Does the Time Change Mean We Have More Daylight?

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Time changes but daylight doesn't (Photo by David O)

We reset our clocks, but the amount of daylight doesn’t alter with the time change. Photo by David O.

I was recently asked by a reader, ” Does the time change mean we have more daylight?” Unfortunately, the answer is no – the term, “Daylight Savings Time” is the cause of much misunderstanding. It’s often thought that putting the clocks forward an hour in spring and turning them back an hour in autumn actually gives us “more daylight.” In fact what it does is provide longer daylight hours in the morning (when we turn the clocks back) or in the evening (when we move the clocks forward.)

The amount of daylight reaching any point on the earth over any 24-hour period varies according to the position of the earth relative to the sun – not by government changes to the clocks. For example, on 5 November, 2011, sunrise in New York is at 0730 (7:30 AM) and sunset is at 1748 (5:48 PM.) On the 6th of November, when the clocks have been put back an hour, sunset is at 0632 (6:30 AM) and sunset set is at 1647 (4:47 PM.) However, the amount of daylight (subject to three minutes of seasonal shortening) remains the same.

Daylight is controlled by the earth's position releative to the sun (Image from NASA)

Daylight is controlled by the earth’s position relative to the sun. Image from NASA

Daylight savings time is a purely artificial construct which affects how humans choose to operate in a social and commercial context. The rationale behind the change is that if the majority of our working life is spent in daylight, then we save energy and reduce road traffic accidents. So, although we don’t produce ‘extra’ daylight, we may make better use of the daylight that we have.

Resources:

Why We Have Seasons: How Daylight Length Changes

National Geographic News. Daylight Savings Time 2009: When and Why We Fall Back. Accessed 12 October, 2011.

US Naval Observatory Astronomical Observatory. Complete Sun and Moon Data calculator. Accessed 12 October, 2011.

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© Copyright 2011 Jennifer Young, All rights Reserved. Written For: Decoded Science

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