Claves básicas de la Luna - astronomía a simple vista II versión española

Uploaded by agestevez on 26.09.2010

Astronomy with the naked eye
Basic keys of the Moon
The Moon is the Earth's natural satellite.
In its movement around our planet,
the Moon takes approximately 28 days to make a full turn.
When we look at the moon, we can not do it without look at the sun,
because the moon reflected us back more or less light
depending on the angle it makes with him.
The variation of this angle is what gives rise to the lunar phases.
We must make clear an idea: in the lunar phases are involved three celestial objects:
The Moon, which reflects light, the Sun than emits, and the Earth from where we look.
The Phases exists for our relative position against the two bodies.
The Moon moves very close to the plane of the ecliptic.
His movement is very complex since has 1475 oscillations and periodic irregularities
which are the result of attraction of the Earth, the Sun and planets
but for the effects that interest us, suffice it to say that the Moon and the Sun they travel the same path in their orbits.
Recall that the Sun appears to move along the ecliptic, but it's actually the Earth that makes moving
and what we see is a projection on the sky.
Both bodies on move in the same direction, from west to east,
moving along the ecliptic in a direct sense, advancing from the Vernal Point, each in its natural rhythm.
The natural rhythm of the moon is about 12 or 13 degrees per day.
That is, an observer what see the moon one night at a point at the sky
can see how the next night at the same time, the Moon will moved 12 or 13 degrees to the east.
And if you make this observation several nights, may determine that happens every day.
Knowing the rate at which the moon moves,
we know how long it takes to complete its orbit around the Earth ...
If we divide the 360 degrees of the ecliptic by 12.5,
get 28.8 which are the days it takes the Moon to perform the complete cycle.
This time it is called "Sidereal Orbital Period".
The observer will notice that the moon rises in the horizon every day about an hour later. What is this? ...
We will study the situation in the chart.
Suppose one day, the Moon is, say, in grade 0 ° of the Ecliptic.
This degree is already well known by all of us
because it is the Vernal Point and we know that is late constellation of Pisces.
An observer will see the Moon at a certain time, for that day
when the observer's horizon crosses that degree of the ecliptic.
This movement is due to the Earth's rotation on itself.
Well, let's say that time is 12 pm.
The moon is rising over the horizon,
reaches the zenith and a few hours later disappears from the west.
A day passes.
During that day, the Moon has moved 12 or 13 degrees to the east.
When the time comes, the Horizon reached grade 0° of the Ecliptic,
but the moon is not there ... it is 12.5° below ...
the horizon has to travel 12.5º more to find the moon.
How many degrees every hour moves the Horizon?...
if in one day makes a complet circle...
360º is 24 hours ...
Then, in an hour, will travel 360/24 = 15º,
15º per hour.
But the moon does not go through 15 degrees if its speed is 12.5° ...
so it is easy ... If Horizonte runs 15º in an hour How long it takes to travel 12.5º?...
if 15º runs in 60 minutes then 12.5º will travel in X.
so (12.5*60)/15 gives us about 50 minutes
This means that the Horizon will take about 50 minutes plus, every day, in the finding the moon.
The different speeds of the Moon and the Sun
makes that the first forward every month to the second in the common path followed in the sky.
From the Earth this is seen looking at the moon more or less illuminated, depending on the angle it makes with the Sun (as seen from Earth).
In the animation we see below, the moon is in the same degree of the ecliptic as the Sun
In astronomical terms, this is a "conjunction."
The moon is hidden because all the sunlight falling on the outer face and from the Earth is not seen.
This phase is known as "New Moon" or "Dark Moon"
and is described from millennia in the myths of "Hecate" and "Lilith".
Over the day, the Moon is separating from the Sun and the illuminated area grows (as seen from Earth)
until it reaches 90º from the Sun
For astronomers, this angle is called "quadrature"
and the moon has reached the stage of "First Quarter".
It has been nearly a week since from the New Moon.
The moon moves on, increasing the angular distance to the Sun and going through the "Waning Gibbous"
up to 180º from the Sun
in which the moon shines in all its splendor, showing all its illuminated surface.
This "Full Moon" is the result of the "opposition" to astronomers.
At this time, when the sun rises, the Moon sets and vice versa.
It has been almost 14 days since the New Moon.
In many myths, passed down through the centuries, it is said that the Full Moon affecting men, animals and plants
although science will not admit it.
The Moon is elusive and how it affects one emotionally, its effects are difficult to measure.
Continuing his travel, the Moon begins his back to the Sun,
light falling on its surface when approaching 90°,
again passing through the phase "Waning" and reaching another "Quarter"
this time "Waning Crescent Moon".
In spain it is said that "The Moon is lying", because when we see it in heaven with "D" form
it is "Creciente" ("Growing") and when we see the shape of "C" is "Decreasing".
Finally, to rise to 28 days, how the moon turns to meet the sun?.
No, because during that time the Sun has moved at a rate of a degree per day and during those 28 days has moved about 28 degrees.
To the moon costs two days and more to reach the Sun
and therefore the lunar month lasts 29 days, 12 hours, 43 minutes and 12 seconds. This is what is known as the "Synodic Month"
When the moon is in New Moon phase, Sun and Moon are together in the sky,
so both will rise when the Horizon will cross the degree of the ecliptic in which they are and will be see during the day.
In the following images we can see what we say:
The moon will appear next to the sun during the day, revealing the narrow illuminated area.
When approaching First Quarter Phase, the sun will set before the moon
and you can see the moon shining in the first part of the night.
When it's full moon, this will come over the horizon when the Sun disappears in the west, and the moon will disappear at daybreak.
In the phase of "Last Quarter", the Moon will see it first Horizon and will be followed by the Sun
In the exact quadrature, the sun will rise when the moon is at its zenith.
Some images of the Sun and Moon extracted from the NASA web