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Part X : The Environment

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 A day in the life of a lizard   01 hours- At night when the air is cold, the body of the lizard cools down. The lizard sleeps in its hole. 08 hours - The sun rises and during the morning the air warms up. Eventually, the sleepy lizard crawls out of its hole into the sunlight. The lizard will find a piece of rock or sandy ground which is exposed to the sun and it will lie there. In this way the lizard warms its body up above the air temperature. This is called basking. 10 hours - The lizard is quite active now, hunting for food and defending its territory. 12 hours - The temperature in full sunlight can reach 40°C or 50°C in tropical regions. This could be dangerous for the lizard; itcould become too hot. The lizard retreats to its hole to find some shade. 17 hours - The Sun's heat cools down so the lizard can come out of its hole to hunt again 21 hours - The sun goes down and night falls. Gradually the air becomes colder and the lizard returns to its hole to sleep. In this way the lizard has kept its body temperature constant right through the day. Only at night does the lizard's body become too cold to remain active.

 Over to You! How do the trees in the courtyard change over the year from season to season? Are there changes in the animals which inhabit the school's courtyard from season to season? What differences in the environment can be expected between night and day?

# THE SEASONS AND THE SUN

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## The Seasons and the Sun

The Earth is in fact tilted on its own axis. As the Earth rotates around the Sun, the northern hemisphere will be tilted slightly more towards the Sun in the summer months than in the winter months. This makes it warm in Europe in June, July, and August.

The diagram above shows the position of Paris (indicated by the Eiffel Tower) at noon at different seasons of the year. At which position (A or B) would you expect it to be colder in Paris? What do "x" and "y" represent?

At the same time of the year in the southern hemisphere, it is colder because the south pole is tilted away from the Sun. So in Australia, the months of June, July, and August are the coldest months of the year. These annual temperature changes in the different hemispheres are referred to as seasons.

At the equator, the effects of the tilt of the Earth's axis are less intense. The Sun seems to be directly overhead at all times of the year. The result is that the climate remains more or less the same throughout the year.

Each year, in the northern hemisphere there are four days with an astronomical importance:

 The first two are the days with the same amount of sunlight hours as night hours. These are, respectively, the spring equinox and the autumn equinox on or near the 21st of March and the 21st of September. The third is the day with the maximum number of hours of sunlight and the least number of night hours. This is called the summer solstice and it occurs on or near June 21st. The fourth is the day with the shortest number of hours of sunlight. This is called the winter solstice and it occurs on or near the 21st of December.

Keep in mind that the winter solstice happens when the north pole is pointing away from the Sun. At the same time, the other pole will be experiencing the longest day because it is tilted towards the Sun. The spring equinox marks the beginning of springtime and the autumn equinox marks the beginning of the fall. It should be obvious that the solstices and the equinoxes are six months apart.

 Solstices and equinoxes can be between the 20th and the 23rd of the months listed. The dates vary from year to year. To find out what the dates are this year, it is necessary to check an almanac.

Many countries have adopted a system whereby clocks are turned back an hour in autumn and set ahead an hour in the spring. This is called daylight savings and it has allowed countries to save money on electricity.

## How the Seasons Influence the Biosphere

Seasonal changes greatly influence the plants and animals living on Earth. At different times of year, the numbers and types of organism found in different places will differ greatly according to the time of the year as indeed they differ during the day time and the night time. Plants make their food during the daytime using energy from the Sun. At night, plants cannot make food.

Some animals prefer the night time to feed. Mice and other rodents feed at night so that they can hide in the dark from other animals who want to eat them. Good mice hunters like owls can fly and catch mice at night. Most birds prefer the daytime, however, and so do many animals. Many living organisms depend on the heat from the Sun to keep them warm.

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