From our Other Members...

The Sky Above

So you ‘ re interested in astronomy ( the study of the cosmos) and you’d like to learn more about the night sky. Let’s start by dividing the celestial sphere (the visible universe) into segments or regions. This has already been done for us by the International Astronomical Union (IAU). There is a finite number of eighty-eight regions (constellations) that cover our visible universe from earth. That’s not such a big number and it gets even smaller if you live in the northern hemisphere because there are quite a few constellations that are not visible to us from here. Let us focus on a very important group.

Many people say to me, especially at public star parties that they don’t know any constellations except the BIG DIPPER ( Ursa Major) and ORION. My reply is usually “ Everybody has heard of the ZODIAC and its twelve constellations.”

Now a little ‘science lesson’ to help you locate these celestial bodies. The sun , moon and planets all travel in a specific path or band across the sky. This is called the ecliptical plane or ‘ecliptic’. Cuneiform writings from Mesopotamia circa 2000 B.C. have revealed to us that ancient astronomers gave names to the groupings of stars (constellations) as they watched the  sun, moon and planets pass through them each year. The Greeks adopted them from the Babylonians and passed them on to other civilizations. The word ZODIAC is a Greek word meaning a group of animals. Ancient Egypt adopted many, as well as India and China.  As time passed these constellations became known as the Zodiac and over time the number of them has varied between twelve and eighteen.

 We now have twelve signs of the zodiac. Each one covers 30 degrees of the sky for a total of 360 degrees which completes the ecliptic. Let’s name these famous constellations: Aries ( the ram), Taurus ( the bull), Gemini ( the twins), Cancer ( the crab), Leo ( the lion), Virgo (the virgin), Libra (the scales), Scorpio (the scorpion), Sagittarius (the archer), Capricornus (the sea-goat), Aquarius (the water-pourer), and Pisces (the fish). You may have noticed that I did not start with Aquarius but instead  Aries. Technically the zodiac begins where the sun falls on the first day of spring (the vernal equinox) which is in Aries.

When you go outside and see the path the sun cuts across the sky or the path of the moon, look for the constellations we named before and try to see the creatures that  ancient astronomers saw many years ago. In my next  article I will focus on a few of these constellations revealing more details about them and objects found within their fixed boundaries as well as constellations nearby. I intend to pick ones that are visible between 9 and 10 PM our time.

By Mike Hopper

Category: Other Members