The Milky Way

At night, glancing up to the sky, it is possible to admire a milky white stripe through the vault of heaven. It really seems made with milk, causing the ancient Greek definition “Galaxia”, that exactly means “made with milk”.
The Galaxy or Milky way is a large, barred spiral galaxy with arms surrounding its bulge, a central swelling with a depth of about 16.000 light years. This bulge is placed in the middle of a disc that, in turn, contains the spiral arms, the gas filaments and stars extended from the centre of the disc, wrapping themselves up it. The disc is surrounded by an almost spherical halo extended until a 150.000 light years diameter, hosting about 200 globular clusters. They are spherical groups, extended for few hundreds of light years, able to contain a million of stars. In our galaxy, we found three arms: the Orion one, that contains the Sun (placed at about 28.000 light years from the centre), the Perseus and Sagittarius ones. In the middle of the bulge we have the nucleus, made of stars and stellar clusters, whose birth seems to date back to the formation of our galaxy.
The disc is largely composed by dust, interstellar gas and bright blue stars, recently born. These stars are placed, starting from the nucleus, along a spiral trajectory.
Our galaxy is not fixed in the Universe. Its spiral arms, in fact, orbit around the nucleus with different velocities. All the stars are trailed from this movement, like the Sun with all the Solar System, on an elliptical trajectory around the galactic centre, with a period of 250 millions of years and a speed of about 250 km/sec.

Special reports

From the Multimedia section

  • space

    Virgo cluster

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    space

    The Hercules Globular Cluster (M13)

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    space

    Mice Galaxies

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  • space

    The Pleiades

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    space

    Quasar

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    Cosmic radiation

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  • space

    Recession velocity and distance

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    Black hole

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    The flux of cosmic ray particles

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  • space

    Virgo cluster

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  • space

    The Hercules Globular Cluster (M13)

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  • space

    Mice Galaxies

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