Chapter Notes and Summary
Rotation
• Rotation is movement of Earth on its axis.
• axis of Earth which is an imaginary line, makes an angle of 66½° with its orbital plane.
• portion facing Sun experiences day, while other half away from Sun experiences night.
• circle that divides day from night on globe is called circle of illumination.
• Earth takes about 24 hrs to complete one rotation around its axis, it is known as earthday.
Revolution
• movement of Earth around Sun in a fixed path or orbit is called revolution.
• Earth takes 365¼ days to revolve around Sun.
• Every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year.
• Earth is going around Sun in an elliptical-orbit
• Seasons change due to change in position of Earth around Sun.
• Summer solstice is position of Earth when Northern Hemisphere has longest day and shortest night. It occurs on 21st June. In Southern Hemisphere, it is winter season at this time. days are short and nights are long.
• Winter Solstice is position of earth when Southern Hemisphere has long days and shorter nights. In Northern Hemisphere days are short and nights are long. It occurs on 22nd December.
• On 21st March and September 23rd, direct rays of sun fall on equator and whole earth experiences equal days and equal nights. This is called an equinox.