'Fall Back': It's Daylight Savings Time ;-)

[redfalconf35]

I can't understand why anyone is really opposed to Daylight Savings Time. It takes about one day at either end to adjust. No big deal; it's just more pleasant having sunny evenings in the summer.

Because it's annoying to have to change the clocks, it screws up the toddler's schedule, it makes for a jarring change in the fall when it goes from getting dark at 6pm to the next day getting dark at 5pm, and it could be just as easily accomplished by establishing summer and winter hours at most places of business. Growing up in Indiana, we didn't do daylight savings, and the only thing that was confusing was figuring out what time it was in other states. DST is a relic of the days when there was a rigid work day that kept you locked in a windowless cubicle or factory until you could punch out. These days, it's a solution in search of a problem.

If they want to move to daylight savings time and just leave it there, I'd not object. I don't really care when the sun comes up or goes down, as long as I don't have to go through the rigmarole of resetting the clocks and my circadian rhythms every 6 months.

*goes off to grumble more about DST*

 

[shavefan]

Getting dark (almost complete) at 5pm doesn't seem like extra daylight in the evening hours to me.

I agree. I was out working in the garden this evening and losing almost all light at 5pm-ish.

 

[shavefan]

I can't understand why anyone is really opposed to Daylight Savings Time. It takes about one day at either end to adjust. No big deal; it's just more pleasant having sunny evenings in the summer.

Because I like pleasant evenings year round

Really though, what purpose is served by DST in modern times?

 

[Traveling Man]

Having usable daylight to between 8-9 p.m. for the majority of the year.

 

[Rhody]

Having usable daylight to between 8-9 p.m. for the majority of the year.

8-9 pm...how many months?
I guess im wondering how you define majority of the year

 

[Raissermesser]

Because I'm a jerk and had the time:

I set up a spreadsheet with the 2018 sunrises and sunsets for the geographical center of the continental United States. That's 39° 50' North and 98° 35' West. I then added an hour to each from March 11, 2018 to November 3, 2018. I then made a column with a 1 for every sunset equal to or greater than 20 (8 PM). Then I totaled the column.

There were 156 sunsets at or greater than 8 PM Central Time. There are 365 days in 2018. That means sunset occurs at the geographical center of the continental US 42.73% of the year with Daylight Savings Time.

 

[Raissermesser]

Because I'm a jerk and had the time, Part II:

I did the same for the southernmost point of dry land in the continental US - 24° 31' 15" North and 81° 57' 49" West. On DST, there are 104 sunsets greater than or equal to 8 PM Eastern Time. That's 28.49% of the year.

 

[Stainless Razor]

Well California voted to star the process of going on permanent daylight savings times, I would have preferred staying on non daylight saving time, but whatever, it's better than switching between the two.

 

[Traveling Man]

I don't need spreadsheets and star charts. All I know is a few weeks ago, it was light after 8 p.m. Today, it was stone cold dark as night at 5:45 p.m. That sucks.

 

[Rhody]

Thats a wide swing.

 

[Raissermesser]

I don't need spreadsheets and star charts. All I know is a few weeks ago, it was light after 8 p.m. Today, it was stone cold dark as night at 5:45 p.m. That sucks.

Then don't - and know that while sun rise and set is astronomical data, it doesn't come from star charts. That said, there's a difference between preferring DST and making an assumption about it. You like DST? Fine. It's still good to look into actual effects, and see if what we think happens actually does.. And now I have the itch to look at two more data points for the continental US.

 

[Raissermesser]

Because I’m a Jerk and had the time, Part III

Actually, I didn't have the time today, and this is on break.

I looked up three data points instead of two, when it hit me that this doesn’t illustrate the effect of DST based on latitude and longitude. The higher the latitude, the greater the difference between daylight and night in the summer and winter. Theoretically, time zones are 1 hour wide, so sunset at the eastern edge will be an hour before sunset at the western edge. Theoretically, the center of each time zone is zone x 15°. That would put the US Eastern Time Zone center at 75° West, with the theoretical eastern and western boundaries at 67° 30’ West and 82° 30” West.

I looked up sunrise and sunset for 75° West for longitudes 20°, 30°, 40°, and 50° North. I then subtracted and added half an hour to get the times for the eastern and western edge of the zone. This is what I ended up with:

Percentage of Year with Sunset Greater or Equal to 8 PM
75° Lon. 67° 30’ Lon. 82° 30’ Lon.
Lat. Stan. DST Stan. DST Stan. DST
20° 0.00% 0.00% 0.00% 0.00% 0.00% 24.38%
30° 0.00% 12.33% 0.00% 0.00% 0.00% 35.34%
40° 0.00% 27.12% 0.00% 7.95% 7.95% 40.85%
50° 13.42% 35.07% 0.00% 25.21% 25.21% 44.11%

My point? The effect of DST depends not only on latitude, but the longitude in the time zone. At lower latitudes, you just aren’t going to get as many sunsets on or after 8:00 PM as you do in upper latitudes, and the western part of a time zone will have more than the eastern.

Addendum:

So much for my nice, neat, columns.

 

[Raissermesser]

Thats a wide swing.

Theoretically possible in the upper latitudes of the continental US and the western edge of a time zone. From maybe somewhere around the end of August to now.

 

[TexLaw]

Theoretically possible in the upper latitudes of the continental US and the western edge of a time zone. From maybe somewhere around the end of August to now.

Not where Traveling Man is. Spreadsheet play is fine, but records are better.

Sunrise and sunset times in Knoxville

 

[Alacrity59]

Always more traffic accidents when the time changes. Maybe time to drop the concept.

 

[Rhody]

Not where Traveling Man is. Spreadsheet play is fine, but records are better.

Sunrise and sunset times in Knoxville

june and july have the closest sunsets to 9 pm but not actually hitting 9pm
November shows the sunset earlier noting the time change.

 

[Raissermesser]

Not where Traveling Man is. Spreadsheet play is fine, but records are better.

Sunrise and sunset times in Knoxville

The data came from the US Naval Observatory at Sun or Moon Rise/Set Table for One Year . What makes it convenient is that you can save the generated table of sunrise and sunset as a text file in your browser, and open it in a spreadsheet, selecting fixed width. From there, I set Sunrise and Sunset up in their own columns so that I had sequential data for the entire year. It's simple to convert it to decimal hours in another column, which makes it handy to add and subtract a half hour (adding a full hour is trivial, and doesn't require conversion to decimal hours). From there, it's just a matter of using the if function to put a 1 in a column for every sunset that meets the conditions, and sum them for the year and divide by 365.

As a rule of thumb, civil twilight is about half an hour before sunrise and after sunset, and we can go by that. Or we can go back to the US Naval Observatory site and calculate actual twilight. What we call dark may be the beginning or end of nautical twilight, though really dark is astronomical twilight. You can calculate all three - civil, nautical, and astronomical - at the US Naval Observatory site.

 

[Raissermesser]

june and july have the closest sunsets to 9 pm but not actually hitting 9pm
November shows the sunset earlier noting the time change.

Sunset with DST was at 8 PM in the first week of September, and was about 5:37 today, courtesy of the US Naval Observatory data. Without calculating actual civil twilight, that should be dark around 8:30 the first week in September, and a little after 6:00 now. It should have been dark at 8:00 pm around September 24, but it still should be dark now about 6:00.