We're coming to the end of a new season for the twitter account @theauldsthretch, and as it now has more than 6,000 followers, it's no longer easy for me to answer individually all questions that may arise. Therefore, I'm putting together this set of questions and some short answers
Why is the earliest sunset not on the shortest day?
A detailed explanation can be found here.
The quick, bullet-point version is as follow…
- The time between the moments the sun is at the highest in the sky on any day of the year and on the next day varies throughout the year. The high-noon-to-high-noon time will sometimes be more than 24 hours and sometimes less than 24 hours.
- If we were to base the length of a day, therefore, on the high-noon-to-high-noon time, we would have variable-length days, which would be … hard.
- So, instead, we set the length of the day to a standard number of seconds and we let the time of the "solar noon" vary throughout the year. It doesn't vary all that much, so it's fine.
- This variation has a slight effect on the change in the time of the sunsets and sunrises. Considering the sunset, sometimes the variation slows the rate of the change of the sunset, sometimes it speeds it up.
- It has a similar effect on the sunrises.
- In the lead-up to the winter solstice, the solar noon gets later, and it pulls the sunsets and sunrises with it.
The result is that the sunsets turn from getting earlier to getting later before the solstice, and the sunrises turn from getting later to getting earlier after the solstice.
In Dublin, the difference is about 7-8 days either side of the solstice.
When does the Grand Auld Stretch in the evenings start?
In Dublin, it's typically the 15th December, the earliest sunset taking place on the 14th.
It depends on where you are, though. The lower the latitude (the closer to the equator), the earlier it is. The higher the latitude, the later.
Isn't the winter solstice the shortest day of the year?
Yes. It is.
Normally the solstice is on the 21st December (in the northern hemisphere), but on the years before the leap year it takes place on the 22nd December.
That the earliest sunset takes place before the solstice is balanced by the latest sunrise taking place after the solstice.
When is the latest sunset?
In Dublin, very nearly 20:59 on the 25 June. However, because daylight savings is in place, we see it as a minute to 10pm.
When is the earliest sunrise?
In Dublin, very nearly 03:55 on the 17th June. However, because daylight savings is in place, we see it as about 5-to-5am.
When is the latest sunrise?
It differs from place to place, but in Dublin it is typically about 08:39 on the 29th/30th December each year.
Some other questions I've been asked
Where do you get the times for the sunsets?
I use a python script I wrote that makes use of the Astral library. Each year, I build a database of sunset times from it.
Why don't you use timeanddate.com or <other website>?
I love coding, so I don't need to?
What are the date and time of the earliest sunset where I am?
It depends on where you are, and it would take some time for me to calculate that info; time I don't have these days (I recently got a puppy, so … no).
Where can I get more information?
I've written some blog posts here.
Why did you pick such a stupid name for your account?
I was asked this one once, and it still puzzles me that someone got so worked up about it.
I'm not going to answer it. The secret will remain with me forever.
Can you move the start of the grand auld stretch to an earlier date?
Unfortunately not. It's against the rules. I've asked.
Why does the changing of the size of the stretch slow down as we get closer to the earliest sunset?
The line on a graph that would represent the stretch is a wave, and as waves reach their peaks and troughs (or troughs and peaks, if you're holding the page upside-down), the change slows down. As we move away from the peak, the change speeds up until we get to half-way to the trough.
So. the difference between the sunset time on the day of the earliest sunset and the next day is measured in single-digit seconds, but the difference between the sunset times on one day and the next around mid-March or mid-September can be more then 2 minutes.
Can we keep the dark evenings? I love them!
I love how diverse this world can be!
(Yes, I have been asked this question!)
Ummm. It does. Occasionally.
The stretch is measured my comparing it to the time of the most recent earliest sunset (i.e. in Dublin, that's the time of the sunset on the last 14th December). Sometimes the next earliest sunset is a second or two earlier than the base one. So it can go negative.
What's with the American dates, like? Where in Europe, and you're doing it wrong!
This has been raised with me a couple of times, and it always reminds me of this joke that's very popular on twitter:
Where does a mansplainer get his water? From a well, actually.
The date format that I use in the automated tweets is
YYYY-MM-DD, which is an internationally standardised form for
dates, as outlined in the ISO-8601 specification. More precisely,
I use the extended format for expressing the dates.
This is the format I have always preferred, as it makes a
specific date much easier to find. For example, imagine sorting a
list of files that contain a date in their names. Which format do
you think is easier to work with?
As regards the time of the sunset and the length of the stretch,
I also use the extended ISO-8601 format of
HH:MM:SS for the
Anyway, the American format,
MM/DD is an abomination, but it's
not true to say that I use it in the tweets.
Questions I'd love to be asked, and am still waiting
How do you work Daylight Savings
Daylight savings is an artificial, civil construct intended to open the days up for more activity (of your choosing).
If I was to calculate the stretch to include the changes in the clock in March and October, it would feel wrong. So, while the nightly automated tweets give the sunset time with and without daylight savings, the stretch is measured as though it doesn't exist.
Which may be OK, given how it was nearly done away with in 2019.
Why "Sthretch", with that first "h", like?
It's how I would have heard is growing up, living as I did around counties Westmeath, Roscommon and Galway.
Sthretch Towers is a 3-bed mid-terrace house on the North Side of Dublin. It's a hotbed of astronomical activity.
Why do you call it a stretch when the evenings are getting shorter?
Yeah. This has caused some confusion in Sthretch Towers. The size/length of the stretch is measured against the time of the most recent earliest sunset of a year.
What code are you using for @theauldsthretch?
The code I wrote for the automated sunset tweets can be downloaded from here.
All the other tweets are manually prepared and posted.
What is @theauldsthretch anyway?!
It's a bit of fun.
Though, that wasn't the originsl point. I started it in an exasperated effort to stop (some) people from pointing out to me that there's a "… Grand Auld Stretch …" in the evenings on the day after the winter solstice. It irritated me for two reasons:
- The difference between the sunset time on the shortest day and the day after would be measured in seconds, and – typically – by the time someone finished making the observation, the sun would have set anyway!
- Many would "observe" the stretch before sunset on the day after the solstice, which always seemed ridiculous to me (as though the whole thing isn't ridiculous!), as the stretch hadn't actually taken place.
It was in a mistaken belief that I could change the world in a tiny way and correct this that I set up the account.
However, since then, I've had loads of fun with the banter through the account. That's its main purpose now.