Astronomy:

Stars

What’s a Star ??

Man has always lifted his head towards the black sky to observe it it was always fascinated by the stars that shine above him First he considered that stars were just spots that shone in the sky and were almost essential to the navigation… but When he discover the telescope the open view change and men know what means a star ! ( suns )

So why Do the stars shine? and how can it help us to navigate in the huge seas?

The Picture Bellow represent a night dark sky full of stars

The Definition of a Star

A star is a massive, luminous sphere of plasma Held together by gravity. The nearest star to Earth is the Sun, Which is the source of MOST of the energy on the planet. Some other stars are visible from Earth falling on the night When They are not obscured by atmospheric phenomena, Appearing as a multitude of fixed luminous point Because of Their immense distance. Historically, The most prominent stars on the celestial sphere Were grouped together into constellations and asterisms, and the brightest stars Gained proper names. Extensive catalogs of stars Have Been assembled by astronomers, Which Provide STANDARDIZED star designations.

Constellation

In modern astronomy, a constellation is an Internationally Defined area of the celestial sphere. These are grouped around asterisms Areas (Themselves Which are Generally Referred to in non-technical language as "constellations") Which patterns are Formed by prominent stars Within apparent proximity to one another on Earth's night sky.

Constellation Of Orion

Constellation of Lion

Constellation of the fish

Constellation of the Draco

Chapter 2

The Formation of Star (!)

Différent Stars in diffrent ages

The Birth Of a Star

Star formation

Star formation is the process by which dense regions within molecular clouds in interstellar space, commonly referred to as "stellar nurseries", collapse into spheres of plasma to form stars. As a branch of astronomy, star formation includes the study of the interstellar medium and giant molecular clouds (GMC) as precursors to the star formation process, and the study of young stellar objects and planet formation as its immediate products. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function.

Nebulas the nursuries of the formation of stars

Orion Nebula

Nebula of the Eye Cat

Nebula of the fox

The life of a star

The End of a Star

How it Becomes When it’s not a massive Star

Characteristics of a star

• Age :Most stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.8 billion years old—the observed age of the universe. The oldest star yet discovered, HE 1523-0901, is an estimated 13.2 billion years old.

• Chemical composition : When stars form in the present Milky Way galaxy they are composed of about 71% hydrogen and 27% helium,

• Magnetic field: The magnetic field of a star is generated within regions of the interior where convective circulation occurs. This movement of conductive plasma functions like a dynamo, generating magnetic fields that extend throughout the star.

• ClassificationSurface Different Stellar Classes[134]ClassTemperatureSample starO33,000 K or moreZeta OphiuchiB10,500–30,000 KRigelA7,500–10,000 KAltairF6,000–7,200 KProcyon AG5,500–6,000 KSunK4,000–5,250 KEpsilon IndiM2,600–3,850 KProxima CentauriMain article: Stellar classification

The Sun Composition

Conclusion

• Thanks For being With till now