Spring Starts Sunday, But Why Has the Date Changed?

SPACE.com ^ | posted: 18 March 2005 | By Joe Rao

[Puckster]

In the years 2008 and 2012, those living in Alaska, Hawaii and the Pacific, Mountain and Central time zones will see spring begin even earlier: on March 19. And in 2016, it will start on March 19 for the entire United States.

There are a few reasons why seasonal dates can vary from year to year.

1. A year is not an even number of days and neither are the seasons. To try and achieve a value as close as possible to the exact length of the year, our Gregorian Calendar was constructed to give a close approximation to the tropical year which is the actual length of time it takes for the Earth to complete one orbit around the Sun. It eliminates leap days in century years not evenly divisible by 400, such 1700, 1800, and 2100, and millennium years that are divisible by 4,000, such as 8000 and 12000. 2. Another reason is that the Earth’s elliptical orbit is changing its orientation relative to the Sun (it skews), which causes the Earth’s axis to constantly point in a different direction, called precession. Since the seasons are defined as beginning at strict 90-degree intervals, these positional changes affect the time Earth reaches each 90-degree location in its orbit around the Sun. 3. The pull of gravity from the other planets also affects the location of the Earth in its orbit.

The current seasonal lengths for the Northern Hemisphere are:

Winter: 88.994 days

Spring: 92.758 days

Summer: 93.651 days

Autumn: 89.842 days

As you can see, the warm seasons, spring and summer, combined are 7.573 days longer than the colder seasons, fall and winter (good news for warm weather admirers).

[Puckster]

Remember the melting glaciers in Alaska?

Remember the 0.2 degrees Centigrade that the earth has warmed?

Break out the sunscreen.....it's going to be a warm summer, thanks to many things other than my own influence upon the environment.

[plangent]

The Vernal Equinox is a Solar constant. Too bad the constructed calendar of mere mortals isn't as accurate.

[Puckster]

Exactly.

Seems the news follows the areas mentioned as having an even earlier Vernal Equinox date, failing all along to connect the dots as to a possible nonhuman reason for global warming.

[TXBubba]

Thanks for this post. Our daughter's birthday is Monday. I was just telling hubby today that Spring started tomorrow and not on Monday. He was trying to tell me I was wrong. Now I can tell him why I am correct.

[tet68]

You haven't started Daylight Saving time yet?
I set my clocks ahead weeks ago!

[tet68]

You haven't started Daylight Saving time yet?
I set my clocks ahead weeks ago!

[Puckster]

Oddly enough, the exact same scenario played out in my home with my lovely wife, and, ergo, a search on the science sites produced this........it was I who was mistaken concerning the later date.

[Puckster]

I work second shift............I don't know what your talking about........haaaaaaaaaaaaaa!

[Nowhere Man]

I know when we were still under the Julian Calender in Colonial America, I think things were so skewed that spring began on March 10th or 11th. There is an interesting website, www.time.gov that goes into calendars and the like.

[Puckster]

Thanks a lot for the site.

[TXBubba]

I've always thought Spring started on the 21st. I thought it was neat that my girl would have a birthday on the first day of Spring. So now I guess that will only be in certain years.

[RadioAstronomer]

The Vernal Equinox is a Solar constant.

Nope.

The total angular momentum of the earth moon system, which is spin angular momentum plus orbital angular momentum, is constant. (The Sun plays a small part as well, which will be ignored for this discussion.) Friction of the oceans caused by tides is causing the Earth to slow down a tiny bit each year. This is approximately two milliseconds per century, and amazingly this causes the moon to recede by about 4 centimeters per year. As the Earth slows down, the Moon must recede (this is an increase in orbital momentum) to keep the total angular momentum a constant. In other words as the spin angular momentum of the earth decreases, the lunar orbital angular momentum must increase. Here is an interesting side note: the velocity of the moon will slow down as the orbit increases.

[Puckster]

I stand corrected.....I see what you're saying.

"(The Sun plays a small part as well, which will be ignored for this discussion.)"

What say yea concerning the sunspot activity in the last 40 years. This, plus the afore mentioned article, imply that there are forces larger than mankind's total affect upon the earth.

Yes, keep the air and water clean, that's a no-brainer, however, this implies that the earth isn't quite so delicate.

[RadioAstronomer]

What say yea concerning the sunspot activity in the last 40 years. This, plus the afore mentioned article, imply that there are forces larger than mankind's total affect upon the earth.

I agree completely that the Sun has a huge affect on the Earth. :-)

I personally do not buy into the global warming scare. No more than I buy into banning CFCs due to the discovery of an ozone hole.

[Puckster]

"discovery of an ozone hole."

Speaking of which......I remember an article concerning the majority of snow cover that melts and reconstitutes into snow again seasonally, in the arctic, that had an adverse chemical affect upon ozone. Couple this with and increased length of days in Alaska and that general region.....it seems that there is a connection.

[exit82]

Ya better break out the sunscreen--I just passed gas--bigtime---and edged the the planetary average temperature upward!

[Puckster]

Yes, indeed, You-thane, Me-thane, We-all-thane...........however, speaking of methane, have you seen the data on Mars? Methane needs constant replenishment, from an organic source or consistent volcanism, to exist, and it exists on Mars.

[Puckster]

Sea salt seasons chemical brew that destroys Arctic ozone

January 18, 2001-Purdue University WEST LAFAYETTE, Ind. – Sunlight, snow and sea salt are sometimes used to illustrate nature at its best. But new scientific evidence shows that, when combined, these forces provide a potent mixture for destroying ozone.

Purdue University researchers, working with scientists from Battelle and the University of California, Irvine, discovered that bromine and chlorine, two chemicals found in sea salt, may initiate a series of chemical events that destroy ozone in the Arctic troposphere, the lowest part of the atmosphere.

The findings, published in the Jan. 19 issue of the scientific journal Science, describe the role that bromine and chlorine play in a complex series of chemical reactions that occur each spring when, after several months of darkness, sunlight interacts with the snow in the Arctic region.

The study traces the source of those chemical precursors to the salty minerals found in sea water that is carried into the snow-pack in the form of tiny salt particles by wind and waves.

"Bromine and chlorine have long been suspected as major players in this series of chemical events, but until now the source of these chemicals was unknown," says Paul Shepson, professor of atmospheric chemistry at Purdue. "Our findings indicate that this near-surface ozone depletion in the Arctic is a naturally occurring event."

Ozone, a beneficial component of the earth's upper atmosphere, is a pollutant at the ground level but is essential to the health of the atmosphere, Shepson says.

The findings may help scientists develop better models to simulate and predict longterm changes in the composition of the earth's atmosphere, he says. "Because three-quarters of the earth's surface is covered by ocean, we've uncovered a process we need to understand much better in terms of our ability to model ozone in the atmosphere."

[Puckster]

Okay....put a fork in me, I'm done for the night........sleep tight.

[RandyRep]

I have never seen the different lengths of the seasons before. Of course, those were for the Northern Hemisphere.

One reason for the difference is that the orbit of the Earth around the sun is not perfectly round - it's elliptical. And the Earth is closer to the Sun during our winter. So autumn and winter are shorter than spring and summer.

Another reason that the dates change for the start of the seasons is that the "correction factor" of "leap days" is applied every four years, and was in 2004. After a leap year, the seasons start a day or so earlier than the year just before a leap year.