Humanity lives confined to a blue planet we call "Earth"
because it is the element on which we uphold and gives us stability
Although the dominant element is the water
The Earth has a number of periodic motions
Of these, the most important because of their intensity are two:
the rotation about its own axis and travel around the sun.
These movements originate cycles in which we are all engaged:
the movement of rotation is what gives rise to the day and night and lasts 24 hours;
the movement of translation is the cause of the cycle of the seasons and lasts 365 days, ie one year.
The cause of existing seasons lies in the special provision of the axis of rotation of the earth.
The imaginary red line that surrounds the Earth is Equator.
Equator is a fundamental level that is adopted in astronomy to perform calculations of position,
both on the surface of the earth as in heaven.
The coordinates calculated on the basis of this level are called "Equatorials Coordinates"
The line of poles is perpendicular to the level,
and is the line around which the Earth rotates.
If we make visible the level of the orbit of the earth around the sun
and what we projected in space until they cut the globe,
we will see that makes with Equator on Earth an angle of 23 degrees and a half or so.
This is called "obliquity of the ecliptic"
This angle causes the earth at its annual cycle, orients their poles toward the sun.
In the picture you can see the tilt of the Earth during the winter.
The level of the ecliptic is projected on the South.
The North Pole is farthest from the Sun to the South Pole.
If we look at the level of the ecliptic, the position of the earth would be as shown.
It shows how the southern hemisphere receives sunlight more directly,
Is the Austral Summer,
while the northern hemisphere receives the light so oblique stroke:
is the winter North.
Placing ourselves in the sun, this is reflected in the animation we see now
if we see the line of Equator on the level of the ecliptic, it is summer in the South ...
When the line goes, it is winter there and summer in the Northern Hemisphere
When two planes intersect in front of us, it will be the beginning of the Fall or Spring
we are talking about the equinoxes.
If we see the earth in a schematic, as in the following images,
we’ll see better what we mean.
The ecliptic is represented here as a circle of green.
It is, in fact, the projection of the level in which the earth moves around the sun.
In the same way, if we project the position of sun each day throughout the year,
We can see how it moves through that line, occupying different positions.
In the picture, the sun is represented by the small yellow circle.
We start of the Winter Solstice (0 degrees Capricorn), an area south declination.
The sun will move forward until cross with Equator in the Vernal (0 degrees Aries)
spring equinox.
Then advance to to the Summer Solstice, the highest declination North (O degrees Cancer)
and descends from here, returning to cross the level of Equator in the Autumn Equinox (0 degrees Libra)
falling again to Capricorn, completing the annual cycle.
These points of maximum and minimum from the sun determine two very important parallel levels:
the Tropic of Cancer and the Tropic of Capricorn.
Both represent the maximum latitude to reach the sun throughout the year.
The Tropic of Cancer is at 23 degrees 27' North Latitude and
the Tropic of Capricorn at 23 degrees 27' South latitude.
We have located astronomically, therefore, the two solstices (Cancer and Capricorn)
and the two equinoxes (Aries and Libra).
These points mark the beginning of the season.
