#ExcelPedroWave

This Sunday morning the solar time come back again to mark the time on our clocks.

The clocks back one hour isn't get to stop time, but if you get to live twice in one night between 2:00 a.m. and 3:00 a.m. the same or different dreams and / or nightmares and it can be "fat liar" if the millions of computers around the world don't keep their events according to a Universal Time:
UTC - Universal Time Coordinated (in Wolfram|Alpha)
GMT - Greenwich Mean Time (in Wolfram|Alpha)

As exemplified by the most used computer applications:
Wikipedia - Timezones  in Unix and Windows

This failure happens to the phones with the Android operating system and functionality of Google Calendar because that has a serious flaw in the handling of time zones that can not be included as different time zones to start and end dates of events, and because of this problem, many users of this application have been losing flights and reservations and being unable to attend events and conferences. Here are some links about this problem:

Google Calendar Forum Is a lie that Google has answered us!

PCWorld - Is Google Calendar Time-Zone Challenged?

Wikipedia - Using the native Google Calendar functionality for Android phones

Wikipedia - Google Calendar inability for time zones

Since the last Sunday of March, we enjoyed the summer time, getting up an hour early and the evenings are longer, and the last Sunday in October we come back to winter again, getting up an hour late and the evenings are shorter . In some countries the delay of clocks and watches is the first Sunday in November, as in Canada, Mexico and the United States, except Hawaii and Arizona. In Peru, Japan or India, the clocks do not change throughout the year.

These time changes for Europe are internationally known as:
Daylight Saving Time: CEST - Central European Summer Time or Savings Time (in WolframAlpha)
Winter Time: CET - Central European Time (in WolframAlpha)

For many, myself included, we would have liked the time change had been extended throughout all the year instead of only in summer, so the evenings are longer, but I fear that farmers will not agree with us and prefer to have more sunlight in the morning and, for them, summer time is a nuisance.

Whoever wants to know when is sunrise and sunset at any place or city in the world, knowing its geographic coordinates, can download the following calendar that I prepared for the occasion, in Excel without macros:

Programmable Task Calendar.xlsx

The calculation are based on Astronomical Algorithms by Jean Meeus and are posted on the NOAA page from which you can download Excel files with algorithms:

ESRL Global Monitoring Division - GRAD Group

These calculations are valid only for dates between 1901 and 2099, due to the approach used in the calculation of Julian Day.
Cities sheet contains a table with 664 Spanish cities, which can be expanded, with the latitude and longitude in decimal degrees, as in columns E and F is the conversion of degrees and minutes to decimal degrees.

In the Solar sheet, the yellow cells can be modified, where the cell A4 is the selected city. All calculations are based on the geographical coordinates of the place, for what you can enter the latitude and longitude in cells B5 and C5.

The Timezone must be entered in cell D3 as time difference from GMT.

In the case of Spain, the standard time is CET = GMT +1 (Cell D3 = 1) and there is daylight summer time (CEST = GMT +2) for what used cells D9 to D13, with corresponding dates in C9: C13 change from winter to summer and summer to winter, which is the last Sunday of March and October, respectively:

=DATE(Cal!$O$2,3,CHOOSE(WEEKDAY(DATE(Cal!$O$2,3,1)),29,28,27,26,25,31,30))

=DATE(Cal!$O$2,10,CHOOSE(WEEKDAY(DATE(Cal!$O$2,10,1)),29,28,27,26,25,31,30))

If there is no daylight summer time setting in your city, put the cells D9 to D13 to zero 0.

Remember to change the time on Sunday in Spain, at 3 am will be 2 am and this weekend I will devote that hour to change all clocks at home. What fun!