The astronomical calendar determines the seasons due to the Both equinoxes and solstices are related to the Earth's orbit around the Sun. Meteorological seasons are derived by splitting the year into four periods made up of three months each. These seasons are split to coincide with our Gregorian calendar, making it easier for meteorological observing and forecasting to compare seasonal and monthly statistics.
By the meteorological calendar, the first day of autumn is always 1 September; ending on 30 November. Solstices and equinoxes are considered to be the astronomical transition points between the seasons and mark key stages in the astronomical cycle of the Earth. In a year there are two equinoxes spring and autumn and two solstices summer and winter. The dates of the Equinox and Solstice aren't fixed due to the Earth's elliptical orbit of the Sun.
The tilt — possibly caused by a massive object hitting Earth billions of years ago — means that for half the year, the North Pole is pointed toward the sun as in the picture below.
For the other half of the year, the South Pole gets more light. In the video, you can see how the line separating day from night called the terminator swings back and forth from the poles during the year.
You can see the dramatic change in the arc of the sun from December to June. This is a 6 month pinhole photo taken from solstice to solstice, in Medicine Hat, Alberta, Canada. We are one of the sunniest cities in Canada, and this shows it nicely.
You can easily make a similar image at home. All you need is a can, photo paper, some tape, and a pin. Instructions here. Meteorologically speaking, summer is defined as the hottest three months of the year, winter is the coldest three months, and the in - between months are spring and fall. Meteorological spring includes March, April, and May; meteorological summer includes June, July, and August; meteorological fall includes September, October, and November; and meteorological winter includes December, January, and February.
Astronomically speaking, yes, fall begins when the Southern Hemisphere begins to receive more sunlight than the Northern Hemisphere. And that starts on the autumnal equinox. But not every place will experience the exact same amount of daylight. For instance, on Monday, Fairbanks, Alaska, will see 12 hours and 14 minutes of daylight.
Key West, Florida, will see 12 hours and seven minutes. You might also notice that both of these locations have daylight times longer than 12 hours. Daylight time is slightly longer than nighttime on the equinox because of how we measure the length of a day: from the first hint of the sun peeking over the horizon in the morning to the very last glimpse of it before it falls below the horizon in the evening.
Because the sun takes some time to rise and set, it adds some extra daylight minutes. Check out TimeAndDate. The practice originated in China as a tradition on the first day of spring in the Chinese lunar calendar in early February. This is a myth. Today is the first day of Autumn or the first day of Spring for those in the southern hemisphere. This year it happens to fall on September 23, but that date can vary from the 21st to the 24th.
It all has to do with our swiftly tilting planet. So it would seem that the Autumnal Equinox should begin on the same day every year. Typically we consider days to be a year, but a solar year is actually So a typical calendar year is a bit shorter than a solar year, and leap years are a bit longer. But even if a solar year happened to be exactly days, over the centuries the marking of the seasons would still drift relative to the calendar year.
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