Peruse previous posts here.
Let’s return to our original idea from part 1. When we draw the ecliptic (that line that the Sun appears to travel along) on the sky, we cut through several “constellations.” Well, this begs the question “What is a constellation?”
Casually speaking a constellation is a “group of stars.” (Technically speaking, the term constellation currently refers to an internationally agreed upon space boundary. But for now, let’s just talk about them in terms of star groupings.)
…and a “group” is just an idea. It is a projected connection made up in our minds. You guys know there are not actual strings tying the stars of a constellation together like pieces of cosmic caution tape, right? The constellations are the pictures that resulted from bored shepherds and lost sailors playing connect the dots on the sky.
Here’s a fun experiment. Take a sheet of paper and draw a bunch of dots all over it. Next, make a few photocopies of that sheet. Give your friends a copy with a pen and ask them without looking at their neighbor’s paper, to connect some of the dots to make a picture. Unless your friends are psychic twins, the results should be different.
Now, some of the stars in the sky are close together and make “obvious groups.” So, that your friends might trace out a similar configuration. The biggest difference in this case would be the interpretation. ”I see a swallow!” compared to “I see a pair of fish.”
But more of the groups are less obvious. The stars are blobbed on the sky in such a way that the demarcations have more possibilities. ”I see a giant scorpion with magnificent claws!” compared to “I see a set of scales. Oh, and a bug next to it.” One person sees one giant blob, another sees two smaller blobs.
Eventually for practical purposes, the shepherds, the sailors and other star gazers got together to agree on which pictures to use so they could share ideas about space, time, planetary motion and navigation more easily. Now since this was before the Internet, different groups of star gazers got together in different parts of the world and came up with different ideas. Different collections of agreed upon pictures were formed. The predominant collection of constellations used today comes down from the Greek retweaking of the Babylonian systems. The constellations most of us know are part of the Western sky culture.
But I digress… today’s main idea is that these star groups are arbitrary.
Hold onto that idea, come back tomorrow and I might make a point or two about something relevant to our original question.
You can also follow her on Twitter.