This diagram shows the position of the Earth, in relation to the Sun,
at the time of the Autumnal Equinox, as well as the other solstices and
equinox of the year.
(Image Source: ©1999,
Eric G. Canali, former Floor Operations Manager of Pittsburgh's original Buhl
Planetarium and Institute of Popular Science and Founder of the South
Hills Backyard Astronomers amateur astronomy club; permission granted
for only non-profit use with credit to author.)
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 Saturday evening. In Earth's Southern Hemisphere, this equinox marks the
astronomical beginning of the season of Spring. And, the Harvest Moon in the Northern Hemisphere, the Full Moon of September, is on Monday evening.
September Equinox
The September Equinox occurs on Saturday Evening, 2018 September 22 at 9:54 p.m. Eastern
Daylight Saving Time (EDT) / September 23, 1:54 Coordinated Universal
Time (UTC).
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 Earth 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.
Although "Equinox" in
Latin means equal-night, the day of the Equinox does not actually
have an equal amount of daylight and nightfall, as it appears on the
Earth's surface. If the Sun was just a pin-point of light in our sky,
as all other stars appear, day and night would be equal.
But, because the Sun is a disk, part of
the Sun has risen above the horizon before the center of the Sun
(which would be the pin-point of light); so there are extra moments
of light on the Equinox. Likewise, part of the Sun is still visible,
after the center of the Sun has set.
Additionally, the refraction of
sunlight by our atmosphere causes sunlight to appear above the
horizon, before sunrise and after sunset.
September 25 will mark the Equilux
("equal-light"), the actual day with equal hours and
minutes of the Sun above the horizon, and equal hours and minutes of
the Sun below the horizon. The Equilux occurs twice each year,
approximately 3-to-4 days before the Vernal Equinox, when Spring begins, and 3-to-4 days
after the Autumnal Equinox.
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 22 is also designated as the
annual Falls Prevention Awareness Day for this year.
Harvest Moon
This year's Harvest Moon will occur on Monday Evening, 2018 September 24 at 10:52 p.m. EDT / September 25 at 2:52 UTC. Often, but not always (usually, two out of every three years), the
September Full Moon is considered the Harvest Moon. The Harvest Moon is
the Full Moon closest to the Autumnal Equinox, when the season of Autumn
or Fall officially begins, usually September 22 or 23.
So, the Harvest Moon, in general, can occur from two weeks before the
Autumnal Equinox to two weeks after the beginning of Fall. When the
October Full Moon occurs early in the month, it is then sometimes
considered the Harvest Moon. The October Full Moon, which is usually the
first Full Moon after the Harvest Moon, is usually considered the
Hunter's Moon, providing hunters with additional light to hunt game
after sunset. When the October Full Moon is considered the Harvest Moon,
some still consider it the Hunter's Moon as well, while others then
consider the November Full Moon the Hunter's Moon.
Occurring in the late Summer or early Autumn, in September or October in
the Northern Hemisphere, the Harvest Moon provides farmers with
additional light in the early evening, during the very busy harvest
time. The Harvest Moon has the same characteristics in the Southern
Hemisphere, when it occurs in March or April.
On average, throughout the year, the Moon rises 50 minutes later each
day. However, this lag time between successive Moon rises shrinks to an
annual minimum near the Full Moon closest to the Autumnal Equinox. This
greatly reduced lag time averages between 25 and 35 minutes throughout
most of the United States, and as little as 10 to 20 minutes for Canada
and much of Europe, each day for several days around the time of the
Full Moon. Hence, for a few days around the date of the Harvest Moon,
there is little or no period of darkness between sunset and Moon rise.
This provides farmers with several days of extra, uninterrupted, light
after sunset, for completing the harvest (of course,
weather-permitting).
In the Northern Hemisphere, the September Full Moon is also known as the
Corn Moon, Fruit Moon, Wild Rice Moon, and Red Plum Moon.
The September Full Moon has been given several names in the Southern
Hemisphere: Worm Moon, Lenten Moon, Crow Moon, Sugar Moon, Chaste Moon,
and Sap Moon.
Internet Links to Additional
Information ---
Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.
Saturday, 2018 September 22.
Like This Post? - Please Share!
More Astronomy & Science News - SpaceWatchtower Twitter Feed:
Link >>> https://twitter.com/spacewatchtower
Astronomy & Science Links: Link >>> http://buhlplanetarium.tripod.com/#sciencelinks
Want to receive
SpaceWatchtower blog posts in your in-box ?
Send request to <
spacewatchtower@planetarium.cc >.
gaw
Glenn A. Walsh --- <
http://buhlplanetarium2.tripod.com/weblog/spacewatchtower/gaw/ >
Electronic Mail: <
gawalsh@planetarium.cc >
Project Director, Friends of the Zeiss: <
http://buhlplanetarium.tripod.com/fotz/ >
SpaceWatchtower Editor / Author: <
http://spacewatchtower.blogspot.com/ >
Formerly
Astronomical Observatory Coordinator & Planetarium Lecturer,
original Buhl Planetarium & Institute of Popular Science (a.k.a. Buhl Science Center),
Pittsburgh's science & technology museum from 1939 to 1991.
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 >
