Time and Longitude Flashcards
What is the definition of a ‘mean solar day’?
The interval of two sucessive passes of the sun over a given meridian of longitude
Why can we define one hour of time as 15°?
We can define time as the distance the sun travels across the sky.
Example:
In 24 hours, the sun travels through 360° of longitude
In 1 hour, 15° of longitude
In 1 minute, 15 minutes of longitude
In 1 second, 15 seconds of longitude
What is ‘Local Mean Time’?
The specific time at a particular meridian. So for me when the sun is directly overhead and it is high noon. But for the guy ten minutes away, its different, technically. This is why we have time zones.
So noon over Ontario is morning in BC and afternoon on the east coast
Because the earth rotate 15° every hour, it was decided that everyone in that hour/15° has their own time zone.
What is UTC?
The time over Greenwhich, England (their local mean time). All times are measured from UTC.
When is daylight savings time in effect?
SUMMER
During the winter, when standard time is in effect (daylight savings is during the summer), what are the Canadian Time Zone conversions to UTC?
East: add 5 hours
Central: add 6 hours
Mountain: add 7 hours
Pacific: add 8 hours
During the summer, with daylight savings, all these numbers are less one hour
Why do we in Canada add hours to convert to UTC time?
Places that are westward of the prime meridian are behind UTC.
If you are traveling westward from the prime meridian, you set your watch back an hour for each time zone you cross.
What is fucking twilight?
- When we can officially claim night hours
- Occures when the sun is below the horizon but it is still light outside
- There are three stages to twilight:
Civil (still light out)
Nautical (getting kinda dark)
Astronomical (get a flashlight)
Which of the three stages of twilight does TC want you to know about?
Civil, which is because the definition of night is when civil twilight ends.
Civil twilight begins when the center of the sun’s disk hits 6° below the horizon
There is evening and morning civil twilight. When do they both begin and end?
**Evening Twilight: **
* Begins at sunset when sun is still above horizon
* Ends approximately 25 min later when the sun is 6° below the horizon
Morning Twilight:
* Begins when the sun rises and hits 6° below horizon
* Ends approximately 25 minutes later at sunrise.
What are the positions of the standard meridians (time zones) in Canada and why do you need to know them?
AST (Atlantic): 60W
EST (Ontario): 75W
CST (Man, Sask): 90W
MST (Mountain): 105W
PST (BC): 120W
