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Comment by cutler | Hacker News Reader

That's exactly the fallacy I'm referring to. Mid-Summer's day (https://en.wikipedia.org/wiki/Midsummer) is a calendrical festival observed in many cultures around 24th June close to the summer solstice. How do you define a season? What single factor determines how a season is measured? It's the relative amount of daylight. The summer solstice is the longest day.

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The entire concept of a "season" is invented. Quantizing a continuous natural phenomena into descreet bits is something humans do with everything, and we nearly never do it rigorously.

When is it "night"? At what exact moment in time does it become "night"? Nobody knows, nobody cares. It's still a useful concept.

Night is clearly defined by the Sun setting over the horizon and the following rising. The Sun's passage over the meridian is the astronomical midnight.

It’s not always clear. For instance pilots can log night hours once it’s civil twilight, but there’s also nautical twilight and then astronomical twilight, all defined by the number of degrees below the horizon the sun is. What we consider “night” is pretty arbitrary.

The sun passing the horizon is affected by your vertical position. Someone in the lobby of a skyscraper has a different sunset time than someone near the top.

>How do you define a season?

I define it as a period of time between a equinox and a solstice.

But that's just a convention. You're not explaining the phenomenon which gives rise to seasons or even what a season is. If some other culture decided to define equinoxes and solstices as the middle of a season then that would be another valid convention so to get to the root of the matter one has to define what a season is all about. The astronomical essence of seasons is the amount of daylight relative to darkness.

I don't really care about what causes it. The exact start and end dates of the seasons don't really matter, nor do they need to be consistent. Each season has things associated with them like fall has leafs turning orange and falling, or snow in winter.

Well now you're defining seasons in terms of weather and we all know how reliable that is. Here in London we've had zero snow this winter so far so does that mean we haven't had a winter? There are plenty of countries, especially the ones close to the equator, who have never experienced snow and whose summers and winters are barely distinguishable in terms of temperature yet they still have a summer and a winter defined by the longest and shortest day of the year.

>Here in London we've had zero snow this winter so far so does that mean we haven't had a winter?

If it didn't get colder than fall than it would be possible to skip winter.

So seasons are defined by temperature? In the UK we sometimes have our coldest weather in March. Does that mean the seasons have shifted? And what about countries close to the equator - do they have permanent summer? Seasons have nothing to do with temperature. Global warming is set to make that even more apparent.

>So seasons are defined by temperature?

In part. I'd say it's a combination of the temperature and amount of light you get per day.

The summer solstice around 20th June will always be mid-summer in the northern hemisphere even if it's freezing cold for the 45 days before and after. It's all about daylight and darkness. Nothing else.

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