2. Time Flashcards
Why do we get seasons?
Due to the Earth being tilted in relation to its
orbit at 23.5°, as it moves around the sun, there
is a resultant global heating differential
throughout the year.
What is night?
Night (SERA)
‘Night’ means the hours between the end of
evening civil twilight and the beginning of
morning civil twilight.
Definition of Civil twilight ?
Civil twilight (SERA)
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.
What is mean sun?
In order to regulate our lives, we divide the world into time zones each covering 15o of longitude.
Midday at 15o East longitude will be an hour before Midday at Greenwich (360 divided by 24) (30o two hours etc.)
Midday at 15o west longitude will be an hour after Midday at Greenwich. (30o two hours etc.)
What is the IDL?
International Date Line
The IDL is an imaginary line on Earth’s surface defining the boundary between one day and the next.
The IDL is located halfway around the world from the prime meridian (0° longitude) at 180° east (or west) of Greenwich - the reference point of time zones.
In which direction does the earth rotate?
eastward (anti-clockwise) if viewed from above the N pole
How do we calculate noon?
At any point on the earth’s surface, when the Sun reaches the highest point in the sky during any given day, it is noon
The duration of the civil twilight is the time?
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.
If an aircraft crosses the 180 degree meridian flying westwards, the date is put forward a day?
A sudden change of 24hrs of time zone takes place along the 180° meridian. Travelling east becomes
yesterday, westbound is tomorrow.
Lines across a map joining points of equal variation is called?
Isogonal
