Tuesday, September 22, 2015

Autumn Begins Early Wed. Morning


Earth rotating during the Autumnal Equinox.
Incoming solar energy is equal in both the Northern
and Southern Hemispheres.
(Image Source: NOAA)

By Glenn A. Walsh
Reporting for SpaceWatchtower

The Autumnal Equinox, the beginning of the season of Autumn or Fall in the Northern Hemisphere of Earth, begins early Wednesday Morning, 2015 September 23 at 4:20 a.m. Eastern Daylight Saving Time (EDT) / 8:20 Coordinated Universal Time (UTC).

In Earth's Southern Hemisphere, this marks the astronomical beginning of the season of Spring.

On the day of Equinox, the Sun appears directly overhead at local Noon on the Equator. At the moment of Equinox, the Northern and Southern Hemispheres of Earth are illuminated equally. And, the time of Equinox is the only time when  the terminator (dividing line on Earth between daylight and darkness) is perpendicular to the Equator.

This, and the reason for seasons on Earth in the first place, is due to the fact that Earth rotates on its axis, which is tilted at an approximate 23.44-degree angle from the plane of the Earth's orbit around the Sun. As the Earth revolves around the Sun, this axial tilt causes one hemisphere of the planet to receive more direct solar radiation during that hemisphere's season of Summer and much less direct solar radiation a half-year later during that hemisphere's season of Winter. As mentioned, during an Equinox (about half-way between Summer and Winter, and about half-way between Winter and Summer) both planetary hemispheres receive an equal amount of solar radiation.

An urban legend that has been making the rounds for decades has it that eggs can be stood on their ends only during an Equinox, whether the Vernal Equinox in the Spring or the Autumnal Equinox in the Fall. This is completely false. Depending greatly on the size and shape of the particular egg, eggs can be stood on their ends any day of the year! Astronomy has nothing to do with whether an egg can stand on its end. If an egg can stand on its end on the Equinox (and, due to the shape and size of some eggs, this is not even possible), it can stand the same way any other day of the year.

In the last few years, with the help of the Internet and Social Media, another urban legend has become prevalent. Now it is claimed that brooms can stand, on their own, on their bristles, only on an Equinox day. This is also false. Again, as with eggs, if a broom can stand on its bristles by itself (this usually only works with newer brooms, with more even bristles) on an Equinox, it can do so any day of the year!

September 23 is also designated as the 8th annual Falls Prevention Awareness Day.

More on the Autumnal Equinox:
Link >>> http://scienceworld.wolfram.com/astronomy/AutumnalEquinox.html

More on the season of Autumn or Fall: Link >>> http://en.wikipedia.org/wiki/Autumn

More on an Equinox: Link >>> http://en.wikipedia.org/wiki/Equinox

More on Earth's Seasons: Link >>> http://en.wikipedia.org/wiki/Season

More on the tilt of a planet's axis: Link >>> http://en.wikipedia.org/wiki/Axial_tilt

More on the urban legend of eggs and brooms standing on their own, only on an Equinox:
Link >>> http://www.snopes.com/science/equinox.asp

More on Falls Prevention Awareness Day: Link >>> http://www.ncoa.org/improve-health/center-for-healthy-aging/falls-prevention/falls-prevention-awareness.html

Special Thanks: Eric G. Canali, former Floor Manager of Pittsburgh's original Buhl Planetarium and Institute of Popular Science and Founder of the South Hills Backyard Astronomers amateur astronomy club.

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.

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gaw

Glenn A. Walsh, Project Director,
Friends of the Zeiss < http://buhlplanetarium.tripod.com/fotz/ >
Electronic Mail - < gawalsh@planetarium.cc >
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Author of History Web Sites on the Internet --
* Buhl Planetarium, Pittsburgh:
  < http://www.planetarium.cc >
* Adler Planetarium, Chicago:
  < http://adlerplanetarium.tripod.com >
* Astronomer, Educator, Optician John A. Brashear:
  < http://johnbrashear.tripod.com >
* Andrew Carnegie & Carnegie Libraries:
  < http://www.andrewcarnegie.cc >
* Civil War Museum of Andrew Carnegie Free Library:
  < http://garespypost.tripod.com >
Duquesne Incline cable-car railway, Pittsburgh:
  < http://inclinedplane.tripod.com >
* Public Transit:
  < http://andrewcarnegie2.tripod.com/transit >

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