Amanda is a retired educator with many years of experience teaching children of all ages and abilities in a wide range of contexts.
1. The Celestial Sphere
In ancient and medieval times people imagined the earth to be the center of the universe, surrounded by a “celestial sphere”. They thought the celestial sphere to be like a huge hollow ball enclosing the earth with the stars fixed to its inner surface. As the sphere rotated, so the stars moved across the sky.
While we now know the universe spreads out in all directions around us and the stars are scattered across vast distances, astronomers still use the concept of the celestial sphere to help them map the night skies.
Modern astronomy divides the conceptual celestial sphere into two hemispheres, the northern and the southern, and helps us plot the positions of stars and track their movements.
2. Visible Stars of the Northern Hemisphere
If you stand at the North Pole and gaze up at the night sky, you will see a dazzling star right in the middle. Astronomers know this as Polaris, or the Pole Star. Polaris lies above the central point of the Earth’s axis of rotation. All the other stars visible in the night sky of the northern hemisphere appear to revolve around it.
3. Visible Stars of the Southern Hemisphere
Unlike the northern hemisphere, the southern hemisphere has no star lying directly above the polar axis of rotation. So, in the southern hemisphere there is no equivalent of the Pole Star. But the visible stars in the south are far more numerous, densely packed, often brighter, and more spectacular to behold.
The image below shows the stars in the night sky of the southern hemisphere. The band of tightly clustered stars arcing across it, also visible in the northern hemisphere, is the Milky Way. The Milky Way is our “home galaxy”. It is a large, flattish, spiral galaxy that appears as a band of stars from Earth because the solar system lies in its plane.
4. The Oldest Map of the Stars
When archaeologists opened a sealed tomb in the ancient university of Jiaotong in Xian, China, in 1987, they discovered something remarkable painted on the ceiling. It was a detailed star map dating back to 25 BC.
Exploring the Night Sky Documentary
5. Why Do the Visible Constellations Change During the Year?
Because we can only see the stars at night, we cannot observe those that lie on the opposite side of the sun as seen from Earth. But because the earth revolves around the sun over the 12 months of the year, the stars hidden or seen change month by month.
During the annual cycle astronomers can see the entire celestial sphere. This movement explains why different constellations are visible from Earth at different times of the year and the stars appear to “move across the sky”.
6. The Progression of the Stars of the Zodiac
Ancient people, gazing at the night sky, associated with various constellations, symbolic figures known as the “signs of the Zodiac”. 12 of these constellations exist. They are not all visible at the same time but we can see them over the course of a year as the sun appears in front of each one.
It’s important to note that while these star constellations exist their precise astronomical dates are not the same as their “astrological” dates or significance. While a few people still believe in astrology, which claims these star clusters have a mystical influence on the lives of individual humans according to their time and place of birth, the discoveries of modern science suggest this belief is probably mistaken.
The table below shows each zodiac sign and the astronomical dates when it aligns with the sun. The astrological dates are inaccurate by about a month.
|Zodiac Sign||Dates Aligned with Sun|
21st April - 22nd May
22nd May - 21st June
22nd June - 22nd July
23rd July - 23rd August
24th August - 22nd September
23rd September - 23rd of October
24th October - 22nd November
23rd November - 21st December
22nd December - 20th January
21st January - 18th February
19th February - 20th March
21st March - 20th April
7. The True Depth of Stars in a Constellation
We are so familiar with the inner surface of the celestial sphere it’s hard to imagine the real depth of the night sky. While the stars in a constellation appear to lie on the same plane, in reality they lie at almost unimaginable distances from each other. One reason the human mind groups together stars so disassociated in space, and often time, is because from where we see them on Earth they appear to burn with similar brightness.
8. Star, Shooting Star, or Satellite?
If you’ve ever looked up at the night sky, you may have seen stars that appear to move. Those which burn brightly, fall quickly, and then fade away are not stars at all. They are meteors or comets.
Comets are chunks of natural space debris, ice and rock, which travel at the outer limits of the solar system. Occasionally particles of dust or rock from a comet fall into the earth’s gravitational field and become meteors burning up in the earth’s atmosphere. Most people know meteors as “shooting stars”.
If you see a star which seems to move across the sky at a steady pace, it’s probably a human-made satellite orbiting the earth and reflecting the sun’s light.
9. The Auroras
Most people living in North America, Europe, and Great Britain will have heard of the “Northern Lights”. Astronomers properly know the northern lights as the “Aurora Borealis”. But you may not know a southern Aurora, known as the “Aurora Australis” or “Southern Lights”, also exists.
The auroras are one of the most beautiful celestial phenomena you can see with the naked eye, filling the skies with undulating waves of luminous colored lights. The Auroras are best observed near the north or south Poles. These phenomena are caused by powerful electromagnetic waves emanating from the sun and carrying tiny particles into the earth’s atmosphere on the solar winds.
10. The Changing Shapes of the Constellations
While during a single lifetime, or even after many generations, the constellations we know today still appear the same, their shapes change over the course of hundreds of thousands of years. As gravitational forces interact, the universe continues to expand, and Earth’s orbit slowly shifts, the stars on the “surface of the celestial sphere” will move.
And so we come to the end of our exploration of the night sky. But the adventure doesn't end here. Every day, keen astronomers, both women and men, amateur and professional, continue to study the wonders of the night sky and make new discoveries all the time. When did you last look up at the stars?
© 2018 Amanda Littlejohn
Amanda Littlejohn (author) on November 04, 2018:
Thanks for your kind comment about this article.
All the primary constellations can be seen with the naked eye, just as our earliest ancestors saw them. Planets also visible without a telescope include Mercury, Mars, Saturn, Jupiter, and Venus. The Andromeda Galaxy is the most distant object in the night sky that you can see unassisted. Of course, much depends on location, time of year, and light pollution. But all of these should be visible on a clear night.
I hope that helps! Enjoy exploring the starry heavens. :)
klauli29178 on November 04, 2018:
It was good but, it didn't have enough facts for what you can see without the telescope.
Amanda Littlejohn (author) on October 11, 2018:
Thanks for your comment. I love looking up at the night sky although I recognize that for many folks that's not possible these days without making a special effort because we have so much light pollution.
When we look up at the night sky, not only do we see a pattern of stars that our ancient ancestors would struggle to recognize, but because of the time it takes light to travel such distances, we are looking back in time to the universe as it was billions of years ago. Many of the stars we see no longer exist.
I'm glad you learned something new!
FlourishAnyway from USA on October 10, 2018:
I've never been able to figure out how people look up at the mass of stars and see patterns like the Big Dipper, Little Dipper, and other constellations. And reading this, now I know that the shapes of the constellations gradually change.