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.