Milky Way Viewing Season
"The Milky Way is nothing else but a mass of innumerable stars planted together in clusters."
~ Galileo Galilei, 1610
Our Milky Way is a barred spiral galaxy composed of an estimated 300 billion stars, along with dust, gas, and nebulae. Our Sun resides on the inner part of a minor arm called Orion. This cosmological tartan, represents our view of the Milky Way with the lighter bands showing the concentration of stars located in the direction of the galactic plane, and the darker regions representing the Zone of Avoidance, where the light is blocked by stars, light attenuation, and interstellar dust. The red lines represent the cosmological red shift due to the expansion of the universe. At least three types of redshift occur in the universe — from the universe's expansion, from the movement of galaxies relative to each other, and from "gravitational redshift," which happens when light is shifted due to the massive amount of matter inside of a galaxy. While galaxies such as our Milky Way are on the move, the impending collision between our Milky Way and fellow spiral galaxy Andromeda will occur about 4.5 billion years from now, so don't panic! 🌌
In western culture, the name "Milky Way" for our view of our own galaxy is derived from its appearance as a dim un-resolved "milky" glowing band arching across the night sky. The term is a translation of the Classical Latin via lactea, in turn derived from the Hellenistic Greek for "milky circle". In Greek mythology, the Milky Way was supposedly created from the forceful suckling of Heracles, when Hera acted as a wet nurse for the young hero.
From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. And until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Observations by Edwin Hubble showed that the Milky Way is just one of many galaxies - now estimated as hundreds of billions of galaxies in the observable universe.
This tartan, designed by Carol A.L. Martin, represents a view of the Milky Way with the light bands showing the concentration of stars located in the direction of the galactic plane along with the dark regions in the Zone of Avoidance where the light is blocked by interstellar dust. The red lines represent the cosmological red shift, due to the expansion of the universe.
Generally the dense part of the Milky Way is best viewed when it is as high as possible in the Southern sky. Facing south during April and May the pre-dawn hours are best. From June to early August the best time is near midnight, though the Milky Way will be visible almost all night. From Mid August through September the best time is soon after the sun has set and the sky has grown dark. The farther North you go, the lower in the southern sky the Milky Way will be. If you live above 65 degrees north, you will never see the Milky Way core because it never rises above your local horizon.
For details on this latest announcement of an X-shaped formation within our galaxy, click the "Nature Speaks" photo by Michael Shainblum.