NAV - Time

Question 1

What is Rotation of The Earth? (1)

Answer 1

Is eastward, or anti-clockwise, if viewed from
above the north pole

Question 2

How are Seasons formed? (3)

Answer 2

• Earth tilted at 23.5°
• Moves around the sun
• Global heating differential throughout the year

Question 3

What is Night (SERA)? (1)

Answer 3

‘Night’ means the hours between the end of evening civil twilight and the beginning of morning civil twilight

Question 4

What is Civil Twilight (SERA)? (1)

Answer 4

Civil twilight ends in the evening when the centre of the sun’s disc is 6 degrees below the horizon and begins in the morning when the centre of the sun’s disc is 6 degrees below the horizon

Question 5

What is Mean Solar Time? (2)

Answer 5

• Based on the motion of an imaginary Sun travelling at an even rate throughout the year
• Clocks are regulated by this imaginary sun which would pass overhead once every 24 hrs

Question 6

The Mean Sun is used to measure…. (3)

Answer 6

• Co-ordinated Universal Time
• Time Zone
• Local Time

Question 7

How is The Earth divided to give Time Zones? (1)

Answer 7

Divided in to 15° of Longitude

Examples:
Midday at 15° East longitude = 1 hour before Midday at Greenwich
Midday at 15° West longitude = 1 hour after Midday at Greenwich

Question 8

What is the IDL? (4)

Answer 8

IDL - International Date Line

• An imaginary line on Earth’s surface defining the boundary between one day and the next
• Located halfway around the world from the prime meridian (0° longitude) at 180° east (or west) of Greenwich - the reference point of time zones
• Date line varies around the 180° meridian to suit Russia, Alaska and some Pacific Islands