Tag: rotation and calculation of time

Christmas is celebrated in summer in Australia because Christmas is celebrated everywhere on 25 December, and that date — in most of Australia — is in the summertime. And, for Christians at least, Christmas is fundamentally about the birth of Christ — whenever that may have occurred — and not about winter.

False

• Sun rays falling vertically move between 23 and 1/2 degrees north and 23 and 1/2 degrees south latitudes throughout the year. On 22nd december, the sun rays fall vertically at the 23 1/2 degrees south.

The axis of the Earth is tilted at an angle of 23 1/2° from a perpendicular to the orbital plane.  This tilting of the axis is called the inclination of the Earth's axis. Due to this inclination, the axis of the Earth makes an angle of 66 1/2° with the plane of the Earth's orbit.

On 21 June sun rays fall vertically over the Tropic of Cancer. This position of the Earth is called Summer Solstice. On this day, It is considered the longest daylight time in Northern Hemisphere but in Southern Hemisphere, it is considered as the shortest daylight time.

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.