Saturday, June 18, 2011


 A star is a luminous body which is seen projected onto the celestial sphere: they are stars, galaxies, planets, but in this last case shine with reflected light).
The means to investigate the stars is the electromagnetic radiation that bodies radiate light.

Electromagnetic radiation is a form of energy that propagates through space in waves that have different lengths and frequencies.

The shortest waves are the most energy and are the visible waves, x-rays, the rays of the ultraviolet.
The longer waves are less energetic and are the infrared and radio waves.
When radiation interacts with matter energy is absorbed into blocks called photons.
The waves in space are faced with the only atmosphere that is transparent to radio waves and optical waves, which are the only ones to arrive on the earth's surface.
The tools used to interpret these waves are the telescopes and radio telescopes.
To capture other issues you must exit from the atmosphere and use other tools.
Mounted on the telescope you can find a spectroscope, which splits light into different components and shows the spectrum of optical waves.
There are three types of spectra: those of continuous emission, those lines may be either emission or absorption.
The continuous emission spectra are typical of solids or liquids at high temperature and high pressure gaseous bodies. These emit continuous emission spectra ranging from less energetic waves (red) to higher energy (purple).
The spectra of emission lines are very rarefied gas. An analysis of the spectra can understand that each chemical element emits radiation only some values ​​with some energy.
The spectrum is so characteristic of the element and serves to recognize the element itself.
Spectra absorption lines are continuous spectra that lack of radiation. In fact, of rarefied gases are interposed between the body and the observer to selectively absorb certain wave lengths.
Depending on the gas shortage in the continuous spectrum certain wavelengths absorbed by the gas.
The same gas emits and absorbs more of the same elements.
The spectrum of the sun is similar to that of other stars and is continuous with respect to the nucleus that is formed by high-pressure gas, while the top is so rarefied and absorbs certain wavelengths.

The study of spectra is therefore dates to the chemical composition of the surface layer, but also the core, since we know that hydrogen is present, but also other groups of elements and molecules (OH) which give absorption bands.
The spectra of several stars are different from each other because it changes the temperature and hence the spectrum also gives information on surface temperature of the star.
A massive star has a higher temperature and takes on a white or light blue, a modest star reaches about 6000 ° K temperature, and is yellow, while the small stars can reach 3000 ° K and have red.
The spectra also give information on the movements of the stars, a movement that is divided into two movements: one on the celestial sphere and the observer along the line joining the observer abstraction.
For the observer moves with respect to the absorption lines can be moved toward the red or towards the violet. This phenomenon is linked to the Doppler effect that if the star is approaching you will have shorter wavelength and the phenomenon called blueshift, while if it goes away you have the phenomenon called red shift and the waves are longer.

Now the information about the movements of the stars are also from the study of neutrinos and gravitational waves.

The celestial sphere is an optical illusion, but is important because it can be placed on the stars.
The stars vary in brightness and color and have a pulsing aluco unlike planets that have a steady light.
The stars seem to be grouped into constellations, which are in turn an optical illusion. I'm not close to each other, but they are such because they are projected onto the celestial sphere.
88 constellations were established and then the celestial sphere is divided into 878 areas, each of which contains a constellation.

The names of the constellations are derived from mythology, or names of objects.
Within the constellation's brightest stars are, but it's apparent brightness depends only on the neighborhood.
The stars are called with the greek letters of the alphabet starting from A, as the brightest, most of the genitive of the constellation name.
Some stars have a name just like Sirius.

Over 50% of the stars is a binary system of two stars connected by the gravitational force.
To fix the position of a star on the celestial sphere is a reference system. One takes into account the observer's position, while one considers the land a point and is therefore an absolute system. The latter is formed by projecting the axis of the earth and making it the world axis, and extending to the equatorial plane of the celestial equator have a plan. So the grid is projected to have a geographical grid heaven.

As meridians and parallels are drawn. The parallel reference is the only celestial equator circle, while the meridians is considered vital to passing through the point g, the east, which is the point where the sun is the spring equinox and the point Mega opposite, the west, the position of the sun on the autumn equinox.
The sky coordinates are therefore the heavenly ascension declination line. The first is the angle that subtends the arc of the meridian and the equator of the star sky and can have values ​​between 0 and 90 in one hemisphere and the other between 0 and -90.
The right ascension is the angular distance instead of the meridian passing through the star and the reference meridian on the calculated parallel. The angle that is formed, said, is measured starting from the reference meridian counterclockwise and takes values ​​from 0 to 360. Often it is not in degrees but in hours and minutes.
If you take into account the position of the observer identifies the axis of the world the North Pole and the south celestial pole. The vertical line connecting the center of the observer on earth finds two points on the celestial sphere: the zenith and the nadir.

It then intersects the celestial sphere with a plane perpendicular to the plane of the observer and passing through the center of the earth and in heaven that identifies the horizon does not coincide with the equatorial plane unless the observer is not at the pole.

The two circles intersect at points east and west.
It then traces a circle passing through the zenith and the nadir is called the celestial meridian of the place and identify two intersections with the horizon sky called the north and south.
Are identified as horizontal or relative coordinates that are the height and azimuth.

The height is the height measurement of the star on the horizon, while the azimuth is the angle between the south and the vertical plane of the horizon of the star. It is measured in a clockwise direction and assumes all values ​​from 0 to 360.

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