1. The Heavens

A “star sailor” rests on our planet’s shore.  Image by Zach Dischner via Wikimedia Commons.

You and I are doing the same thing right now.  We are staring at bright screens.

We spend much of our lives in front of these screens.  They give us instant access to information and entertainment.

I teach astronomy.  When I’m out in the evening with friends or relatives, I sometimes point out objects in the sky.  But you don’t need to know anything about astronomy to do that.  You can simply hold a smart phone up to the sky.  There are apps that will show you what you’re looking at.  If you’re not satisfied with how these objects appear to the naked eye, you can quickly bring up images of them taken with the world’s largest telescopes.

We know way more about the night sky than our ancestors did.  

But we hardly ever see it as they did.  

We have other things to do at night.  Artificial lights have enabled us to work, play, and entertain ourselves after dark.  Light bulbs transformed my grandfather’s life the way lit screens have transformed mine.

But the city lights which have made our lives productive and exciting have also robbed us of the night sky which dazzled our ancestors.

Have you ever seen the Milky Way?  If so, I bet you remember where you were when you first saw it.  And how you felt.  Imagine having that sense of wonder, not once or twice in your life, but all the time.  Our ancestors did.

The Sun invoked awe.  The Moon inspired art.

The sky comforted and haunted.  Some things stayed the same from day to day and night to night.  Some things changed.  There was order and disorder.

Every day, the Sun rose in one side of the sky and set in the other side.  But it did not rise and set at exactly the same spot every day.  Or at the same time.  The same was true of the Moon, except that the changes were more dramatic from one day to the next.  

The shape of the Moon, or rather the bright part of the Moon, changed noticeably every couple of days, going from thin crescent to full and back to crescent.  

Some stars were up all night, every night.  Others rose and set like the Sun and Moon.  During the course of a night, the stars appeared to spin around an imaginary pole in the sky.  

Star trails captured on a very long exposure photograph.  You can clearly see which stars rise and set and which ones remain in the sky.  Image by LCGS Russ via Wikimedia Commons.

There was order among the stars.  They never seemed to move closer together or further apart.  You could connect them to make patterns called constellations.  A bear here.  A dog there.  A hero fighting a villain over there.

The Sun and Moon were less orderly.  They drifted from constellation to constellation.  To ancient peoples, they were divine beings along with the Earth, fire, rain, and wind.

When the Sun or Moon was eclipsed, it was seen as the work of demons.

Astronomy was integral to religion.  In many societies, the astronomer was also the priest.

Those who traveled far from home saw that the sky looked different from place to place.  By observing the sky closely, you could figure out something about where you were on Earth.

Astronomy could help you navigate.

If you were an ancient mariner on a long voyage towards the equator from the north, you would see the pole in the sky drift slowly towards the horizon.  If you went south of the equator, the stars would move clockwise instead of counterclockwise.  The Moon would still go through the same phases but the opposite side would be lit up at the same time.  The crescent that appears after a new moon would be on the left side instead of on the right.

As societies developed agriculture, keeping track of the seasons became important.  People noticed that the same constellations were visible during the same seasons.  The heavens could help you plan your plantings and harvests.

People began associating what happened in the sky with what happened in their lives.  A major celestial event, like an eclipse or the appearance of a comet, might foretell a major event in the family or society.  Thus astrology was born.  Belief in astrology was often the main driving force for astronomical observation.  The status of the astronomer-priest became further elevated when astrology was added to his or her job description.  After all, this person could predict the future.

Comet Hale-Bopp. By Philipp Salzgeber via Wikimedia Commons.

A few astronomers in a few societies carefully observed the motions of heavenly bodies.  Records of these observations were preserved, orally or in writing, for centuries and transmitted to other societies.  Coupled with mathematics, these observations allowed astronomers to do such extraordinary things as predicting eclipses.

But the single most significant thing astronomy taught our ancestors was how to keep track of time.  The Sun, Moon, and stars gave us clocks and calendars.

The history of astronomy is preserved in the calendars of the world.  By exploring them, you can discover what our ancestors knew and didn’t know, what they understood and misunderstood.

Let us start with our basic units of time.  You use them all the time but have you ever wondered where they came from?

How exactly is a day defined?  How about the month and the year?  Why are there seven days in a week?  I will address these questions in the next few posts.


Author: Bhasker Moorthy

I'm a Professor of Astronomy at Harper College in Palatine, IL, USA. My email address is bmoorthy [at] harpercollege.edu.

13 thoughts on “1. The Heavens”

    1. Never thought about it, but why are there 12 months in a year? Why is time divide in to 2 12 hour periods to make up a 24 hour period? To answer for the night and the day? Does it have to do with the zodiac signs? Why are their 60 seconds and 60 minutes in each minute and 60 minutes in each hour? 60 x 6 = 360 degrees, which perfect circle has 360 degrees the earth travels around the sun in one year. Was that the reason the unit of measurement 60 was chosen?


      1. Dividing the hour into 60 units appears to have first been done by the Mesopotamians. I’ll give a brief history of ancient Mesopotamia in a future post (it can get complicated – Sumerians, Akkadians, Assyrians, Babylonians, Neo-Babylonians) but for this, you can just look at the Wikipedia page for Base 60 (Sexagesimal). 60 is a nice number because it has so many factors including all the numbers from 1 to 6. Mesopotamians sort of had a Base 60 number system with 10 as a sub-base.

        The 24 hours thing I’ll respond to in the comments section of the next post (What is a day, really?). Next week’s post is on the month and after that, the year.


  1. Ahh… and to answer your question: the first time I saw the Milky Way was in remote northern Idaho, while on a hiking/rafting trip. I was a teenager and it indeed was an awesome sight. I grew up in the urban United States east coast and so was unprepared to see a really beautiful night sky.


    1. Matt,
      I was sleeping under the stars on Mary’s Peak about 20 miles outside of Corvallis, Oregon. I was a group of friends and we went to watch the Perseid Meteor Shower in and around the 2nd week of August… the showers were to peak at that time. The unexpected benefit was seeing the “back bone” of the milky way that night far away from the city lights and sleeping high on the tallest peak of the coastal range of mountains in western Oregon. Most awesome night I ever had!


  2. Thanks everyone. And Matt, yeah, whenever I’ve seen it, it’s also been far from civilization. I was surprised to hear one of the audience members say he used to see it all the time from Carpentersville.


  3. Very interesting writing. Time is very important and an integral part of our lives. And, no I have never seen the milky way. Not surprisingly because i was born and raised in Chicago. Too brute.


  4. This was a very interesting post. I have never seen the Milky Way, but I remember my mom always taking us outside at night when a specific comet or super moon was happening so my sister and I could see. I also remember going out in my backyard on clear nights and being able to see the stars in the sky when I was younger. We do know a lot more than our ancestors, but at the same time, we do not know just as much and there is so much more in our universe to explore and discover.


  5. This post was really interesting. All the memories of the places I visited came back to me. Remembering how the sky looked different all over the world and how magical it is. Wishing for everyone to see it and experience what I experienced.


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