2020: Daylight Saving Time Commentary

Astronomy, Jeffsfavs, Sky Watching
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Sunset over the ocean

In this commentary is a different idea about year-round daylight time, based on astronomical concepts for the mid-northern latitudes. Year-round or not, a different approach may yield better results.

by Jeffrey L. Hunt

From the beginning, here’s the conclusion, there’s no daylight to save during the months with the least daylight. Also note that “DST (Daylight Saving Time) is simply a work-time arrangement,” from a paper from the European Union published at the National Institutes of Health (nih.org).  We change our clocks to have more daylight during the evening hours, when there’s daylight available to shift.  The arrangement would work better if the clocks returned to year-round standard time to allow companies, schools, and families determine their own schedules.

The authors of the above study cite myths around DST, including one that shifting the clock one hour ahead creates an extra hour of daylight. Rather, it moves time one time zone eastward.  The authors conclude, that countries should consider “Obliterating DST (in favor of permanent Standard Time) and reassigning countries and regions to their actual sun-clock based time zones. Under such adjustment, social (local) clock time will match sun clock time and therefore body clock time most closely.”

Companies and other organizations can provide flexible work times or change their shifts if their employees want “longer evenings” at particular times of the year.  The authors advocate for year-round standard time.

Around the equinoxes, the popular press focuses on daylight and nighttime; this is followed by a twice-yearly rant about changing the clocks.  When I consider my notes and articles about the sky, I look farther into daylight and nighttime. I break the latter into twilight and darkness.  Twilight, after sunset or before sunrise, has three phases.  Civil Twilight occurs when the sun is 6° below the horizon. Nautical Twilight occurs when the sky is 12° below the horizon, and Astronomical Twilight occurs at the −18° mark.  When the sun is 18° below the horizon, throughout the night and until it reaches −18° altitude in the east, the sky is as dark as it gets naturally.  Statements like, “Dark as midnight,” “darkest before the dawn,” and other similar metaphors have nothing to do with the reality of darkness of the night, and they are inaccurate statements of nature’s light and dark cycles.  

I break the 24 hour cycle into daylight, twilight, and darkness – the time after evening twilight ends and morning twilight begins. Daylight and darkness are equal during late October and then again during early February.

Recently Steve Chapman penned an article  in the Chicago Tribune about the need to keep daylight time throughout the year.  The main focus was about evening driving versus morning driving. Chapman referenced a study about the subject:  Time Well Spent: An Economic Analysis of Daylight Saving Time Legislation.

The study reviews the history of the topic, an analysis of energy consumption, a discussion of effective drive times, and an analysis of daylight during January.  The final conclusion of the article is to keep daylight time during the colder months to mitigate evening driving difficulties.

 Chapman discounts claims about children safety with, “If morning darkness is perceived to pose a danger to kids in some places, schools could push back their start times an hour.”  Anybody with children in high school activities know their children already arrive home as late as 10 p.m. from practices and performances.  Adding another hour to their arrival time is not acceptable to parents, even when school starts an hour later the next morning.

The issue of daylight is not only with January, but starts earlier. By mid-October, the shortening daytime length is noticeable. I have looked at three analyses. One looks from the time of equal daylight and darkness – the time beginning at the end of evening twilight and ending at the beginning of morning twilight – that occurs during late October and recurs during early February. The winter solstice is the mid-point of the time interval.  The second looks at centering the study on the date of Earth’s perihelion (January 2).  The third considers the time around when the sun is truly in the south, at the meridian, at noon on the clock. Here’s what I found:

For the first analysis, I looked at the length of daylight from about the time of equal day – equal darkness, centering on the winter solstice about 50 days later and ending a few days after the equal daylight – equal darkness day, 50 days later, for a total time interval for 101 days, used for all three reviews.  I used sunrise, sunset, and twilight data from the U.S. Naval Observatory for Chicago, Illinois.

For this purpose, the first day is Halloween (10 hours, 24 minutes of daylight).  On the winter solstice, daylight lasts 9 hours, 8 minutes.  The interval ends on February 10, 2021 (10 hours, 25 minutes).  During that 101 days the average day length is 9 hours, 35 minutes.  Because averages “are affected by the extremes,” the median (middle) value is 9 hours, 33 minutes.  So, there’s no extreme value to affect the average, indicating that the change across the interval is slow and consistent without wild variations.  For 38 days (December 2 – January 9) daylight is less than or equal to 9 hours, 20 minutes.

In the second review, I looked at 101 days centering on the perihelion date (January 2), when Earth is closest to the sun. The average day is 9 hours, 38 minutes, while the median value is 9 hours, 29 minutes.

This might be a surprise that the sun is not precisely south every day when our clocks read noon.  Sometimes the sun reaches the south point before clock noon and sometimes later.  This is from the earth’s non-circular revolution around the sun and the planet’s 23.5° tilt.      

In the third review, the 101 days are centered on the date when the sun is precisely south at noon in Chicago, Illinois (January 14).  The average day is 9 hours, 48 minutes, while the median in 9 hours, 28 minutes.

While the mid-point days span 24 days, the average range difference is only 13 minutes, hardly any time to save.  The longer interval gives a larger indication of the daylight available during the colder months at the mid-latitudes, rather than a single month after the winter solstice.

Again, regardless of the time interval that is studied across many days with short daylight, there is no daylight to save during the cold months, when 8.5 hours of work (including a meal break) and an hour of commuting time, 30 minutes each way, are factored in.  Recall that DST is simply a work-time arrangement.

Health experts have weighed in on changing the clock.  The CDC (cdc.gov) described communication that companies should use with their employees to mitigate time change.  The National Institutes of Health (nih.gov) has a paper that describes health risks of changing the clock twice a year. Cardiac risk is documented to be higher in the spring when the clocks are advanced an hour.  Further, this is elevated for individuals who sleep less than 6 hours each night. The article’s authors further note that cardiac incidents could be related to the colder temperatures of March, when the time change is implemented in the US.  The authors conclude: “The following is an easy strategy: (a) move bedtime 1 hour a few days prior to the spring shift, to limit sleep deprivation effects; and (b) take care in exposing oneself to abrupt changes of temperature in the immediate post-shift days.”

The authors ask, “Could such an easy combination of sleep strategies, scarves, hats, and gloves effectively reduce the Cardiovascular effects of DST?”

Consider this conclusion in that year-round daylight time was in effect only one year, 1974.  Critics of year-round daylight time often cite the deaths of eight children as a reason to turn back the clocks in autumn.  Often public policy is driven by such dramatic events. Even private lives are guided by profound personal events that families might say that “we’re not doing that again.” 

Admittingly, it’s a challenge making the hour jump forward each spring and it has documented health effects. Time change for travel outside the home time zone has its individual consequences.  That does not prevent local or world travel, even knowing the minimal or maximum effects of jet lag.

Certainly, the recommendations of Ronnenberg, Winnebeck, and Klerman – the authors of the first study referenced – are worth considering.  Keeping standard time and allowing organizations to modify their own work calendars gives immediate and local control to those the decision affects.  Further a relook at the time zone dimensions to connect them to regional and local work and social patterns is worth a consideration.  What works in Boston is not necessarily effective in Grand Rapids.  Both are in the same time zone, but nearly an hour apart according to the sun’s travel.  The same for North Platte, Nebraska and Ogallala, Nebraska. They are about 50 miles and a time zone apart.

So, in conclusion: There’s no daylight to save during the cold months.  DST is simply a work-time arrangement.  This issue might be better resolved with a return to year-round standard time, allowing local schools, businesses, and families decide their own summertime and wintertime schedules, with the guidance of the health concerns of the CDC.  In the long-term, a national study of how time zones better fit solar time and personal time would help policy makers decide whether time zone realignment is necessary, rather than considering year-round daylight time.  Let’s just delete the idea of year-round daylight time.  We can have more daylight in the evening through year-round standard time with localities and organizations determining their own schedules.

On November 1, 2020, the clock returns to Standard Time. Let’s keep the clock there.

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