First Day of Spring

 

March 20th was the First Day of Spring

The Vernal Equinox marks the official first day of Spring which Officially began at 1:14 AM CDT Tuesday morning. 

An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the Sun being vertically above a point on the Equator. The term equinox can also be used in a broader sense, meaning the date when such a passage happens. The name "equinox" is derived from the Latin aequus (equal) and nox (night), because around the equinox, the night and day are approximately equally long. It may be better understood to mean that latitudes +L and -L north and south of the equator experience nights of equal length.

 

At an equinox, the Sun is at one of two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points: the vernal point and the autumnal point. By extension, the term equinox may denote an equinoctial point.

An equinox happens each year at two specific moments in time (rather than two whole days), when there is a location on the Earth's Equator where the centre of the Sun can be observed to be vertically overhead, occurring around March 20/21 and September 22/23 each year.

 

 

 

 

lmx

Why Do We have Seasons?

 

As the earth spins on its axis, producing night and day, it also moves about the sun in an elliptical (elongated circle) orbit that requires about 365 1/4 days to complete. The earth's spin axis is tilted with respect to its orbital plane. This is what causes the seasons. When the earth's axis points towards the sun, it is summer for that hemisphere. When the earth's axis points away, winter can be expected. Since the tilt of the axis is 23 1/2 degrees, the North Pole never points directly at the Sun, but on the summer solstice it points as close as it can, and on the winter solstice as far as it can. Midway between these two times, in spring and autumn, the spin axis of the earth points 90 degrees away from the sun. This means that on this date, day and night have about the same length: 12 hours each, more or less.

Why should this tilt of the Earth's axis matter to our weather? To understand this, take a piece of paper and a flashlight. Shine the light from the flashlight straight onto the paper, so you see an illuminated circle. All the light from the flashlight is in that circle. Now slowly tilt the paper, so the circle elongates into an ellipse. All the light is still in that ellipse, but the ellipse is spread out over more paper. The density of light drops. In other words, the amount of light per square centimeter drops (the number of square centimeters increases, while the total amount of light stays the same).

The same is true on the earth. When the sun is overhead, the light is falling straight on you, and so more light (and more heat) hit each square centimeter of the ground. When the sun is lower in the sky, the light gets more spread out over the surface of the earth, and less heat (per square centimeter) can be absorbed. Since the earth's axis is tilted, the sun is higher when you are on the part of the earth where the axis points more towards the sun, and lower on the part of the Earth where the axis points away from the sun.

For the Northern Hemisphere, the axis points most toward the sun in June (specifically around June 21), and away from the sun around December 21. This corresponds to the Winter and Summer Solstice (solstice is Latin for "the sun stands"). For the Southern Hemisphere, this is reversed.

For both hemispheres, the earth is 90 degrees away from the sun around March 21 and then again around September 21. This corresponds to the Fall and Spring Equinox (equinox is Latin for "equal night"). Everyplace in the world has about 12 hours of daylight and 12 hours of night.Image showing the Earth's orbit 

 

 

 

 

 

 

 

 

 

 

So why are sunrise and sunset not exactly 12 hours apart on the Equinox?

Day and night are not exactly of equal length at the time of the March and September equinoxes. The dates on which day and night are each 12 hours occur a few days before and after the equinoxes. The specific dates for this occurrence are different for different latitudes.

On the day of the equinox, the geometric center of the Sun's disk crosses the equator, and this point is above the horizon for 12 hours everywhere on the Earth. However, the Sun is not simply a geometric point. Sunrise is defined as the instant when the leading edge of the Sun's disk becomes visible on the horizon, whereas sunset is the instant when the trailing edge of the disk disappears below the horizon. At these times, the center of the disk is already below the horizon. Furthermore, atmospheric refraction (or bending) of the Sun's rays cause the Sun's disk to appear higher in the sky than it would if the Earth had no atmosphere. Thus, in the morning, the upper edge of the disk is visible for several minutes before the geometric edge of the disk reachs the horizon. Similarly, in the evening, the upper edge of the disk disappears several minutes after the geometric disk has passed below the horizon.

For observers within a couple of degrees of the equator, the period from sunrise to sunset is always several minutes longer than the night. At higher latitudes in the Northern Hemisphere, the date of equal day and night occurs before the March equinox. Daytime continues to be longer than nighttime until after the September equinox. In the Southern Hemisphere, the dates of equal day and night occur before the September equinox and after the March equinox.

When are the times and dates of the next equinoxes and solstices?

The chart shown below shows the dates and times for the equinoxes and solstices through 2012. Times listed are in Eastern Time.  Subtract one hour for Central Time.

Year Spring Equinox Summer Solstice Fall Equinox Winter Solstice
2012 Mar 20 -- 1:14 am June 20 -- 7:09 pm Sept 22 -- 10:49 am Dec 21 -- 6:12 am
2013 Mar 20 -- 7:02am June 21 --  1:04am Sept 22 -- 4:44pm Dec 21 -- 12:11pm
2014 Mar 20 -- 12:57pm June 21 -- 6:51am Sept 22 -- 10:29pm Dec 21 -- 6:03pm
2015 Mar 20 -- 6:45pm June 21 -- 12:38pm Sept 23 -- 4:21am Dec 21 --  11:48pm
2016 Mar 20 -- 12:30am June 20 --  6:34pm Sept 22 -- 10:21am Dec 21 --  5:44am
2017 Mar 20 -- 6:29am June 21 -- 12:24am Sept 22 -- 4:02pm Dec 21 -- 11:28am
2018 Mar 20 -- 12:15pm June 21 -- 6:07am Sept 22 --  9:54pm Dec 21 -- 5:23pm
2019 Mar 20 -- 5:58pm June 21 -- 11:54am Sept 23 -- 3:50am Dec 21 -- 11:19pm
2020 Mar 19 -- 11:50pm June 20 -- 5:44pm Sept 22 -- 9:31am Dec 21 -- 5:02am

 

Is it true that you can stand an egg on

 

 

 

 

sgx---

...Spring Arrived Yesterday - March 20th...

March 20th was the First Day of Spring

The Vernal Equinox marks the official first day of Spring which Officially began at 1:14 AM CDT Tuesday morning. 

An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the Sun being vertically above a point on the Equator. The term equinox can also be used in a broader sense, meaning the date when such a passage happens. The name "equinox" is derived from the Latin aequus (equal) and nox (night), because around the equinox, the night and day are approximately equally long. It may be better understood to mean that latitudes +L and -L north and south of the equator experience nights of equal length.

The word is also used for the same event happening on other planets and in setting up a celestial coordinate system; see equinox (celestial coordinates).

At an equinox, the Sun is at one of two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points: the vernal point and the autumnal point. By extension, the term equinox may denote an equinoctial point.

An equinox happens each year at two specific moments in time (rather than two whole days), when there is a location on the Earth's Equator where the centre of the Sun can be observed to be vertically overhead, occurring around March 20/21 and September 22/23 each year.

For more information on the Vernal Equinox go to http://www.glyphweb.com/esky/concepts/vernalequinox.html

 abq ---

The 2012 Equinoxes
There are only two times of the year when the Earth's axis is tilted neither toward nor away from the sun, resulting in a "nearly" equal amount of daylight and darkness at all latitudes. These events are referred to as Equinoxes and will occur on March 19th at 1114 pm MDT (Vernal Equinox - the first day of Spring) and again on September 22nd at 849 am MDT (Autumnal Equinox - the first day of fall).  The word equinox is derived from two Latin words - aequus (equal) and nox (night). At the equator, the sun is directly overhead at noon on these two equinoxes.  The "nearly" equal hours of day and night is due to refraction of sunlight. or a bending of the light's rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon.  Additionally, the days become a little longer at the higher latitudes (those at a distance from the equator) because it takes the sun longer to rise and set.  Therefore, on the equinox and for several days before and after the equinox, the length of day will range from about 12 hours and six and one-half minutes at the equator, to 12 hours and 8 minutes at 30 degrees latitude, to 12 hours and 16 minutes at 60 degrees latitude.

The 2012 Solstices

The winter solstice marks the shortest day and longest night of the year.  In the Northern Hemisphere, it occurs when the sun is directly over the Tropic of Capricorn, which is located at 23.5° south of the equator and runs through Australia, Chile, southern Brazil, and northern South Africa. The summer solstice marks the longest day and night of the year. It is directly over the Tropic of Cancer, located at 23.5° north of the equator.  This year, the Northern Hemisphere summer solstice will occur at 509 pm MDT on June 20th. The winter solstice will occur at 412 am MST on December 21st. For a complete listing of the dates of the winter and summer solstice's and spring and fall equinox's through 2020, check out this site from the U.S. Naval Observatory.

The Seasons

We all know that the Earth makes a complete revolution around the sun once every 365 days, following an orbit that is elliptical in shape.  This means that the distance between the Earth and Sun, which is 93 million miles on average, varies throughout the year.  During the first week in January, the Earth is about 1.6 million miles closer to the sun. This is referred to as the perihelion.  The aphelion, or the point at which the Earth is about 1.6 million miles farther away from the sun, occurs during the first week in July.  This fact may sound counter to what we know about seasons in the Northern Hemisphere, but actually the difference is not significant in terms of climate and is NOT the reason why we have seasons.  Seasons are caused by the fact that the Earth is tilted on its axis by 23.5°.  The tilt's orientation with respect to space does not change during the year; thus, the Northen Hemisphere is tilted toward the sun in June and away from the sun in December, as illustrated in the graphic below. 



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