Basics keys of sky english version

Uploaded by agestevez on 11.06.2012

Naked eye astronomy
Have you asked any night, walking through an area without light pollution, how can you know the sky, just looking it? ...
At first sight, the sky is able to give you much information ... if you know how to interpret it.
If you are patient, we will give some keys.
But we where to start? ...
The date is important
Imagine you are in the field, at night and only know the day, the date that is ...
Then you know a lot ...!!!
In the first place, the date that you live tells you, without tables or papers, or special documentation
the position of Earth in its orbit around the Sun
And if you know this information, you know many others.
Knowing where the sun, we know where is the Earth, because Earth is located diametrically opposite to the solar degree of the ecliptic.
We must remember that, although it seems that moves the sun, the move is really of the earth.
Let's start:
Earth makes a complete circle every year to its orbit.
It was established that the orbit starts on March 21th, when the Earth crosses the celestial Ecuador.
This point is called the Aries Point, or Point-Vernal
and the day is known as "Spring Equinox" or first day of Spring.
The ecliptic is usually divided (for thousands of years, because the invention is due to the Sumerians)
in twelve sectors of 30º each.
Each sector corresponds to a zodiac sign.
Returning to the vernal equinox ...
... What about that day? ... or better, that night? ...
The long of this day is exactly the same as the night because the sun is in Equator.
The sun that day is coming into the north zone of the ecliptic,
from south declination to north declination.
From there, the Sun will be 6 months in the northern zone.
How fast is the Sun (ie, Earth)?...
... About 1 degree every day.
This means that 21th of every month, approximately the sun will change the sign of the zodiac ...
because each sign occupies 30 degrees from the ecliptic.
2000 years ago the constelations coincided in the sky with sectors of the ecliptic that have lent their names to them
(And not viceversa, as they say).
Not now.
Aries Point has been delaying the rate of about 50''per year.
Now the Aries point coincides with the Pisces constellation towards the end of it
and soon will enter in the Aquarius constellation.
Each sector of the ecliptic (ie, each sign of the zodiac) has shifted the same number of degrees backwards.
This retrograde motion is called "Precession of the Equinoxes"
and is one of the seven movements of the Earth.
But, look at the sky.
Suppose that today is March 21th.
If the sun is that day in the first degree of Aries,
only we can see the opposite night sky,
the sky of Libra.
In reality, we will see the sky of the Virgo constellation, because we know that is displaced.
In the picture we see how, anyone who observes the sky, situated at the Horizon,
see the sun appear in the east,
and, with the passing hours,
the Sun rises to the zenith
and then descends to the western horizon,
disappearing here.
The ideal scenario we will look for is when the sun reaches the nadir,
ie, the contrary point to the Zenit, and that is below the earth.
At such times, as can be seen, at the zenith we have the opposite grade of the Sun:
the Libra sector of the ecliptic, or degree 180.
If we do the same on June 21th,
day of the Summer Solstice
the sun will be in the first degree of Cancer.
Therefore, we can see, at night, the part of Heaven for Capricorn
and the constellation of Sagittarius.
On September 21th,
the Sun will be in the first degree of Libra
and that night you can see the Aries sky the constellation of Pisces.
On December 21th,
the Sun will be in the first degree of Capricorn
and that night at the zenith we can see the Cancer sky with the constellation of Gemini.
Where will the sun on May 12th?:
is easy to deduce, if the previous 21 day (corresponding to April) the sun was at 0 degrees of Taurus,
on May 12th will be approximately over 21º of Taurus.
because 30 days of April - 21 are 9, 9 plus 12 equals 21.
Where will the sun on January 1th?:
On December 21th was at 0° of Capricorn ...
Then, between December 31th and 21th are 10,
a degree per day,
plus one additional degree, the Sun will be at 11º of Capricorn.