth. By considering the below diagram you can observe what an inclined rotation is.
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Earth's Inclined Rotation |
Consider the earth in the below position. At this position, the northern hemisphere points away from the sun whereas the southern hemisphere points towards the sun due to the inclined angle. Now the northern hemisphere experiences the winter season as the light intensity spreads out over a larger distance and the southern hemisphere experiences the summer season as the light intensity concentrates over the surface. This type of season may start in December and last up to February.
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Winter in the Northern hemisphere and Summer in the Southern hemisphere |
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Winter in the Northern hemisphere and Summer in the Southern hemisphere |
As the earth continues to revolve around the sun, the earth completes its quarter journey around the sun after three months. At this point, neither the northern nor southern hemisphere faces more or less to the sun. Both the hemisphere faces the sun equally. At this point, the northern hemisphere will experience the spring season, and the southern hemisphere will experience the autumn season. This season may last from March to May. We will see later how the hemisphere distinguishes itself from spring and autumn; even both of them face the sunlight equally.
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Spring in the Northern hemisphere and Autumn in the Southern hemisphere |
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Spring in the Northern hemisphere and Autumn in the Southern hemisphere |
As the earth continues to revolve, it reaches the other side of the sun. Now the story is just the opposite, as the southern hemisphere faces away from the sunlight and the northern hemisphere faces towards the sunlight. Now the northern hemisphere faces more daytime than the southern hemisphere, which means the northern hemisphere will experience the summer season and the southern hemisphere will experience the winter season. This season happens from June to August.
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Summer in the Northern hemisphere and Winter in the Southern hemisphere |
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Summer in the Northern hemisphere and Winter in the Southern hemisphere |
Again as the earth continues to revolve around the sun, it ends up leaving the autumn in the northern hemisphere and spring in the southern hemisphere. This season will take place from September to November. Again the earth revolves, and the cycle continues.
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Autumn in the Northern hemisphere and Spring in the Southern hemisphere |
During the revolution period around the sun, the earth also encounters situations like solstice and equinox. A solstice is an effect on a day, causing it to last for long or less than the normal day we experience. As we experience now, a day consists of morning and night on an average duration of 12-hour. But during a solstice, either the day becomes longer or the night becomes longer. Also, this effect can be seen only at the poles, and the area nearer to the poles. There are generally two different solstices, which are named as summer solstice and winter solstice. In summer solstice, the days are longer (midnight sun) and in the winter solstice, the nights are longer. When the northern pole experience the summer solstice the southern pole experience the winter solstice and vice versa.
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Summer Solstice in Northern Hemisphere |
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Winter Solstice in Northern Hemisphere |
This solstice is mainly caused by the inclined rotation of the earth. Due to this inclined rotation, the poles of the earth will be also at a dramatic inclined position. So during rotation, either of the poles will be at one side of the earth as shown in the below figure. The solstice occurs on two major days of the year. So in the north pole, the summer solstice will occur on June 21st or 22nd and the winter solstice will occur on December 21stor 22nd, and vice versa on the South Pole.
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Summer Solstice in Northern Hemisphere
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As when you observe, during the spring season all the living things will come back to life after the long winter. In the spring season, the ices melt, the flowers blossom, rains, insects, and animals come back to life after hibernation. Meanwhile, in the autumn season, things will get opposite in the southern hemisphere. All the living things will get ready for hibernation, all the trees will drop their leaves off, and the climate gets colder. This is because the next season, the southern hemisphere is going to experience is winter, where the days get shorter, ice and snow forms, and all the living things go for a long hibernation. Meanwhile in the northern hemisphere the next season it is going to experience is the summer where the trees become green and the warm breeze begins. That is why during an equinox, even though the earth faces sunlight equally on both hemispheres, it categories itself as spring and autumn with consideration to the next season it is going to experience.
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Equinox |
One more thing that needs to be considered in the seasons is daylight saving time. A daylight saving time (DST) is the type of time that is saved during the daytime persists. Particularly at the poles, there will be a time, where the daytime gets delayed during the spring and summer seasons. During this time the sun will rise late in the morning and set late in the evening. Actually, the duration of the solar time over the day does not change dramatically. The DST only shifts the solar time to forward by an hour but the length of the day does not change unless there is a seasonal change. For this purpose, some countries will forward their clock to one hour ahead to use the daylight better. While in the fall (autumn), the clock again falls back to its standard time by keeping one hour behind, as the mean solar time shifts back to normal time. This is called daylight saving time. Many countries do not observe DST as they are present apart from the poles. Even the countries that are near to the poles do not follow Daylight saving time if they are using the GMT time zone. But those countries will change into another time zone and then will follow the Daylight saving time. For example, the British, who follow the Daylight saving time, will change into British Standard Time while following the DST. Because GMT or UTC is a standard time reference for all countries in the world. All other countries in the world set their time with reference to the GMT or UTC only. So changing the standard time zone for a particular period corresponding to DST will make complications all around the world. To know more about the time zones please visit my previous post through the link given below,
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Credit (Daylight Saving Time): Image by Mike Licht from flickr.com |
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