Time Flashcards
What direction does the earth rotate
Eastwards
What is the apparent motion of the sun
East to west
Looking down on the sun what direction do the planets orbit
Anti-clockwise
What angle is the spin axis of earth to the plane or ecliptic
66.5°
What is declination
Angle from celestial equator
Max declination of the sun = 23.5°n/s
Celestial latitude
What is celestial longitude
Local hour angle
What is an apparent solar day
Time for the sun to appear in the same place in the sky relative to the observer
= slightly more than 1 rotation of the earth
Sidereal day
One rotation of the earth
What is the transit of the sun
Point where sun reaches highest point in the sky
Also the point the sun passes over meridian
Where in the orbit does the earth move quickest
Perihelion
When is apparent solar day the shortest
At the equinoxes
What is the max variation in time for apparent solar day
50 seconds
What is mean solar day
Average length of apparent solar day over a year
24 hours
How much does the apparent time oscillate within the mean time
+ 14 mins
-16 mins
What is the max difference in mean and apparent sun
Feb = + 15 mins Nov = -16 mins
Difference is due to wobbling about the earth axis and variable orbit speed
What is the equation of time
Mathematical relationship between mean and apparent sun
What is local mean time
Time measured by reference to the mean sun
When does a day start
At midnight which is when the sun transits the observers on the antimeridian
what is the arc to time relationship
360° = 24 hours
1 hour = 15°
4 mins = 1°
1 min = 15’
Can change local mean time at one position to another by change in longitude
Where is LMT and UTC the same
Only on the prime meridian
When does morning civil twilight begin
When centre of sun is 6° below horizon
When does evening civil twilight finish
Centre of sun 6° below horizon
How does the duration of twilight vary with longitude
Content irrespective of longitude
