Milky Way Galaxy

The Milky Way Galaxy, also known as the Milky Way or the Galaxy, is a galaxy which contains the Solar System in which Earth exists. The Milky Way is classified by astronomers as a “barred spiral galaxy” and is located within a group of other galaxies called a Local Group of galaxies. While the Milky Way is large, to give an idea in relative terms, the Milky Way is just one of billions of galaxies that have been observed by scientists and astronomers. Technically, many people believe that the term “Milky Way” should be used to describe the band of light that the galaxy creates in the night sky, as opposed to the term “Milky Way Galaxy”, which should be used to refer to the galaxy itself.

The Milky Way Galaxy from Earth:
From Earth, the view of the Milky Way Galaxy shows a hazard white band of light which arches across the celestial sphere. The pale light from the Milky Way is caused by a group of stars and other material that is contained within the galaxy body. Judging locations of it is easy when observed in relation to a constellation. The Milky Way Galaxy looks brightest when observed from the direction of the constellation of Sagittarius when looking into the center of it. It spreads further north to the constellation of Cassiopeia and south to the constellation of Crux. The fact that the Milky Way appears to divide the night sky into two separate hemispheres indicates that the solar system that contains Earth is located very close to the galactic plane.

In urban areas and even suburban areas, it is extremely difficult to see the Milky Way because of its very low surface brightness. The reason for the low surface brightness is due to the interstellar medium, which in turn makes it extremely difficult to see the bright galactic center of it.

Characteristics of the Milky Way:
The “stellar disk” of the Milky Way Galaxy is about 100,000 light years in diameter and is about 1,000 light years thick. Astronomers believe that the galaxy is home to approximately 200 to 400 billion stars. The reason why scientists are unsure of the exact number is because of the large amount of low-mass stars, which are sometimes not classified as stars at all. This may seem like a lot of stars, but speaking once again relative terms, the neighboring galaxy, Andromeda, trumps the Milky Way, and has about one trillion stars. The distance between stars increases as one would travel further from the center of the galaxy. The surrounding area of the stellar disk contains a thick band of gas which is estimated to have a thickness of about 12,000 light years. In addition, many recent observations proves that the Milky Way is much larger than previously thought and may be similar in size to Andromeda.

Constellations

Constellations are used in modern astronomy to internationally define an area of the celestial sphere, which is an imaginary sphere concentric with Earth and rotating on the same axis as Earth. Traditionally, the term constellations refers to a pattern that is formed when imaginary lines are drawn in between stars close in proximity, forming an image. It is a tool to remember and identify stars which is still in use today. Overall, a constellation is any celestial bodies that appear in the sky to form a pattern. The main difference between constellations in the traditional sense and constellations of modern astronomy is that traditional constellations are patterns that appear identical to objects; while modern constellations are based on grid segments on the celestial sphere and are not based on patterns.

Star-patterns that have been discovered but have not been officially identified as constellations are called asterisms. The most famous example of an asterism is the big dipper, a constellation that is quite common and is even featured on the Alaskan state flag. The reason why it is not a true constellation is because it is part of a larger constellation called Ursa Major. Constellations that have been officially identified are identified by the International Astronomical Union (IAU).

The celestial sphere was officially divided into 88 separate constellations by Eugène Delporte in 1922. Famous Roman constellations, such as Orion, Leo and Scorpius were preserved with their root names intact during this official process. These older constellations were very important to ancient civilizations because they provided a navigation tool for travelers before the invention of the compass (this was during the Age of Discovery).

Actual Proximity of Stars in Constellations:
The stars that are contained within a constellation almost always have no relation to each other in astrophysical terms. When viewed from Earth, however, they appear to be very close to one another. In actuality, stars within the same constellations typically reside many light years apart from each other. The only exception to this notion is the constellation, Ursa Major, which has stars that do lie relatively close to one another.

What is a Star Chart?
A map recorded of the night sky is called a star chart. Since a star chart may be confusing to read, it is simplified by adding grids. The main purpose of using star charts is to locate known astronomical objects, such as stars, planets, galaxies and constellations. A star chart can also be used as a tool for navigation purposes.

The earliest known star chart was carved into the Mammoth tusk, a 32,500 year old diagram discovered in 1972. Thousands of years later, western civilizations began to draw more accurate and complete star charts. During the Age of Discovery, an age known for its significant discoveries from world exploration, the expeditions led to the finding of new constellations. The first significant star chart from this age was the globe of Jodocus Honius, which added twelve new southern constellations.