The M i lky Way

1. The Milky Way By: Padurariu Cristian Danciu Serban Padurariu Cristian & Danciu Serban

2. The Milky Way galaxy • Milky Way Galaxy, commonly referred to as just the Milky Way, or sometimes simply as the Galaxy, is the galaxy in which our Solar System is located. The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. Padurariu Cristian & Danciu Serban

3. Appearance from Earth • All the stars that the eye can distinguish in the night sky are part of the Milky Way Galaxy, but aside from these relatively nearby stars, the galaxy appears as a hazy band of white light arching around the entire celestial sphere. Padurariu Cristian & Danciu Serban

4. Size • The stellar disk of the Milky Way Galaxy is approximately 100,000 light-years (30 kiloparsecs, 9×1017 km) in diameter. It is estimated to contain at least 200 billion starsand possibly up to 400 billion stars,the exact figure depending on the number of very low-mass, or dwarf stars, which are hard to detect. Padurariu Cristian & Danciu Serban

5. Age • In 2007, a star in the Galactic halo was estimated to be about 13.2 billion years old, nearly as old as the Universe. As the oldest known object in the Milky Way at that time, it placed a lower limit on the age of the Milky Way. Padurariu Cristian & Danciu Serban

6. Composition and structure • The galaxy consists of a bar-shaped core region surrounded by a disk of gas, dust and stars forming four distinct arm structures spiralling outward in a logarithmic spiral shape (see Spiral arms). Padurariu Cristian & Danciu Serban

7. Galactic Center • The galactic disc, which bulges outward at the galactic center, has a diameter of between 70,000 and 100,000 light-years. The exact distance from the Sun to the galactic center is actively debated. Padurariu Cristian & Danciu Serban

8. Sun's location and neighborhood • The Sun (and therefore the Earth and the Solar System) may be found close to the inner rim of the galaxy's Orion Arm, in the Local Fluff inside the Local Bubble, and in the Gould Belt, at a distance of 7.62±0.32 kpc (~25,000±1,000 ly) from the Galactic Center. Padurariu Cristian & Danciu Serban

9. It takes the Solar System about 225–250 million years to complete one orbit of the galaxy (a galactic year),so it is thought to have completed 20–25 orbits during the lifetime of the Sun and 1/1250 of a revolution since the origin of humans. Padurariu Cristian & Danciu Serban

10. Environment • The Milky Way and the Andromeda Galaxy are a binary system of giant spiral galaxies belonging to a group of 50 closely bound galaxies known as the Local Group, itself being part of the Virgo Supercluster. Padurariu Cristian & Danciu Serban

11. Velocity • In the general sense, the absolute velocity of any object through space is not a meaningful question according to Einstein's special theory of relativity, which declares that there is no "preferred" inertial frame of reference in space with which to compare the object's motion. Padurariu Cristian & Danciu Serban

12. Discovery • As Aristotle (384-322 BC) informs us in Meteorologica (DK 59 A80), the Greek philosophers Anaxagoras (ca. 500–428 BC) and Democritus (450–370 BC) proposed the Milky Way might consist of distant stars. Padurariu Cristian & Danciu Serban

13. Milky Way vs. Andromeda • Our galaxy, the Milky Way, will collide with another galaxy, called Andromeda. • Although they are close on the scale of the galaxies they are yet far away as even light takes two million years to journey between them. Read more about >> Padurariu Cristian & Danciu Serban