How much do you know about galaxies? Did you know that planet Earth, as well as the entire Solar System, is found in the Milky Way galaxy? Let’s dig in and find out more.
By the end of this topic, you are expected to:
The Milky Way refers to the galaxy containing the Solar System, with the name referring to the appearance of the galaxy from the earth. It is a hazy band of light that is seen in the night sky formed from the stars that cannot be individually distinguished through the naked eye.
The Milky Way appears as a band from earth because its disc-shaped structure is viewed from within. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the universe. However, after 1920, observations by Edwin Hubble showed that the Milky Way was just one of the many galaxies.
The Milky Way is a barred spiral galaxy having a diameter between 150 000 and 200 000 light-years. It is estimated that this galaxy contains between 100 and 400 billion stars and more than 100 billion planets. The location of the solar system is at a radius of about 27 000 light-years from the Galactic Center. The galactic center refers to an intense radio source that is assumed to be a supermassive black hole called the Sagittarius A*.
Gases and stars at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant speed of rotation contradicts the laws of Keplerian dynamics and suggests that much of the Milky Way’s mass is invisible to telescopes, neither absorbing nor emitting electromagnetic radiation. This conjectural mass is referred to as dark matter. The period of rotation is approximately 240 million years at the radius of the sun. The Milky Way as a whole is moving at a velocity of about 600 km per second. The oldest stars in the Milky Way are nearly as old as the universe and therefore probably formed after the Dark Ages of the Big Bang.
The Milky Way has several satellite galaxies and it is part of the local group of galaxies, forming part of the Virgo Supercluster, which itself is a component of the Laniakea Supercluster.
The Milky Way is the second-largest galaxy in the Local Group, with its stellar disk said to be approximately 100, 000 light-years in diameter. This galaxy is approximately 1.5 trillion times the mass of the sun.
The Milky Way is visible from planet earth as a hazy band of white light, some 30⁰ wide, and arching across the night sky. However, all that the naked eye can see is the stars that are part of the Milky Way. The light comes from the accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions in the Milky Way “band” like the Coalsack and the Great Rift, which are areas where interstellar dust blocks light from distant stars. The Zone of Avoidance is the name given to the area of the sky that is obscured by the Milky Way.
The Milky Way contains between 200 and 400 billion stars and at least 100 billion planets. Perhaps, the Milky Way may contain ten billion white dwarfs, a billion neutron stars, and a hundred million stellar black holes.
