What Is The Milky Way

What is the Milky Way? Well, it is the name of the barred spiral galaxy in which our solar system is located. The Milky Way is part of the Local Group of galaxies. This group consists of about 30 galaxies with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. The galaxies of the Local Group cover a 10 million light year diameter and have a dumbbell shape. Its name is a translation of the Latin Via Lactea which in turn was translated from the Greek for Galaxias, referring to the pale band of light formed by stars in the galactic plane as seen from Earth.

The Milky Way, when viewed from Earth’s position in a spur of one of the galaxy’s spiral arms, appears as a hazy band of white light in the night sky arching across the celestial sphere. The plane of the Milky Way is inclined by about 60° to the ecliptic. The Galactic North Pole is situated at right ascension 12h 49m, declinations +27.4° near beta Comae Berenices. The Galactic South Pole is near alpha Sculptoris. The center of the galaxy is in the direction of Sagittarius. The Milky Way passes through Scorpius, Ara, Norma, and wraps up back in Saggitarius. The Milky Way looks brightest toward the galactic center, in the direction of Sagittarius. The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the Solar System lies near the galactic plane. The Milky Way has a relatively low surface brightness due to the gases and dust that fills the galactic disk. That prevents us from seeing the bright galactic center. It is difficult to see from bright urban or suburban areas because of light pollution.

The Milky Way Galaxy is approximately 100,000 light years in diameter, and is widely believed to be 1,000 light years thick on average. Many believe the galaxy to contain between 200 billion and 400 billion stars. The exact figure depends on the number of very low-mass stars, which is highly uncertain. This can be compared to the one trillion stars in the Andromeda Galaxy. The stellar disc does not have a well defined edge, instead, the number of stars drops exponentially with distance from the center of the Galaxy. Beyond a radius of roughly 40,000 light years the number of stars drops much faster with radius, for reasons that are not currently known to science. The Milky Way’s stellar disc is accompanied by a gaseous disc that is 12,000 light years thick.

The age of the oldest star discovered so far in the Milky Way, HE 1523-0901, is estimated to be about 13.2 billion years. That is about the same age as the galaxy. The age estimate was determined using the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure the beryllium content of two stars in globular cluster NGC 6397. It was determined that the elapsed time between the rise of the first generation of stars in the Milky Way and the first generation of stars in the cluster was between 200 and 300 million years. By including the estimated age of the stars in the globular cluster, 13.4 billion years, the estimated age of the oldest stars in the Milky Way is 13.6 billion years.

Here is a link to a good article about the Milky Way. Here on Universe Today we have a great article full of Milky Way facts. Astronomy Cast offers a good podcast about the large scale make-up of the universe.

Source: NASA

Tagged as: what is the milky way