Time and Longitude

Question 1

What is the definition of a ‘mean solar day’?

Answer 1

The interval of two sucessive passes of the sun over a given meridian of longitude

Question 2

Why can we define one hour of time as 15°?

Answer 2

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

Question 3

What is ‘Local Mean Time’?

Answer 3

The specific time at a particular meridian. So for me when the sun is directly overhead, it is 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.

Question 4

What is UTC?

Answer 4

The time over Greenwhich, England (their local mean time). All times are measured from UTC.

Question 5

When is daylight savings time in effect?

Answer 5

SUMMER

Question 6

Why do we in Canada add hours to convert to UTC time?

Answer 6

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.

Question 7

What is fucking twilight?

Answer 7

• 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)

This is still civil twilight

Question 8

Which of the three stages of twilight does TC want you to know about?

Answer 8

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

Question 9

There is evening and morning civil twilight. When do they both begin and end?

Answer 9

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.