COURSE Introduction to Astronomy (46) double and multiple stars.
Many stars like Aldebaran, Antares, Rigel, Polaris, etc at first glance appear as a single point of light, observed telecospio are formed by two or more stars next to each other. These stars are called double if two triples if they are three, and if more, they are called, in general, multiple.
double stars are divided into:
1) optical Doubles: When are composed of two stars located far distiancia independently of one another and who are next projected on the celestial sphere by the effect of perspective.
2) physical or binary Doubles: When between the two stars there is physical linkage, that is, they spin around each other under the laws of Kepler and Newton, forming a binary system.
In some double stars, the components are so close that even with the most powerful telescopes they appear as single stars and are known to be double by spectral analysis, or by the darker eclipses of the components produced wholly or partly the brighter the star appear as a variable, such as the star Agol. Among the stars
triples have to Regulus, including Lyra multiple.
COURSE Introduction to Astronomy (45) Variable stars
A large number of stars will not shine steadily, but will vary periodically, or whatever it is, do not retain the same apparent magnitude and in a shorter or longer period and more or less regular, their magnitudes reach different values, such stars are called variables.
For example, the star Mira Ceti (constellation of the whale), which historically was the first known variable star in a period of 332 days passed from 2 nd to 9 th magnitude.
With the use of photography in astronomy, he discovered so much better the variability of the stars, so it was photographed the same region of sky in two different dates with the same instrument and in identical positions, comparing the two pictures can be seen if the stellar image varies or not.
Variable stars are classified as:
1) Intrinsic: those in which their magnitude variations due to changes in the star's internal structure, and that changes color, temperature and range, along with these changes of light .
2) Extrinsic: not regarded as real variables, since variability of sun light is produced by external physical causes unrelated to the star itself. According
cuva variability of the stars, they are divided into:
1) Periodic or regular: the light curve is periodic, ie, after an interval of time, called period, plays unalterably.
2) semiregular: ligeramnete period is variable and the curve is reproduced with low accuracy in each period.
3) Irregular: in these there is only one small indication of periodicity.
Observing variable stars is one of the most interesting work programs for the amateur astronomer. NO requeire costososy use of instruments made, and often most suitable for visual observation using binoculars or a 60 mm refractor. The work of variability is to define the range of variation of brightness and the period of the variable in question. For those observers who want to delve into this area to get in touch with major international organizations variable stars, and that through their newsletters, online via email or we can read the latest news that most interest us. These organizations also distribute some star charts to find the variable to consider, among other important features
COURSE Introduction to Astronomy (44) STELLAR MAGNITUDE (2)
The absolute magnitude of a star is the magnitude I would have said star if it were located at a distance of 10 parsec (1 parsec is 3.2616 years = 3.0857 X10 light 16 m, ie the distance from which Earth and the Sun would seem to be separated by an angle of 1 arc second) .
The magnitude of the stars is now known through the photometers or photographically.
is the term applied to the first magnitude stars that range from + 0.6 to 1.5, the second magnitude of the stars of + 1.6 to + 2.5; third magnitude from + 2.6 to + 3.5, etc.
The number of stars visible to the naked eye is about 6,500, with 20 stars of 1 magnitude, about 60 of 2 nd magnitude star close to 200 3 rd magnitude approximately 600 4 th magnitude, about 1,600 stars 5 ยบ size and more than 4000 of 6 th magnitude. Assuming that the stars are distributed equally in the sky, an observer in an instant see about 3,000 stars.
