Seasons

SEASONS Seasons are periods into which the year can be divided as a result of the climatic conditions, largely due to changes in the duration and intensity of solar radiation. Seasonal changes are caused by the inclination of earth's axis to the ecliptic plane and because the axis constantly points towards the Pole Star. Thus, in June, the North Pole of the axis is tilted towards the sun so that solar radiation
is concentrated in the northern hemisphere (summer sea­son) and in December, the position is reversed (winter season). It is notable that all parts of the earth's surface, excepting the equatorial latitudes, experience a defiJUte rise in temperature during the rest of the year. During the four seasons-summer, autumn, winter and spring-the posi­tion of earth vis-a-vis the sun changes as it revolves. The
overhead position of the sun changes, resulting in summer season in the northern hemisphere between March 21 and September 23, while it has the winter season between September 23 and March 21, and vice-versa in the southern hemisphere. Spring and autumn are shorter seasons, marking the transition between the two main seasons. While these four seasons are the pattern in mid-latitudes, the tropical pattern is commonly a wet season (in which the sun is overhead) and a dry season. In South Asia these become summer monsoon and winter monsoon.

SOLSTICE Solstice is one of the two dates in the year on which the sun reaches its greatest altitude north or south of the equator and is directly overhead along one of the lines of the tropics.

Summer Solstice On June 21 or 22, the earth is so located in its orbit that the sun is overhead on the Tropic of Cancer (231hoN). The northern hemisphere is tipped towards the sun, having the longest day, while the southern hemisphere i$ tipped away from the sun, having the shortest day. The sun rises north of east and sets north of west.

Winter Solstice On December 21 or 22, the earth is in an equivalent position on the opposite point in its orbit; so the southern hemisphere is tipped towards the sun and the northern hemisphere away from it. The sun is overhead on the Tropic of Capricorn (231hOS), resulting in the shortest day in the northern hemisphere. The sun rises south of east and sets south of west. (However, in this context, 'winter' applies only to northern hemisphere; southern hemisphere experiences summer.)