Tag: geography

The summer solstice in the northern hemisphere occurs when the Sun is directly overhead at noon on the Tropic of Cancer. The summer solstice happens on 21 June. This day has the longest daylight time.

• In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane.
  
• It differs from orbital inclination. 
  
• At an obliquity of zero, the two axes point in the same direction; i.e., the rotational axis is perpendicular to the orbital plane. 
  
• Earth's axis remains tilted in the same direction with reference to the background stars throughout a year .
  
• Like Earth, all of the rocky planets have a small precessional rotation of their spin axis.
  
• A rotation is a circular movement of an object around a center (or point) of rotation .
•  A three-dimensional object always rotates around an imaginary line called a rotation axis.
•  If the axis passes through the body's center of mass, the body is said to rotate upon itself, or spin.
  
• The speed of rotation is given by the angular frequency  (rad/s) or frequency  ( turn/s, turns per minute), or period (seconds, days, etc.).
  

• The Earth experiences days and nights as a result of the planet spinning on its axis.
• As the planet spins, the part that is facing the sun experiences day, while it is a night for the part facing away from the sun.
• The alternation between day and night is caused by the rotation of the Earth on its axis.
• If the Earth did not rotate as it does, the day/night cycle would be very different or possibly even nonexistent. 

• The winter solstice falls on 22nd December during which there is continuous daylight on the South pole and continuous darkness at the North pole. Hence option D is correct.
• During summer solstice i.e. 21st June, there is continuous daylight at the North pole.
• Equinox refers to an equal period of darkness and daylight.

After 22nd March, other parallels between the equator and the Tropic of Cancer in the northern hemisphere start receiving perpendicular rays sequentially. Only on 21st June and 22nd December the sunrays become perpendicular on the Tropic of Cancer and Tropic of Capricorn respectively.These two days are called Solstice days.

Sunrays are never perpendicular to any of the parallels between Tropic of Cancer and the North Pole or between Tropic of Capricorn and the South Pole. 22nd December marks the longest day and the shortest night in the southern hemisphere.

The movement of the sun towards the north or south in a year is called the apparent movement of the sun. The revolution of the earth around the sun and the tilted axis of the earth are the two factors responsible for the apparent movement of the sun. Seasons occur only with reference to the northern and the southern hemispheres.

In the northern hemisphere , 21st March is called spring or vernal equinox whereas 23rd September is called autumnal equinox. The equinox or solstice dates can vary by a day or so.