Time and Seasons

The earth rotating on its axis and spinning around the sun creates time and the seasons. It rotates once per day (24 hours) on its axis. This gives the effect of day and night.

Our planet orbits the sun once a year, 365 days, and because it rotates at an angle of about 23.5 degrees from the vertical, we experience the seasons: Summer, Winter, Spring, and Autumn (Fall).

This then causes the variance in the length of daylight during the year.


Notice how the North Pole would experience 24 hours of daylight during the Northern Summer, conversely the South Pole would be in total darkness. The reverse applies during the Southern Summer. So depending on your Latitude, that is your distance from the Equator, will determine the length of daylight each day throughout the year.

At the Equator the sun will rise at 6:30 am and set at 6:30 pm every day. As you move away from the Equator these times change dramatically with a change of seasons, to the extremes mentioned with the poles.

The time zone in which we live is really a local time zone. The reason that we have a local time zone is because everyone likes to see the sun rise about 6:30-7 am and set 6-7 pm.

To achieve this and have a system for others to know our time zone we have to appreciate the use of World Time. World time is called either GMT or UTC. GMT is the most common name and is short for Greenwich Mean Time. Greenwich is a suburb of London U.K..... Longitude of 0 degrees passes through Greenwich.

The reason for this is historical, based on the world's first accurate time device. Until the late 1770s East-West navigation over long distances was not particularly accurate because of lack of accurate timekeeping. Latitude, ie North-South, was reasonably accurate because of the access of the sun.


Every aeroplane and ship around the world operates on World Time, GMT or UTC. The reason being that everyone is working on the same time reference.

When the plane or ship arrives at an airport/port the Captain will nominate the local time. How does he/she know how to do this?

The world spins on its axis every 24 hours. There are 360 degrees in a circle. If you divide 24 into 360 you get 15. Hence every 15 degrees of Longitude is worth one hour. The reference is 0 degrees at the Greenwich meridian of Longitude.


Every 15 degrees East of Greenwich is an hour ahead of GMT because the sun rises in the East. The opposite applies to West Longitude. Honolulu is approximately 155 degrees West, hence the local time zone is 10 hours behind GMT. Sydney, Australia, is approximately 155 degrees East, so the local time zone there is 10 hours ahead of GMT.

Many places around the world add an hour for daylight savings to make better use of the sun for up to six months. It is only necessary to know where and when this applies to calculate the local time zone.

  Professional Web Solutions and Training

Home |How a plane flies | Flying General | Watch an approach | Weather | Turbulence | Engines
Plane noises | Navigation | Intsrument Flight | Instrument approach | Holding | Delays | Exercises
Time | When things go wrong | B747-400 details | Aviation websites | FAQ | Security | Contact
©Tallships Computing Sevices 2003. All rights reserved.