Prime Meridian

From Newton’s clockwork universe through to Einstein’s relativistic effects of time dilation, classic science fiction movies like 12 Monkeys, Terminator and Inception, through to the deep philosophical questions of Plato and Aristotle – the human race has an inherent fascination with time. 

(I once set a Physics assignment that had students watch the movie 12 Monkeys, and then using the film as a stimulus, answer a question that deals with destiny, time and fate – an authentic way to have students discussing the philosophy of time, time travel, debating their own thought experiments, classical v modern physics, implications etc. Students actually wanted to spend every second of their time researching and discussing mind-blowing questions like “Is the present actually the past?” Seriously, think about that one…)

More simply though, ask your students “Why do different parts of the world have different times?” and you will get a variety of answers. In fact, ask many adults the same question and expect to get the same wide variety of responses.

The Royal Observatory in Greenwich is the home of Greenwich Mean Time (GMT) and the Prime Meridian. A meridian is a north-south line selected as the zero reference line for astronomical observations. The line in Greenwich represents the Prime Meridian of the World – a longitude of 0 degrees. Every place on Earth is measured in terms of its distance east or west from this line. 


Before 1851, when this absolute reference point was first established, almost every town in the world kept it’s own local time. There were no national or international conventions which set how time should be measured. However, with the vast expansion of the railway and communications networks during the 1850’s, the worldwide need for an international time standard became imperative.

The world’s time zones are based on the fact that the Earth moves through 15 degrees of longitude each hour. Therefore, there are 24 standard time zones (24 hours x 15 degrees = 360). Time zones are counted from the Prime Meridian, with each time zone based on a central meridian, counted at 15 degree intervals from the Prime Meridian, and extends 7.5 degrees to either side of the central meridian. For example, New York City lies in the zone of the 75 degrees west meridian, and that time zone includes all locations between 67.5 degrees west and 82.5 degrees west.

(Since time zones are based on segments of longitude and lines of longitude narrow at the poles, scientists working at the North and South Poles simply use UTC time.)

Using Google Earth, and generating random locations, have students note latitude/longitude of destinations and work out the time in that location. You could also have them investigate physical features of locations and have them answer questions that involve estimation: eg. If one of the locations was Egypt – How far is it from Burundi to the mouth of the Nile?  

Have students turn on the latitude/longitude lines in Google Earth (View -> Grid), then from their current location count the number of longitude lines between them and the Prime Meridian. Then they will have to determine if they are east or west of the meridian. If they are west of the Prime Meridian, GMT will be ahead of, or minus, the time at the Prime Meridian. If they are east, the time will be after, or plus, GMT. For example, Melbourne is located 145 degrees east of the Prime Meridian, so Melbourne time is GMT+10 (not taking into account daylight savings)

(Before running this type of activity using Google Earth, it would be worthwhile reading Why Google Earth and the Prime Meridian Don’t Line Up)

The idea of time zones, latitude and longitude is an important one in a world increasingly reliant on GPS. It is not enough for students to use new gadgets or tools, but rather they need to have a certain level of understanding of how these new gadgets or tools actually operate. 

What do people think – Is it important for students to know about time zones when they can quite easily use the web to find the time anywhere in the world in an instant?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: