5 ms·
He omitted a really big one - the beginning of spring. Most people are convinced spring begins at the equinox around 20th March but are also quite happy to talk
by cutler 5y ago
He omitted a really big one - the beginning of spring. Most people are convinced spring begins at the equinox around 20th March but are also quite happy to talk about Mid-Summer's Day at the summer solstice around 20th June. Sorry, ya can't have it both ways. If the summer solstice is mid-summer then the spring equinox 3 months earlier must be mid-spring. It all boils down to how seasons are defined and here I find even astronomers can be really lazy in their thinking. Seasons are defined by the intersection of the Sun's apparent path and the equator so equinoxes are where the Sun's path crosses the equator and the solstices (Sun standing still) are the maxima and minima of the Sun's path. However, a maxima/minima can only be the mid-point of a season since points either side of a maxima/minima are equal in terms of the relative amounts of daylight. Seasons are defined by the amount of daylight, hence the summer solstice in the northern hemisphere, around 20th June, is the mid-point of summer when we celebrate "Mid-Summer's Day". All else follows from this and spring begins around 5th February in the northern hemisphere.
- charcircuit 5y agoI thought summer started on the summer solstice. I've never heard it called "midsummer's day" Spring: March April May Summer: June July August Fall: September October Novmeber Winter: December January February
- cutler 5y agoThat's exactly the fallacy I'm referring to. Mid-Summer's day (https://en.wikipedia.org/wiki/Midsummer 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.
- charcircuit 5y ago>How do you define a season? I define it as a period of time between a equinox and a solstice.
- cutler 5y agoBut 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.
- charcircuit 5y agoI 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.
- cutler 5y agoWell 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.
- charcircuit 5y ago>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.
- cutler 5y agoSo 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.
- dahfizz 5y agoThe 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.
- cutler 5y agoNight 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.
- _vdpp 5y agoIt’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.
- nisegami 5y agoThe 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.