How fast the days are getting longer (2023)

Living among Muslim and Catholic people in a time of simultaneous Lent and Ramadan, I first read "How the Fast Days are getting longer" and thought "How true, how true".

An interesting thing that non-muslims may not consider is that because Ramadan goes backwards in the western calendar approx. 10 days per year, for many people it'll be only a few times in their total lifespan when they experience and remember it being in the middle of summer and also in the middle of winter.

So you have to plan your daily routine around the rules of Ramadan, and their interpretation differ by your location and from year to year?

It's fascinating how religious practices, like fasting from dawn to sunset, can make astronomical events feel so much more immediate and personal

I am heading to the local cafe right now. This is the only time of the year they make Special Ramadan Phirni and they don't even share that exact recipe. I have begged them many times: either make it year round or for just give me the bloody recipe.

Having grown up around the same latitude as Stockholm, one thing I never realized until last year when visiting tropics is how my subconscious associates warmth with long evenings. Being used to summers where you could basically read a book outside at 11PM, it felt really weird to be outside in tropic heat, but complete darkness by 6PM.

Similar experience for me but probably even more extreme.

I'm originally from São Paulo, Brazil, the Tropic of Capricorn almost cuts through the city itself. Sunrises and sunsets are very quick events, sitting somewhere to watch it would take some 30 minutes, and then darkness.

Even after 10+ years of living in Sweden I still get mesmerised by sunrises and sunsets here, they last for so long and I get to be awed by the changing of colours, shadows, shapes, for hours. It's one of my favourite things to do during summers, just to be out somewhere by a lake with some friends, having food and drinks, and watching the endless twilight.

> When living in Stockholm, I came to appreciate the various levels of twilight and darkness, rather than thinking of day and night so strictly.

In Chile you get somewhat long days and short days too, especially in the south, but instead of trying to be super precise about sunlight, the afternoon and night blend in and sort of crossfade. You end up with "8 de la tarde" (8 in the afternoon), and "6 de la noche" (6 at night) depending on the season.

Australia spans, what, 40 odd degrees of latitude.

Where I’m at in Aus it’s day light till 10pm at the summer solstice.

No sun to really speak of at the winter solstice though.

Growing up in Australia, you must have experienced quite a dramatic shift in how daylight feels when you moved

Depends. I lived in St Kilda where the beach faces east. The sunset / golden hour seem to start from 6pm to 9pm.

Funny because growing up in the tropics I thought sunset and sunrise were synonymous with those times of the day, and learning people in other parts of the world experienced shrinking/lengthening day/night cycles was mind blowing. You mean it's 8PM in the night but the sun's still in the sky?

  > The whole "6am sunrise and 6pm sunset every day of the year" thing at the equator is kind of mind blowing.

Essentially in these regions, there are no real seasons. At least in the sense that many think of them. Things do change, but winter isn't that different than summer.

I know there are variances, but the scale masks a bit of what's going on. So let's look at London[5], Osaka[6], Auckland[7], Los Angeles[8] (often joked at for having no weather), Seattle[9], and Oslo[10]. As you can see, these are extremely different situations. It even has large effects on how people think about weather, time, and other things.

It's funny how what is so obvious and normal to some are completely different to others. Sometimes seeming as if we live in different worlds. In some sense, we do, and I think we often forget that.

  [0] https://www.timeanddate.com/weather/kenya/nairobi/climate
  [1] https://www.timeanddate.com/weather/gabon/libreville/climate
  [2] https://www.timeanddate.com/weather/brazil/macapa/climate
  [3] https://www.timeanddate.com/weather/ecuador/quito/climate
  [4] https://www.timeanddate.com/weather/malaysia/kuching/climate
  [5] https://www.timeanddate.com/weather/uk/london/climate
  [6] https://www.timeanddate.com/weather/japan/osaka/climate
  [7] https://www.timeanddate.com/weather/new-zealand/auckland/climate
  [8] https://www.timeanddate.com/weather/usa/los-angeles/climate
  [9] https://www.timeanddate.com/weather/usa/seattle/climate
  [10] https://www.timeanddate.com/weather/norway/oslo/climate

There is the same number of hours of daylight, but near the poles you sleep through a lot of those hours in summer. So you experience far fewer hours of daylight.

Another mind blowing thing about the equatorial sun is seeing it above you! Where I grew up, the sun is never higher that 30 degrees.

I lived in East Africa for a while and you’d get kick out of the way time is referred to in Swahili, “midnight” is 6am, and the first hour of the day 7am etc. makes a ton of sense when sunrise is around the same time each day!

Yes, though a location at 45 degrees N/S only gets 70.7% as much sun power per area due to not being perpendicular to the sun's light, and even less on the ground due to extra atmosphere to pass through.

> Another maybe counterintuitive fact is that (to a reasonable approximation) everywhere on earth gets the same number of hours of daylight over the course of a year.

Not the same amount of usable daylight though as the amount you have to waste to get a decent amount of sleep all year around varies by latitiude.

Living at the equator most of my life, it's actually funny how schedules are messed up when the sunrise is half an hour earlier or later. Traffic becomes chaotic because some people insist on getting home before sundown, or things like people becoming uneasy that the school starts before sunrise.

Weather is fun too, because it changes by +/- 3 degrees throughout the year. The heat makes my bedroom door expand. We had an argument with the housing developers because we had custom doors that didn't fit. But turns out it was passing all the tests when they ran it, and not in hotter periods of the year.

When we were in Hawaii I think the only reason we caught the sunset is because we were less than 400 yards from a beach. By the time you know the sun is going down you are about to be in the dark.

Movies about vampires in the Arctic Circle are fun but vampires at the equator would be more terrifying for the humans at dusk and for the vampires at dawn.

Restated in mathier language: sin(30 degrees) = 1/2 and sin(60 degrees) isn't that far from 5/6.

That was a fascinatingly good approximation of sin().

Not quite a straight line, but definitely a dramatic change (toggle the "Day/Night Length" view to see what I mean): https://www.timeanddate.com/sun/norway/longyearbyen

That's called "twilight". In the section "Atmospheric refraction and the solar limb" there's a modified sunrise equation with a variable "a" and text suggesting a correction of 50 minutes of arc there.

If you replace 50 minutes with: - 6 degrees, you get the times of "civil twilight" (roughly speaking, when you don't need light outside). At 60 degrees north at midsummer the minimum altitude of the sun will be about -6.5 degrees so almost all of the nominal night is civil twilight. - 12 degrees is "nautical twilight" (horizon clearly visible) - 18 degrees is "astronomical twilight" (sky is dark enough for all astronomical observations).

(It's possible that those are defined as 6 degrees + 50 minutes, etc.)

And it's not just "sunset + X minutes" where X would be a constant. In the winter this X is much shorter than in the summer.

For me X is then a "travelling" value which in the winter is at 1/3 between sunset (0°) and civil dusk (-6°), and in the summer it goes up to 2/3. Calculated as the moment when the blinds go down.

I'm using https://astral.readthedocs.io for this.

Twilight is caused by scattering rather than refraction. There's sunlight bouncing around in the atmosphere, keeping the sky non-black even after sunset.

I just pulled up Whitehorse, Yukon (at the 60th parallel), and sure enough, the longest day of the year is essentially always day: https://www.timeanddate.com/sun/canada/whitehorse. Almost 5 hours of civil twilight, but civil twilight is still daytime in my book.

Even in the UK around 51-52°N you get a few nights around midsummer where it never truly gets dark - no darker than ‘nautical twilight’ at least.

Even during the "night," the sky stays illuminated enough that it never truly feels dark. It definitely challenges the idea of what nighttime means and makes the summer feel almost magical, but I imagine it can also mess with your sleep patterns!

I think the section “Atmospheric refraction and the solar limb” near the end of the article addresses this.

What do you guys think about the movie Insomnia with Al Pacino and Robin Williams?

I guess you have a lot of time to philosophize about the sun when you're knocking back your sixth cup of coffee for the day.

You should live in London! UTC, time zone and solar time all close to each other :) Now if we got rid of that pesky DST...