Posts Tagged ‘daylight hours’

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Understanding Daylight Savings Time

March 9, 2014

earthEarly this morning (2:00AM local time), we “sprang forward” and advanced our clocks one hour.  What was 2:00 in the morning suddenly became 3:00.  Daylight Savings Time is nothing more than a cleaver shift of daylight hours to better conform to when most people are up and about.  It does not create more time of light; it simply is a better use of it for most of us.

Benjamin Franklin was one of the first proponents of such a shift in time.  Back in his day, there were very practical reasons for such thinking, even if he did write somewhat satirically about it[1].  Today, its impact is debatable but does arguably make better use of the day.

Understanding just what really takes place requires a little background.  The earth has 24 time zones.  Think about it for a moment, it also explains a day being 24 hours.  Now I know a day is not exactly 24 hours but we are not trying to set an atomic clock here, gallon chemistry will do.  Humans tend to be creatures of the day, or diurnal.  If the whole of the planet used a single time zone, in London, the sunrise could be 6:00AM on a given day but sunrise would be 11:00AM in New Your City and 2:00PM in Los Angeles on that same day. For centuries, locations around the world used a local time based on the rising and setting of the sun.  As we became world travelers, thank you Ferdinand Magellan, the need to standardize time from one place to another became increasing important. 

Now for a little bit of geometry, and you told your 8th grade teacher you would never use it!  If you think of the planet as a globe, its diameter is a circle with 360°.  When people started to think about time in relation to available daylight, they figured why not make a time zone for each hour of the day.  You do that by dividing 360° by 24 hours.  This gives each time zone 15°.  Think about it this way, when the earth rotates 15° one hour has passed.  Our time zones follow lines of meridian and bisect the North and South poles.  The middle meridian of a time zone is called a standard meridian.  The boundaries of each time zone are plus and minus 7.5° from its standard meridian.  For example, New York City has a central longitude of approximately 74° West.  That puts it 5 time zones away from Greenwich, England, which is the zero reference point.   The standard meridian is 75° West.  The -5 time zone runs from 67.5° West to 82.5° West.  That puts New York City pretty close to the middle of the time zone.  When it is midnight in New York City, it is 5:00AM in London.

That is more than enough of the nerdy stuff.  The thing to remember is each time is one hour different from the time zone next to it.  When we move clocks forward, or spring ahead as they say, we are simply saying we now set our clock to -4 time zones away from Greenwich instead of -5. This has the effect of making the sunrise and set one hour later.  When we wish to end Daylight Saving Time, we simply fall back, or return to our actual time zone of -5.

If we did not take advantage of Daylight Saving Time, during the summer months, as the length of daylight increases, the sun would rise very early, like 4:00AM early. That is not much use to most of us. Daylight Savings Time is not some big conspiracy or governmental mind control trick. It simply is a way to better use available daylight. 

 


[1] Franklin, Benjamin, and Nathan G. Goodman. “Letter to the Editor of the Journal of Paris, 1784.” The Ingenious Dr. Franklin: Selected Scientific Letters. Philadelphia: Univ. of Pennsylvania Pr., 1931. 17-22. Print.

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