Why is it the first day of fall?

Answer 1

We have seasons because of the way the earth's position relates to the sun as the earth goes around the sun. Going around once equals one year.

The amount of daylight versus darkness changes over the course of the year, and that is how we divide the seasons.

* There's a shortest day (meaning most darkness, least daylight), and that is the first day of winter. It comes about Dec. 21st in the northern hemisphere. * There's a longest day, and that's the first day of summer, about June 21st. Notice that this is six months off the shortest day--halfway around the year, halfway through one revolution around the sun. * In between going from short to long and from long to short, there's a midpoint when the day and night are the same length. That's the marker for the first day of spring (March 21st) and the first day of autumn (September 21st). Those dates are halfway between winter and summer. That makes four quarters, four seasons.

The calendar does not precisely match the movement of the planet. It varies by less than a day, but the variances add up, and that's why we have leap years, to make a correction of the variance. Because of those slight differences, the start of the season might be a day off either way, so this time (2008) the first day of fall is the 22nd instead of the 21st.

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Answer 2

The first day of fall means that the climate is cooling down and the earth is turning so that it is facing a colder part of the solar system, away from the sun.

The first day of fall is important because it is when the earth is balanced; fall (autumn) begins at the moment of the autumnal equinox. Night time begins to get longer, by several minutes at the time of the winter solstice. Daylight periods are getting shorter, and the temperatures drop.

Because the autumnal equinox happens in one instant for the whole planet, it will happen at odd times of the day each year. You may hear people refer to 'the first full day of autumn', or 'the first full day of spring'. They mean that the moment of the equinox happened some time during the day before.

Answer 3

The first day of Fall is also called the Autumnal Equinox. That is the day when there is 12 hours of daylight and 12 hours of night.

Further the Vernal Equinox is also 12 and 12 and is the first day of Spring.

The first day of Summer is the one with the most daylight hours and the 1st day Winter is the one with the least daylight. (These are referred to as the Summer Solstice and Winter Solstice)

They vary a little from year to year but typically occur as follows:

Vernal Equinox (1st day of Spring) around March 21st.
Summer Solstice (1st day of Summer) around June 22nd.
Autumnal Equinox (1st day of Fall) around September 21st
Winter Solstice (1st day of Winter) around December 22nd.
Actually, there is some pseudo-precision and lack of scientific understanding in our calling the solstices the first days of winter and summer.
The older English names for winter and summer solstice were "Midwinter" and "Midsummer" respectively. Odd, how did the middle of a season become the first day of that season?
The solstices are precisely the middle of the quarter year of least and most sun. Our ancestors, lacking any night light but fire, were much more attuned to astronomical features than we are today.
Today, we are more focused on the climate seasons than the astronomical seasons. Most people would characterize winter as the coldest season, and summer as the warmest season.
Here are two questions I ask and attempt to answer: First, what are the coldest and warmest quarters of the year? Second, how might somebody have changed the Midsummer to the first day of the summer?
First, the actual coldest quarter of the year (in the northern hemisphere) actually begins on about December 10th, and continues to about March 10th. This is pretty consistent with the characterization of the three winter months as December, January, and February. After all, if winter doesn't begin until December 21st, wouldn't December be mostly a Fall month? But we all know better than that.
Second, what is going on here and how did the change happen (from "mid" to "first")? There is a phenomenon known as "hysteresis" or "phase shift". As the northern hemisphere gets more sun, it starts to warm up. But the atmosphere, land, and ocean take time to heat up. That time lag has nothing to do with the geometrical precision of solstices and equinoxes: it is a matter of physics. There is simply no reason to expect that lag to be precisely 1/8 of a year (which it would be if the warmest quarter of the year really did begin on the summer solstice). And it isn't. By using a mathematical calculation called "regression", we've been able to model annual temperatures and average out the yearly random variations to determine that the 10th of the months December, March, June, and September really mark the transitions of the climate seasons.
So you see, when somebody says "It isn't winter yet", and you've been freezing your butt for good week, you can reply "No, Mr. Know-it-all, the coldest quarter of the year started over a week ago!"