WELCOME TO FALL:

THE AUTUMNAL EQUINOX:

Tomorrow morning at 4:51 am CDT (9:51 UT) the fall equinox will arrive.You can convert this to your own time zone using the Time and Date site. The equinox is defined as the time when the Sun is directly above the Earth's equator. This usually occurs around March 20th (the Vernal Equinox) and September 22nd (the Autumnal Equinox). At this time the Sun crosses celestial equator. The equinox is also the time of year when the celestial equator intersects with the ecliptic. The equinox is a point in time, not the name of a day. The day when daylight and nighttime are "most nearly equal" is referred to as the Equilux. while the equinox falls on September 23rd this year the equilux will actually be September 26th.

The time of the equinox isn't fixed. Each year they fall about 6 hours later. This is partially corrected by the leap year every four years which resets the time of the event. The reset isn't perfect however, and there is a slow drift of the time of the equinoxes (and solstices) to earlier times in the year. The shift amounts to a full day over the course of about 70 years. This shift is largely compensated by the century leap year rule of the Gregorian calender.

As we approach the equinox the rate of change in the length of a day increases. If you follow the time periods of daylight you will notice that they change most slowly around the times of the solstices but change most rapidly at the equinoxes. At the poles this means that the rate of change is instantaneous. The equinox marks the transition from 24 hrs sunlight to 24 hrs darkness. The further you travel from the poles the slower the rate of change. At the equator the rate of change is mere seconds per day. This apparent "midnight sun" in its full effect can be seen up to 100 kms from the poles. The time from the solstice in June to the September equinox is 94 days. The time from the December solstice to the March/Vernal equinox is only 89 days. This discrepancy arises because the orbit of the Earth is elliptic rather than perfectly circular. This means that the rate at which the Earth orbits the Sun also varies. It is faster towards the spring(northern hemisphere) when the Earth is closer to the Sun.

The actual times of daylight and night are not equal at the time of the equinox. This is not just because the equinox is a point in time. It is also due to other factors that contribute to the day being longer than the night at this time of year. First of all, the Sun is not a point source of light. It is a disc, and sunrise and sunset are defined from the point of view of the upper edge of the disc. The discrepancy is at least a minute on both ends of the day. There is also the effect of light refraction when the Sun is near the horizon. This makes the Sun seem to be a little bit more above the horizon at both sunrise and sunset. This effect adds almost seven minutes to the daylight. If you take twilight into account the "day" at the time of the Equinox would be almost an hour longer than the night. As you go towards the poles this difference increases, and the time of the equinox has much more day than night.

INTERESTING EQUINOX FACTOIDS:

There are a number of other interesting things about the equinoxes:

*Equinoxes have a temporary disruptive effect on geostationary communications satellites. This happens because there is a point in time at the equinoxes when the Sun is directly behind the satellite from the point of view of receiving stations on Earth. The Sun's radiation overwhelms the much weaker signal from the satellite with noise. The duration of this effect varies. it may last only a few minutes, but it may persist up to an hour.

*There are a number of other names for the two equinoxes rather than spring/Vernal equinox and autumnal/fall equinox. These names suffer from the fact that they are obvious references to matters only in the northern hemisphere. South of the equator the situation of the seasons is precisely the opposite. Some have proposed using 'March Equinox' and 'September Equinox'. This is familiar to those who use the western solar based calender, but lunar calenders such as the Jewish or Muslim calenders have the equinoxes falling in different months from year to year. The equinoxes were once named in astrology as the 'First Point of Aries' and the 'First Point of Libra'. Because of precession these astrological signs are no longer the constellations where the equinoxes actually occur. Today they are the 'Pisces Equinox' and the 'Virgo Equinox'. One hardly ever hears such terms in common usage. Finally, there are the 'Northward Equinox' and the 'Southward Equinox', referring to the direction of the apparent motion of the Sun at each equinox. These terms are also rarely used.

*There is a persistent folk legend that the equinoxes are the only time of the year when you can stand an egg on end. This myth has been thoroughly debunked by the owner of the Bad Astronomy Blog who devotes a lot of his efforts to exposing hoaxes, myths and misconceptions in the area of astronomy. In actual fact you can stand an egg on end at any time of year. It just takes a little practice and skill. See the article at http://www.badastronomy.com/bad/misc/egg_spin.html

*Because the Sun is not a point source of light it actually takes the Sun about two and 1/2 days to cross the equator. The equinox is defined as the time when the midpoint of the Sun's disc is over the equator.

*A couple of good references on things equinoxal:

1)Details about the length of day and night at the equinoxes.

2)Calculation of length of day.

3)Table of times for equinoxes, solstices, perihelion and aphelion in 2000-2020.

COMING SOON AT MOLLY'S BLOG: SHINE ON HARVEST MOON: WEDNESDAY,SEPTEMBER 26TH

EQUINOXES:

At the time of the Spring (Vernal) Equinox this year Molly posted on matters concerning equinoxes in general. To read this before the upcoming event go to http://mollymew.blogspot.com/2007/03/welcome-to-spring-today-at-0007.utc.html .

As I said, more later.

FALL EQUINOX:

WELCOME TO AUTUMN:

The Fall Equinox will arrive this Sunday, September 23rd at 4:51 am. The Equinox is the exact time when daylight and nighttime are exactly equal or rather when the Sun is directly overhead at the equator.The "day" of closest equality of night and day is actually something quite different-the "equilux". This day is about three days later than the equinox in the fall and three days earlier than the spring equinox.The autumn equinox is a time for celebration and a "gathering-in". Stay tuned to Molly's Blog for more on this event.

WELCOME TO SPRING:

Today, at 00:07 UTC (19:07- 7:07 pm Winnipeg Time) the change of seasons has occurred, and it is now officially spring (yah, cheer, rah).

Molly spent the better part of today driving around and listening to the founts of all wisdom on the radio try their best to give the right time, almost always failing. The actual time is easily looked up, and if readers from other localities are interested in when it occurred in their time zone they can use the Time and Date.com site under our 'Other Interesting Sites' section to calculate the time difference between UTC and their time zone.

The equinoxes, from the latin equus(equal) and nox (night), are the two times each year when the sun spends an equal amount of time above and below the horizon. In actual fact the day at this time is longer than the night because the sun is not a "point" source of light, and when the centre of the solar disc is below the horizon the upper edge is still visible. Also refraction means that the sun's rays reach the ground even when the whole disc is below the horizon. At the equator this means that the day is about 14 minutes longer than the night at the equinox, and as you go towards the poles the difference becomes greater and greater.

The Spring Equinox has several alternative names ie the March Equinox, the Vernal Equinox, the First Point of Aries (an obsolete astrological term because precession has led to a total disjuncture between astrology and the actual position of the constellations), the Pisces Equinox (present position of the equinox) and the Northward Equinox. It should be noted that the term "equinox" refers to a moment in time, not a day. The rate of change of daylight versus nighttime is greatest at the time of the equinoxes. At the equator the rate of change is zero while at the poles the equinoxes mark the change from 24 hours of night or day to its opposite. The equinoxes fall about six hours later every years but are "reset" by the leap year inserted in the Gregorian calender. This itself varies as the Gregorian calender is not 100% accurate. Small changes also occur due to the gravitational influence of other bodies in the solar system, particularly the Moon. Because of the shift of the time of the equinoxes (and solstices) the present most common day for the Vernal Equinox is March 20th (as it is this year). Older people such as Molly have the date March 21st stuck in their minds because the equinox did indeed come earlier back in the days when Molly was a wee kitten.

The Spring Equinox has been associate with a great number of Spring festivals in many cultures and many ancient cultures devoted considerable effort in building "observatories" to calculate the exact time. In ancient German religion the vernal equinox was the time when Ostara, the goddess of fertility and the Moon mated with the solar god to produce a child due to be born 9 months later on "Yule". In ancient Greece this equinox marked the return of Persephone from the Underworld. The Mayans in Central America celebrate a spring festival that dates back a thousand years to the ancient "return of the Sun Serpent". the ancient cultures of the Middle East (Babylonian, Sumerian, Elamite and Persian) considered this day as their "New Years' Day", and this is still preserved in the Iranian and Bahai calenders. This marking of New Years at this time is common to many other countries in Central Asia such as Afghanistan, Azerbaijan, etc. and is a holiday in many countries where it is not accepted as the date of the New Year.

In Saxon mythology, from which many modern day Wiccan myths are derived, the goddess Eostre (from whom derives the word "estrogen") had her feast day on the full Moon following the vernal equinox. The present Christian calculation of "Easter" (also derived from her name) as the first Sunday after the full Moon on or after the Spring Equinox was derived from the appropriation of this festival. One interesting legend about Eostre is that she once found a dying bird on the ground one winter and in order to save it she transformed it into a rabbit. But the transformation wasn't complete, and the rabbit retained the ability to lay eggs which it would decorate and leave as gifts for Eostre. Now you know from whence comes the Easter Bunny.....

Christianity also borrowed from the ancient pagan religions to place the Feast of the Annunciation on the date of March 25th by the old Julian calender. This led to the further appropriation of Yule, December 25th, some 9 months later in imitation of the old Teutonic calenders, as the time of the birth of Jesus.

Elsewhere, Japan has the day of the Spring Equinox as a national holiday. In many Arab countries this equinox is celebrated as Mothers' Day. Earth Day was originally celebrated on March 21st, but more recently it has been moved to April 22nd. A few other pieces of trivia follow.

In some European countries legend has it that the equinox is the only time when one can successfully balance an egg on its end. during the equinox geostationary communication satellites may temporarily "go down" as the radiation of the Sun directly behind them disrupts their signals. The actual day when daytime and nighttime are closest to equal is referred to as the "equilux" as opposed to the equinox. This is usually three or four days "towards the winter" ie it fell three days earlier this year as opposed to the equinox.

For those who enjoy total trivia there is a table of times for the spring equinox from 1452 to 2547 at http://ns1763.ca/equinox/eqindex.html .

ANYWAYS, HAVE A GOOD SPRING

MOLLY