social

• causes of change in seasons : 1) revolution - the earth revolves around the sun in an elliptical orbit . this motion is known as revolution
• variation in the amount of sunshine received is also a reason for occuring of seasons
• the earth's axis is tilted at an angle of 66 1/2 degree from the orbital plane and 23 1/2 degree when it is measured from the vertical plane.
• the earth maintains this tilt throughout the revolution and this is known as parralism of the earths axis
• since parralelism is maintained same throughout the revolution the position of the sun in relation to the earth varies apparently between the tropic of cancer and tropic of capricorn - apparent movement of the sun
• as a result of the apparent movement of the sun between the tropic of cancer and tropic of capricorn different seasons get repeated in a cyclic manner
• seasonal chnages are not very obvious in tropical regions because of the incidence of large amount of sun rays throughout the year
• equinoxes - equal amount of sunlight is received in the northern hemisphere and southern hemisphere when the sun is vertically over the equator . the apparent position of the sun will be vertically over the equator on march 21 and sep 23. lenth of day and night will be equal
• summer solstice - from march 21st onwards the sun apparently shifts from the equator northwards and reaches vertically above the tropic of cancer on june 21st .
• from june 21st , the southward apparent movement of the sun begins and again reaches vertically over the equator on sep 23 - summer season in NH
• winter solstice - from 23 sept the sun continues its southward apparent movement from the equator and reaches vertically above the tropic of caprticorn of dec 22
• from dec 22 onwards , the sun begins its northward apparent movement from the tropic of cancer and reaches vertically over the equator on march 21st - winter season in NH
• utharayanam - following the winter solstice , the sun sets its northward apparent movement from tcap to tcancer on 21st june .
• following the summer solstice ,m the sun sets its southward apparent movemnt from the t of cancer and it culminates on t of cap on 22 dec this
• utharayanam - following the winter solstice , the sun sets its northward apparent movement from the tropic of capricorn and it culminates on the tropic of capricorn
• equinoxes . when the sun is vertically above the equator the northern hemisphere and southern hemisphere will have equal days and equal nights .