Milky Way facts

night Milky Way

• The Milky Way, is the galaxy in which the Solar System is located. It is a barred spiral galaxy that is part of the Local Group of galaxies.
• The stellar disk of the galaxy is of the size of about 100,000 light-years in diameter. It is around 1000 light-years in thickness. It consists of as many as 200 to 400 billion stars. It is nearly impossible to estimate the exact age of the Milky Way. However, the age of the oldest star in the Galaxy is about 13.2 billion years.
• Its name is a translation of the Latin Via Lactea, in turn translated from the Greek Γαλαξίας (Galaxias), referring to the pale band of light formed by stars in the galactic plane as seen from Earth.
• As seen from the Earth, the Milky Way appears as a hazy band of white light in the sky during the nights. It divides the night sky into two somewhat equal hemispheres.
• Some sources hold that, strictly speaking, the term Milky Way should refer exclusively to the band of light that the galaxy forms in the night sky, while the galaxy should receive the full name Milky Way Galaxy, or alternatively the Galaxy.
  
  
  
• The Galaxy is composed of a disk of gas, dust and stars that surround a bar-shaped region. The disk forms four arm structures that take a spiral shape.
• 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.
• The Milky Way appears brightest towards the constellation of Sagittarius.
• The Milky Way has a relatively low surface brightness due to the interstellar medium that fills the galactic disk, which prevents us from seeing the bright galactic center. It is thus difficult to see from any urban or suburban location suffering from light pollution.
• The mass of the Galaxy is estimated to be 5.8x1011 solar masses. Most of its mass is dark matter, a hypothetical matter that is not reactive towards electromagnetic force.
• The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the Solar System lies close to the galactic plane.
• The galactic center of the Milky Way is in the direction of Sagittarius. The galactic disk bulges outward at the galactic center. It has a diameter of a value between 70,000 to 100,000 light-years.
• The galactic plane is inclined by about 60 degrees to the ecliptic (the plane of the Earth's orbit).
• The Sun’s galactic motion is in the direction of star Vega and is tilted at an angle of 60 sky degrees to the galactic center. The Sun oscillates up and down relative to the galactic plane. For the solar system to complete one orbit around the galaxy, it takes as many as 225 to 250 million years! This time period is referred to as the galactic year.
• Observations presented in 2008 by Robert Benjamin of the University of Wisconsin-Whitewater suggest that the Milky Way possesses only two major stellar arms: the Perseus arm and the Scutum-Centaurus arm. The rest of the arms are minor or adjunct arms. This would mean that the Milky Way is similar in appearance to NGC 1365.
• Active star formation takes place in the galactic disk and in the high-density areas in the spiral arms.
• The Galaxy is believed to have four logarithmic spiral arms. They are named as Perseus Arm, the Scutum-Crux Arm, the Carina and Sagittarius arm and the Norma and Cygnus Arm. According to a recent discovery, there is an outer extension to the Cygnus Arm. The Orion Arm, which is a relatively smaller arm, contains our solar system.