European Journal of Science and Theology, October 2013, Vol.9 , No. 5, 255-263 [617166]

European Journal of Science and Theology, October 2013, Vol.9 , No. 5, 255-263

_______________________________________________________________________
SOME ASPECTS ON THE EVOLUTION OF
ASTRONOMY

Gabriel Badescu* and Ovidiu Stefan

Technical University Cluj Napoca, North University Center Baia Mare, Dr. Victor Babes Street,
430083 Baia Mare, Romania
(Received 3 August 2013, revised 4 August 2013 )
Abstract

We show some a spects of the Astronomy evolution in general, and on its research and
measurement tools. We present the Earth from an astronomical and geodetic point of
view, the celestial sphere and astronomical coordinate systems. The conclusion is that
the evolution of A stronomy has been marked by different moments from the beginning
of humanity, ab out 30,000 years ago, until today.

Keywords: science , astronomy, astronomical coordinate systems

1. Introduction

If on a dark, cloudless night we look from a distant location, far away
from the city lights, the starry sky can be seen in its splendo ur and beauty. Thus
it is easy to understand how these thousands of lights in the sky have fascinated
and also intrigued humanity throughout its existence. The Sun, which was
worshiped by various religions and cultures over time and that in essence is
necessary t o all forms of life , and the Moon , governing the night sky while
continuously changing its phases, are the most visible object in the sky. When it
comes to the stars they seem to stay fixed in the sky, although it seems to be
rather an optical illusion. Th e planets, which are relatively bright objects, move
with respect to the stars around the Sun and around their axes.
The phenomena in the starry sky aroused people‟ interest since long time
ago. The Cro Magnon people made bone engravings 30 ,000 years ago, which
may depict the phases of the Moon. These discoveries took astronomy, as a
science, from the start of our civilization until today, to great heights. These
calendars, made in ancient times, are the oldest astronomical documents, 25,000
years older than the writing itself.
In order to get good crops and to have a more accurate prediction,
agriculture requires a good knowledge of the seasons, their dete rmination being
borne by Astronomy. Religious rituals and omens in ancient times, in different
cultures and religions that have existed over time, were and are based on the
location of celestial bodies, in the infinite universe of knowledge [1].

*E-mail: gabrielbadescu @yahoo.com

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Considerin g all the things mentioned above, the calculation of time became
increasingly more accurate, and people learned to calculate in advance the
movements of celestial bodies, drawing up calendars of various types, most of
which are influenced by the position o f the stars, the Sun and Moon and the
Earth's position in relation to them.
Over the centuries civilization has developed and part of its development
came from the maritime sector, especially when sea routes expanded and were
increasingly longer and ships travelled farther from their ports [2]. This issue,
namely the location of the ship, represented a big problem at a certain time.
Determining the position and distances thereof was a problem for which
astronomy provided a practical solution which then solv ed many other problems
over time, both in sea and land transport. Among other problems that Astronomy
solved or attempted to solve were those concerning navigation, which were its
most important tasks in the 17th and 18th centuries when the first accurate tables
were published on the movements of planets and other celestial phenomena
observed in the sky, only that now these observations were made with modern
tools of observation, measurement and determination. These developments were
made possible after the laws governing planet ary motions were discovered by
Copernicus, Tycho Brahe, Kepler, Galilei and Newton.
More than any other science, the research in the vast field of A stronomy
changed the way one sees the world, from geocentric and anthropocentric
conc epts to a modern point of view of a vast universe compared to which man
and Earth play an insignificant role. With the help of Astronomy people could
see and conceive the real scale of the nature surrounding us. Without it people
would not be able to compr ehend the infinite size of the U niverse of which they
are a part of.
Today, modern Astronomy is a fundamental science that has grown
because people have come to wonder how the planets move, where the Earth fits
in the universe, within our galaxy called the Milky Way and in our solar system,
motivated by human curiosity and the ancestral desire to know more about
nature and the Universe. Astronomy, together with Astrophysics and Geodesic
astronomy, has had and has a key role in the formation of a scientific picture of
the world in which we live and in which we operate daily, throughout the period
it has been perceived as a science. „A scientific view of the world‟ is a model of
the Universe based on astronomical observations, theories thoroughly tested in
time and a logical reasoning based on tried and tested formulas, tangible and
verifiable. In Astronomy, as in general, observations are always a final test of a
model created by man that meets reality in a greater or lesser extent. In reality, if
the astronom ical model which was designed is not consistent with observations –
in particular and in general – it must be changed, and this process should not be
limited by concepts or philosophical, political or religious beliefs, or otherwise.
Initially, the officia l position of the Church, as a representative of a new
religion and of the Romans, which expanded to the point of preval ence, was
quite cautious about S cience in general, simply because it was a product of the
ancient pagan world. With all these reasons fo r distrust and suspicion,

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257
Astronomy was essential, since a Church (religious) calendar had to be designed
to determine the holy days of Christians, especially the date of Easter. This was
a good reason why the g reat sages and bishops studied A stronomy and through
this knowledge they got closer to the cosmology and cosmogony of the Old
Testament. In fact, in order to reconcile the astronomical views of their time
with the cosmogony described in the Book of Genesis, they wrote treaties on the
six-day Creation (Peri Hexahemerou or On Hexameron), which became the short
spiritual texts of the 4th century AD [3, 4].
As Th. Nikolaidis writes, “the most important texts were the „Homilies
to the Six-day Creation‟ by Saint Basil the Great and those by his brother ,
Saint Gregory of Nyssa, treatises that exerted an especially strong
influence, not only in the East but also in the West ” [5].

2. Modern astronomy at short

Nowadays, modern A stronomy is exploring the whole U niverse and its
various forms of matter and energy through different branches within it, some of
which are: Geodetic Astronomy, Astrophysics, Astrometry, Stellar Astronomy,
Galactic Astronomy, Extragalactic Astronomy, Cosmology, Stellar Evolution,
Formation and Evolution of Galaxies, the Emergence and Evolution of the Solar
System, Star Formation, Planetary Science. Astronomers in general, through
various branches of astronomy, study the contents of the universe, starting with
elementary particles and molecules (with masses of 10-30 kg) to the largest
clusters of galaxies (with masses of 1050 kg).
Astronomy can be divided into different branches in several ways, as
shown above; also, another division can be made, depending on the research
methods or research objects of various aspects of the universe which are
investigated.
The Earth, the planet on which we live and conduct our daily activ ities, is
of great interest to A stronomy, for many reasons. The vast majority of
astronomical observations must be made through the atmosphere, and t he
phenomena of the upper atmosphere and magnetosphere reflect the state of the
interplanetary space at the time of observations. Among other aspects, the Earth
is therefore the most important object of comparison for planetary scientists in
the studies, t heories and models they design and must empirically verify.
The Earth‟s natural satellite, namely the Moon, is still studied by modern
astronomical methods, although in the last century, astronauts and spacecrafts
have visited its surface and brought samp les back to Earth. For the majority of
astronomers, but especially for amateurs, the Moon is an interesting object from
several points of view and is easily observed without tools or specialist
astronomical instruments.
In the study of planets in the S olar System, the situation in the 1980s was
the same as in the Moon‟s exploration 20 years earlier, i.e. in the early 1960s,
and a number of surfaces of planets and their satellites were mapped by
spacecraft or their satellites and space ships landed on Mars a nd Venus. This

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type of exploration added a lot to our knowledge of the conditions on other
planets. With all this, continuous monitoring of planets can only be done on
Earth, and many bodies in the solar system are still waiting for their space ship
in ord er to be explored and – why not – colonized in the near or distant future.
In the Milky Way Galaxy, of which we are a part, the Solar System is
ruled by the Sun, which produces energy in its core through nuclear fusion and
has temperatures of over 6,000 d egrees Kelvin. The Sun is the closest star to
Earth and as such, its study helps to understand the conditions on the other stars.
There are thousands of stars that can be seen with the naked eye, but even a
small telescope reveals millions of them. When us ing professional telescopes the
amount of stars is much higher. Stars that are subject to observation by
astronomers and other scientists can be classified according to the characteristics
observed. The majority of these stars are like the Sun, which is a medium sized
star, and we call them main sequence stars. However, some stars are much larger
(giant or supergiant stars), and some are much smaller (dwarf stars). Different
types of stars represent different stages of stellar evolution in the solar system
and the universe in general. Most stars are components of binary or multiple
systems; many are variables: their brilliance is not constant.
Nowadays, among the newest objects studied by astronomers, are
compact stars: they are represented by neutron stars and black holes. In these
compact stars, matter is so compressed and the gravitational field so powerful
that we use Einstein ‟s theory of relativity to describe matter and space.
As a representation and image, stars are like bright dots in a seemingly
empt y space, that is, nevertheless, part of the universe. However, interstellar
space is not empty but contains large clouds of atoms, molecules, elementary
particles and dust. An amount of new material is injected into interstellar space
by exploding stars th at erupt over time while in other places new stars are
formed by contracting interstellar clouds.
Most of the stars are not evenly distributed in space and in the universe,
but form concentrations, groups of stars. These consist of stars born near each
other, and in some cases, stars that remained together for billions of years, as if
completely ignoring time, which is relentless.
For an amateur or a professional carrying out observations with adequate
equipment or even with the naked eye, the highest conce ntration of stars in the
sky is the Milky Way, the galaxy to which we belong. The Milky Way is a
massive star system, a galaxy consisting of over 200 billion stars. All the stars
visible to the naked eye belong to the Milky Way. Light passes through our
galaxy in 100,000 years.
Our galaxy, namely the Milky Way, is not the only galaxy out there, but
one of countless other galaxies. Galaxies often form clusters of galaxies, and
these groups can be brought together in super -clusters of galaxies. Galaxies are
seen at all distances that can be observed by us, especially if we use high power
telescopes. In the most remote places we see quasars, knowing that the light of
more distant quasars that we see no w was in fact emitted when the U niverse was
a tenth of its p resent age.

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259
In Astronomy, the largest object studied by astronomers is represented by
everything that exists in the enti re Universe. In the beginning, C osmology was
reserved for philosophers and theologians and over time – especially today – has
become the subject of physical theories and concrete astronomical observations.
Among the many branches of research, spherical and positional,
astronomy studies the celestial sphere coordinate system, their changes and the
apparent position of celestial bodies in th e sky. Celestial mechanics studies the
motion of bodies in our solar system: stars systems, galaxies and clusters of
galaxies in the universe, which is infinite. Astrophysics deals with the physical
properties of celestial bodies, using methods of modern p hysics, combined with
new theories in various related fields. Astrophysics has a central p lace in almost
all branches of A stronomy, as it helps decipher and v erify the numerous theories
in Astronomy in general .

3. Earth seen from an astronomical and geodetic point of view

A position on the Earth is usually given by two spherical coordinates
(although in some calculations rectangular or other coordinates may be more
convenient). If necessary, a third coordinate, e. g. the distance from the centre can
also be used.
The reference plane is the equatorial plane , perpendicular to the rotation axis
and intersecting the surface of the Earth along the equator . Small circles parallel to
the equator are called parallels of latitude . Semicircles from pole to pole are
meridians . The geographical longitude is the angle between the meridian and the
zero meridian passing through Greenwich Observatory. We shall use positive
values for longitudes east of Greenwich and negative values west of Greenwich.
Sign convention, howeve r, varies, and negative longitudes are not used in maps; so
it is usually better to say explicitly whether the longitude is east or west of
Greenwich [6]. The latitude is usually supposed to mean the geographical latitude ,
which is the angle between the pl umb line and the equatorial plane. The latitude is
positive in the northern hemisphere and negative in the southern one. The
geographical latitude can be determined by astronomical observations [6].
The altitude of the celestial pole measured from the hori zon equals the
geographical latitude. (The celestial pole is the intersection of the rotation axis of
the Earth and the infinitely distant celestial sphere) [7-9].
Because the Earth is rotating, it is slightly flattened. The exact shape is rather
complicat ed, but for most purposes it can by approximated by an oblate spheroid,
the short axis of which coincides with the rotation axis. In 1979 the International
Union of Geodesy and Geophysics (IUGG) adopted the Geodetic Reference
System 1980 (GRS -80), which is used when global reference frames fixed to the
Earth are defined. The GRS -80 reference ellipsoid has the following dimensions:
equatorial radius a = 6,378,137 m,
polar radius b = 6,356,752 m,
flattening f = (a−b)/a = 1/298.25722210
The shape defin ed by the surface of the oceans, called the geoid , differs from

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this spheroid at most by about 100 m. The angle between the equator and the
normal to the ellipsoid approximating the true Earth is called the geodetic latitude .
Because the surface of a liqui d (like an ocean) is perpendicular to the plumb line,
the geodetic and geographical latitudes are practically the same.

4. The c elestial sphere used in Astronomy

When we look at the starry sky, it appears to us like a spherical cap that is
supported all around by the horizon and on which we can see the stars projected
according to the directions of the visual rays that are joined to the eye of the
person who makes the observation. The sphere that includes this cap was named
local celestial sphere, frequen tly called topocentric sphere or direction sphere in
astronomy.
Since the distances to the stars are great, constellations appear to us as
having the same geometric shape regardless of where we are on the globe or if
visibility is hindered by the horizon. Moreover, the same issue happens
regardless of the position of Earth in its orbit around the Sun, and regardless of
the calendar date on which the observations are carried out. We can generalize
that the observation directions of the stars remain parallel to each other at any
moment during the observation. In reality, we shall see that because of several
astronomical phenomena that are inevitable, the parallel nature of the visual
rays‟ directions to the stars is only an approximation, but one which has pr actical
utility.
Regarding the position of the stars and constellations, i.e. where they are
on the celestial sphere, this position is continuously changing due to the Earth's
rotation on its axis and its movement around the Sun. If we look at the stars on a
clear night we see stars that pop up and then go down and stars that remain
visible throughout the night. Another aspect is that an observer will also see that
there are stars that readily cross the sky and stars which are slowly moving on
the same sky. All changes in the position of the stars coming from daytime
motion are different for their observers who are in different places on the globe.
With this in mind it is possible to determine the position of the observer on
Earth, position expressed by the astronomical coordinates
( , )
of the vertical
of the place in the point it is located. The instruments used and the methods of
observation, measurement and determination of these coordinates are the subject
of practical G eodetic astr onomy.
These clarifications made before are very important because the position
of a star on the celestial sphere is given by the direction on which an observer
sees it, the distance to the star being negligible compared to its position. Most
times, in different situations, the radius of the celestial sphere can be considered
infinite, and in other cases we can consider the celestial sphere as a unit radius.
The ancient U niverse was confined within a finite spherical shell. The
stars were fixed to this shell and thus were all equidistant from the Earth, which
was at the centre of the spherical U niverse. This simple model is still in many
ways as useful as it was in antiquity: it helps us to easily understand the diurnal

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261
and annual motions of stars, and, more important, to predict these motions in a
relatively simple way. Therefore we will assume for the time being that all the
stars are located on the surface of an enormous sphere and that we are at its
centre. Because the radius of this celestial sphere is practically infinite, we can
neglect the effects due to the changing position of the observer, caused by the
rotation and orbital motion of the Earth.
Since the distances of the stars are ignored, we need only two coordinates
to specify their direction s. Each coordinate frame has some fixed reference
plane passing through the centre of the celestial sphere and dividing the sphere
into two hemispheres along a great circle.
One of the coordinates indicates the angular distance from this reference
plane. T here is exactly one great circle going through the object and
intersecting this plane perpendicularly; the second coordinate gives the angle
between that point of intersection and some fixed direction.

5. Coordinate systems used in Astronomy

The positio n of the stars in the sky is defined by spherical coordinates
calculated by astronomers from making observations, by means of specific
instruments, from fixed points, represented by astronomical observatories. These
coordinates are tabulated in the form of tables called „ephemerides ‟, annually
made available to users for different purposes. They are necessary for geodetic
astronomy work where, in order to determine the coordinates of the key points,
stars are considered fixed points (known coordinates), rel ative to the celestial
sphere (Table 1 ) [9, p. 55].

Table 1. Coordinate systems used in Astronomy.
Fundament
al reference
planes Polar axis of the
fundamental
planes Reference directions
(origin) in fundamental
planes Coordinate
system
the horizon
of the
location the vertical of
the location the intersection of the
horizon and meridian of
the location horizontal
coordinate
system
the celestial
equator Earth‟s axis the intersection of the
celestial equator and the
meridian of the location zones
coordinate
system
the intersection of the
celestial equator and the
celestial meridian of the
vernal equinox equatorial
coordinate
system
the ecliptic polar axis of the
ecliptic the intersection of the
ecliptic and the ecliptic
meridian of the vernal
point eclipt ic
coordinate
system

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There is the possibility of adopting several reference planes and thus we
can define various astronomical and geodetic coordinate systems, for example:
horizontal coordinate system, zones coordinate system, equatorial coordinate
system and ecliptic coordinate system.
In the following we will present, one at a time, these systems of
coordinates, determining for each the reference planes, type of coordinates, and
also specific characteristics (Table 1).
A coordinate system is generall y represented by three perpendicular axes
and is defined by origin, a fundamental reference plane (plane XY), a reference
direction in this plane (X -axis) and the positive part of this plane. One can use
other planes or fundamental directions: for example, the Z -axis direction (normal
to the plane XY), the pole of the XY plane or the X -axis can be defined as a line
of intersection of two planes of reference [7; 8; 9, p. 55].

Figure 1. Figure 2.
Rectangular coordi nate systems . Spherical coordinate systems .

Vector r from the origin to the object, also called position vector, can be
represented by its rectangular coordinates (x, y, z), the projections of vector r on
the three axes (Fig. 3.1). Also, the positi on vector r can be represented by
spherical coordinates (Fig. 3.2) in which direction is defined by the longitude
angle
in the reference plane XY and the latitude angle
in the reference
plane (sometim es the polar angle
090
or the complement of the latitude
angle are used; the prefix „co‟ can be added to the name, in this case –
colatitudine). These angles are called and have different symbols in the
coordinate systems specific t o astronomy. Geometric coordinate transformations
between different astronomical coordinate systems and correcting physical
effects can be made using the techniques of spherical trigonometry or vector and
matrix algebra [7, p. 38 ; 8, p. 23; 9, p. 55].

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263
The concept of celestial sphere is common for explanations, sphere arcs
representing the angl es between directions. The cent re of the sphere can be
positioned at various locations, but in most cases illustrates the origin of the
coordinate system (referenc e trihedral). Also, when an object represented on the
sphere changes its radial distance from the cent re of the coordinate system, these
changes need to be incorporated in the mathematical calculating models [7, p.
42; 8, p. 27 ; 9].

6. Conclusions

Astronomy is the science that has always fascinated personali ties in the
field of religion, P hilosophy and Science as well. Astronomy has solved a
number of problems that people have had ever since ancient times.
Religion needed Astronomy to clearly record the course of various
important days for religious holidays. During history Science needed Astronomy
to solve problems that had to be solved in scientific terms.
This paper presents Astronomy over time until today, finally presenting
the coordinate systems th at are indispensable to today‟s sciences: Space geodesy
(GPS), Geographic Information Systems (GIS) , sea, air and naval transportation,
astronautics and other fields.

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