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‘’my goal is simple: the complete understanding of the Universe” Steven Hawking

INDEX 1-. Birth 2-. Composition 3-. Kinds of stars 4-. Supernovas 5-. Why stars twinkle? 6-. Constellations 7-. Distances 8-. Bibliography and webgraphy

1-. Birth Their birthplaces are huge and could clouds formed by gas and dust, known as “nebula�. These clouds begins to shrink under by its own gravity. As a cloud loses size, it is broken into smaller groups. Each fragment may eventually become so hot and dense that a nuclear reaction begins. When the temperature reaches 10 million degrees, the fragment becomes a new star. After birth, most of the new stars is located in the center of a flat disk of gas and dust. Much of the gas and dust ends up being swept away by stellar radiation. However, before this happens, planets may form around the central star.

2-.Composition The compositions of stars are determined through spectroscopy. Spectroscopy is the study of something using spectra. Recall from the Electromagnetic Radiation chapter that a spectrum is what results when you spread starlight out into its individual colors. By noting what absorption lines (or sometimes, emission lines) are present and their strengths, you can find out a tremendous amount of information. Stars have absorption lines patterns similar to the Sun. This means that they are composed mostly of hydrogen and helium with traces of other elements.

3-.KINDS OF STARS There are some difference in terms of color when you look up at the night sky. But they are all basically the same, big balls of gas burning up to billions of light years away, right? Well, not exactly. In truth, stars are about as diverse as anything else in our Universe falling into one of many different classifications based on its defining characteristics.

4-. SUPERNOVAS One of the largest and rarest spectacles of the sky is a supernova explosion, which betrays the death of a star with mass old. An explosion that occurs on average every few hundred years, when the inner state of a supergiant suddenly becomes so unstable that the star explodes violently launched into space a cloud of fast movement. In the following weeks, the supernova emits a lot of radiation, sometimes as much as the rest of the galaxy to which it belongs.

During maximum brightness, the total equivalent radiant energies produced by supernovae may briefly outshine an entire output of a typical galaxy and emit energies equal to that created over the lifetime of any s​ olar-like​ star.​[4]​ Such extreme catastrophes may also expel much, if not all, of its stellar material away from the star,​[5]​ at velocities up to 30,000 km/s or 10% of the ​speed of light​. This drives an expanding and fast-moving s​ hock wave​[6]​ into the surrounding interstellar medium​, and in turn, sweeping up an expanding shell of gas and dust, which ​ observed as a supernova remnant.

5-. why stars twinkle? The stars, planets, even the Sun and Moon twinkle, all in varying amounts. Anything outside the atmosphere is going to twinkle. If you’re feeling a little silly using the word twinkle over and over again, we can also use the scientific term: astronomical scintillation. You can’t feel it, but you’re carrying the entire weight of the atmosphere on your shoulders. Every single square inch of your skin is getting pushed by 15 pounds of pressure. And even though astronomers need our atmosphere to survive, it still drives them crazy. As it makes objects in space so much harder to see. Stars twinkle, ​ , because as light passes down through a volume of air, turbulence in the Earth’s atmosphere refracts light differently from moment to moment. From our perspective, the light from a star will appear in one location, then milliseconds later, it’ll be distorted to a different spot. So why do stars appear to twinkle, while planets don’t? Stars appear as a single point in the sky, because of the great distance between us and them. This single point can be highly affected by atmospheric turbulence.

6-. CONSTELLATIONS A constellation is formally defined as a region of the celestial sphere, with boundaries laid down by the International Astronomical Union (IAU). The constellation areas mostly had their origins in Western-traditional patterns of stars from which the constellations take their names. The following lists of constellations are available: ● Modern constellations - a list of the current constellations. ● Former con​stellations​ - a list of former constellations. ● Chinese constellations - traditional Chinese astronomy constellations. ● List of Nakshatras - sectors along the moon's ecliptic.

7-. DISTANCES This list contains all known stars and brown dwarfs at a distance of up to 5 parsecs (16.3 light-years​) from the ​Solar System​. In addition to the Solar System, there are another 56 ​stellar systems currently known lying within this distance. These systems contain a total of 60 hydrogen-fusing ​stars (of which 50 are ​red dwarfs​), 13 ​brown dwarfs​, and 4 ​white dwarfs​. Despite the relative proximity of these objects to Earth, only nine of them have an ​apparent magnitude less than 6.5, which means only about 12% of these objects can be observed with the ​naked eye​.Besides the Sun, only three are ​first-magnitude stars​: ​Alpha Centauri​, ​Sirius​, and ​Procyon​. All of these objects are located in the ​Local Bubble​, a region within the ​Orion–Cygnus Arm of the ​Milky Way​. The image on the preceding page was created to demonstrate that Alpha Centauri is not a ​star​, but really a star system. Of the three stars in the system, the dimmest called Proxima Centauri - is actually the nearest star to the Earth. The two bright stars, called Alpha Centauri A and B form a close binary system; they are separated by only 23 times the Earth - Sun distance. This is slightly greater than the distance between Uranus and the Sun.

8-. Bibliography and webgraphy ● ● html ● -is-a-supernova.html ● d=15C9FE66B85CA1B653CCB5C4E837EDE09A7F3D22&selectedIndex=14&ccid= NNQ2o%2fvK&simid=607988403335137240&thid=OIP.M34d436a3fbca703b48 b5eccc7b2e5f88H0&ajaxhist=0

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