Vernal Equinox, the First Day of
Spring
!
By Dr. Harold Williams of Montgomery College Planetarium
http://montgomerycollege.edu/Departments/planet/ 12:57PM EDT March 20, 2014
Old Farmers Almanac Spring Equinox
Title slide
Sunrises and
Sunsets
for the Seasons
The
Sky Dome
Polaris
On the day of
an summer
solstice…
S
W
On the day of
an winter
solstice…
On the day of
an equinox…
E
From Dan Bruton, Ph.D., Associate Professor
Department of Physics & Astronomy
Stephen F. Austin State University
Box 13044 SFA Station
Nacogdoches, TX 75962-3044 [email protected] Office: (936)468-2360
N
Polaris,
North
Pole
W
S
Winter
Solstice,
South of East
Vernal or
Autumnal
Equinox,
EAST
Summer
Solstice,
North of East
N
E
Starting Points for the Sun
From Dan Bruton, Ph.D., Associate Professor
Department of Physics & Astronomy
Stephen F. Austin State University
Box 13044 SFA Station
Nacogdoches, TX 75962-3044 [email protected] Office: (936)468-2360
Obliquity of the ecliptic
• 23 ½ degrees, approximately, between day axis of
rotation and year axis of revolutionary orbit of the
earth about the sun
• Causes of the Seasons
• Seasons are caused by the tilt of the earths axis, 23
½ degrees, approximately.
• Seasons are not caused by the fact that the earths
orbit is not a perfect circle, but the earth’s orbit,
during the year, around the sun is slightly
elliptical.
• Cause of the Inequality of the length of the
Seasons
• The ellipticity of the earths orbit does cause the
Length of Seasons
•
•
•
•
Winter 88 days 23 hours 54 minutes
Spring 92 days 18 hours 26 minutes
Summer 93 days 15 hours 29 minutes
Autumn 89 days 20 hours
!
Sun and Earth closest to each other, perihelion
Around January 3 or 4
Sun and Earth most distant from each other,
aphelion Around July 4
Equinoxes and Solstices
• The Vernal (Spring) Equinox (about March 21):
The location where the Sun crosses the equator
when going from south of the equator to north of
the equator.
– Position of the Sun: R.A. 0h, Dec 0o
• The Summer Solstice (about June 21): The
location where the Sun is at its furthest north.
– Position of the Sun: R.A. 6h, Dec +23.5o
Equinoxes and Solstices
• The Autumnal (Fall) Equinox (about September
21): Where the Sun crosses the equator when
going from north to south.
– Position of the Sun: R.A. 12h, Dec 0o
• The Winter Solstice (about December 21): The
location where the Sun is at its furthest south.
– Position of the Sun: R.A. 18h, Dec –23.5o
Some Resources on Seasons
• Seasons in the Wikipedia http://
en.wikipedia.org/wiki/Seasons • Spring Seasons in the Wikipedia http://
en.wikipedia.org/wiki/Spring_%28season
%29 • Tropical Year in the Wikipedia http://
en.wikipedia.org/wiki/Tropical_year
People have known this for a long time.
Bas-relief in Persepolis. A Zoroastrian symbol of Nowruz - on the vernal equinox the powers of the eternally fighting bull (personifying the Earth) and lion (personifying the Sun) are equal.
Nowruz
Haft-Sin table
Haft-Sin table in Tehran, The Haft Sīn items are:
sabzeh - wheat, barley or lentil sprouts growing in a dish - symbolizing rebirth
samanu - a sweet pudding made from wheat germ - symbolizing affluence
senjed - the dried fruit of the oleaster tree - symbolizing love
sīr - garlic - symbolizing medicine
sīb - apples - symbolizing beauty and health
somaq - sumac berries - symbolizing (the color of) sunrise
serkeh - vinegar - symbolizing age and patience.
Other items on the table may include:
Sonbol - Hyacinth (plant)
Sekkeh - Coins - representative of wealth
traditional Iranian pastries such as baghlava, toot, naan-nokhodchi
Aajeel - dried nuts, berries and raisins
lit candles (enlightenment and happiness)
a mirror (symbolizing cleanness and honesty)
decorated eggs, sometimes one for each member of the family (fertility)
[68]
a bowl of water with goldfish (life within life, and the sign of Pisces which the sun is leaving). As an essential object of the Nowruz table, this goldfish is also "very ancient and meaningful" and with Zoroastrian connection.
rosewater, believed to have magical cleansing powers
the national colours, for a patriotic touch
a holy book (e.g., the Avesta, Qur'an,or Kitáb-i-Aqdas) and/or a poetry book (almost always either the Shahnameh or the Divan of Hafiz)
Jamshid ancient mythological figure of
Greater Iranian culture and tradition.
http://en.wikipedia.org/wiki/Jamshid
Polar Vortex
• Jennifer Francis - Understanding the
Jetstream Published on YouTube Feb 26,
2013
• http://www.youtube.com/watch?
v=_nzwJg4Ebzo 5 minutes 31 seconds!
• Rossby Wave
• Vorticity and Vorticity Equations
http://marine.rutgers.edu/~francis/
Easter
• The First Council of Nicaea (325)
established the date of Easter as the first
Sunday after the full moon (the Paschal Full
Moon) following the March equinox.
Ecclesiastically, the equinox is reckoned to
be on 21 March (even though the equinox
occurs, astronomically speaking, on 20
March in most years), and the "full moon"
is not necessarily the astronomically correct
date.