The milky way

Milky Way Galaxy, large spiral system consisting of several hundred billion stars, one of which is the Sun. It takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky as seen from Earth. Although Earth lies well within the Milky Way Galaxy, astronomers do not have as complete an understanding of its nature as they do of some external star systems. The Milky Way is a disk that measures about 120,000 light years across, with a central bulge that has a diameter of about 12,000 light years. The disk is not perfectly flat though, it is warped due to the neighboring galaxies Large and Small Magellanic clouds. These two galaxies have been pulling on the matter in our galaxy.

Our galaxy is made up of about 90% dark matter, matter that cannot be seen, and about 10% “luminous matter”, or matter that we can see with our eyes. This large quantity of dark matter causes an invisible halo that has been demonstrated by simulations of how the Milky Way spins. If the dark matter did not exist then the stars within the Milky Way would orbit much slower than has been observed.

In order for the Milky Way to achieve its current size and shape it has consumed other galaxies throughout its history. Our galaxy is currently consuming the Canis Major Dwarf Galaxy by adding the smaller galaxy’s stars to its own spiral.

Like larger galaxies, the Milky Way has a super massive black hole at its center called Sagittarius A*. This black hole has an estimated diameter of 14 million miles, which does not include the disk of mass being drawn into it. This outer disk has about 14.6 million times the mass of our Sun in what would be similar to the orbit of the Earth.

About 10-15% of the Milky Way’s visible matter is made of dust and gas, with the rest being stars. The Milky Way is only a medium sized galaxy with an estimated 200 billion stars. The largest galaxy we know of is called IC 1101 and has over 100 trillion stars.

Although most stars in the Galaxy exist either as single stars like the Sun or as double stars, there are many noticeable groups and clusters of stars that contain tens to thousands of members. These objects can be divided into three types: globular clusters, open clusters, and stellar associations. They differ primarily in age and in the number of member stars.

Star clusters:

The largest and most massive are the globular clusters, so called because of their roughly spherical appearance. The Galaxy contains more than 150 globular clusters, although the exact number is uncertain.

Open clusters:

Clusters smaller and less massive than the globular clusters are found in the plane of the Galaxy intermixed with the majority of the system’s stars, including the Sun.

Stellar associations:

Even younger than open clusters, stellar associations are very loose groupings of young stars that share a common place and time of origin but that are not generally tied closely enough together gravitational to form a stable cluster.

Everything in space, including the Milky Way, is moving. The Earth moves around the Sun, the Sun moves in the Milky Way, and the Milky Way cruises through space. The orbital plane of the galaxy is rotating around its own axes, although the stars which are closer to the center of the galaxy have the same angler velocity as the stars which are far from the center of the galaxy. The Local Group of galaxies, which the Milky Way is part of, is estimated to be moving at about 600 km/s or 2.2 million km/hr.

Unfortunately Since we are located about 26,000 light years from the Milky Way’s center we cannot take pictures of the disk. Any representation that you have ever seen of our galaxy is either a different spiral galaxy or what an artist thinks it might look like.