Each star plus its planets, satellites moving around
planets, comets, and smaller heavenly bodies produce a
complex that is called “Planetary System”.
The name of this system derives from central star,
like solar system.
Celestial sphere
Imaginary sphere of the heavens, with the Earth at its
center. The sphere forms the basis for the coordinate
systems used in assigning positions to objects
observed in the sky. The equatorial system of
coordinates establishes a grid in the celestial sphere
that is based on the Earth's equator and poles,
projected outwards to intersect with the sphere.
Ecliptic
Ecliptic, in astronomy, is the apparent great-circle
annual path of the sun in the celestial sphere, as
seen from the Earth.
Zodiac
Zodiac, imaginary belt in the celestial sphere, is
extending about 17° on either side of the ecliptic,
the apparent path of the Sun among the stars.
Constellations: in astronomy, are any of 88 imagined
groupings of bright stars that appear on the celestial
sphere and that are named after mythological figures,
animals, or objects. The term also refers to the
delimited areas on the celestial sphere that contain
the named groups of stars. Some of these
constellations are; Ursa Major (Great Bear), Ursa
Minor (Little Bear), Scorpion, etc.
To facilitate the determination of heavenly bodies of
a constellation, each of them is called by Greek
alphabet. For example, the brightest heavenly body is
called “a”, and masses bearing less
luminosity are called “B”,
“γ”,etc. The brightest star in the
constellation of Ursa Minor is “Polaris”
located closest to the point toward which the axis of
the Earth is directed, thus roughly marking the
location of the north celestial pole.
Novas (1)
The term “Nova” has a Latin root (Latin
nova stella, “new star”). Nova is a term
that used for explosion on a star that makes the star
increase rapidly in brightness. Sometimes, this
brightness increase does not seem very strong. From
ancient times, human being watched the sky for hours
and hours to discover its mysteries out of curiosity.
Man gradually became relatively familiar with the
location of celestial bodies. This matter is
available in many cultures. The occurrence of sudden
events, such as comets, meteorites and novas commence
a new chapter in legends regarding good and bad omens.
The Chinese followed these events very carefully.
The oldest report is about recording of a nova in
134B.C. Occurrence of 160 novas reported from 134B.C.
to 1900. With regard to the improvement in optical
techniques and later organized plannings, these
figures increased within previous century.
Novas are known by their spectra and luminosity.
Their brightness may vary between 8-15. Novas belong
to a group of variable stars under the name of
“Cataclysmic Variable Stars”or
“CVs”. In this group of variable stars,
eruptions originate from nuclear processes of
nova’s superficial layers or in the deeper parts
of supernovas. In an outburst of nova, two main
components are observed bearing a frequency of 0.05 to
230 days. The main component is White Dwarf and the
second component is a Sun-like star. The mass
transference from the Sun-like star to the surface of
White Dwarf commences by changement of this system. A
disc-like shape appears around White Dwarf. The dense
White Dwarf produces a strong gravitational force.
With continuation of mass transference process, layers
locate on each other. Therefore, lower layers are
compressed more. Then, the required conditions for
commencement of nuclear processes in the surface of
White Dwarf is established. The beginning of this
process is eruption of star’s outer layers to
the space. Parallel to this situation, the luminosity
of star is increased. Different processes produce
eruptions in various types of CVs.
Novas based on their behavior produce three types;
Fast novas (NA), slow nova (NB) and very slow nova
(NC).
Fast novas
Fast novas reach their maximum luminosity, quickly and
remain at this level for several days. Then their
brightness decreases and may become flat. Parallel to
this decrement of luminosity, certain oscillations may
occur. Normally, star’s brightness reaches 3
degrees below the maximum level within 100 days or
less.
The light-graph of Nova GK Persei is as follows;
[Location of the graph]
Slow novas
These types of novas indicate an increase in
luminosity up to their maximum level. They remain at
this level from a couple of weeks to several months.
At the beginning, they indicate decrement of
brightness plus slight oscillations. But, its
luminosity increases, then it decreases indicating
slight increment reaches the second maximum. Next, it
reaches to a minimum. This decrement level is 3
degrees.
Very slow novas
Small group of novas are available that have
light-graphs similar to the previous cases. However,
they can remain in maximum level from a couple of
years to a decade. They decrease their luminosity,
slowly.
The list of recently discovered novas is as follows
(in terms of priority);
*Nova FH Serpentis 1970
*Nova V1500 Cygni 1975
*Nova NQ Vulpeculae 1976
*Nova PU Vulpeculae 1979
*Nova PW Vulpeculae 1984 No1
*Nova OS Andromedae 1986
*Nova V838 Herculis 1991
*Nova V1974 Cygni 1974
*Nova V4362 Sagittarii 1994 No1
*Nova V723 Cas 1995
In this part two examples from the above-mentioned
list are described; Nova V838 Herculis 1991 and Nova
V1500 Cygni
1975.
