Articles Science and Education

Airtract UV VV Astronomy humbles me.

What does the night sky teach us about the universe? (1.0) 09 May, 2020   


1.1. Introduction

1.2. Facts and exploration

1.3. Observable universe

1.4. Rest of the universe

1.5. Expanding observable universe.

1.6. Conclusions / Pavement to next topic of article.


As a child when we went to the terrace of our house during night with our parents, we children were restless. Disturbing the peaceful and romantic environment. Our parents used to come up to us and say " Hey chap! Why don't you count the stars up in the night sky? " Out of curiosity, we begin our count " one, two, three... " As we keep counting, we realize that we are running into more uncounted stars. More and more stars appear to our eyes that we hadn't counted yet. 

These times were precious, not only because of we living a stress-free and responsibility-free life, but also for the first discoveries we made. This was the first time we thought " If there are so many stars in the sky, and every star is lit, then why is it dark during night?  " 


Enough with the stories, lets get scientific. 

What we know till date is, " There are an infinite number of stars in the universe ". " Every star emits energy in the form of a photon ray which are detectable to the naked eye and travel at the speed of light. " Finally, " You will bump into a star, no matter which way you travel in the universe in a straight line. "

Putting these in perspective, our night sky is supposed to look white and bright with stars all around. So, why does our night sky seem dark ? Is it that what we have learnt till date is wrong? Or is there an extension to this theory? Or is it the curtains to prove what we call an " infinite universe "?

The average rate of expansion of the universe is 72 Kmps. And, the universe is about 93 billion light years across in diameter. There are 1 billion trillion stars in the observable universe. 1 billion trillion stars does not seem like it can make the night sky too bright, considering the fact that at least half of the number of stars will be " behind the sun ".


What we are forgetting is, all these facts only apply to the "Observable universe ". 

Click on the images and zoom in to see clearly.

While the observable universe can be defined in a monotonous way, " The observable universe is a spherical region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. " Let us make it understandable and easy to comprehend. 

The observable universe is everything we can see. The last ray of photon from the farthest star is our horizon. We can only predict what is beyond it. Interestingly, our observable universe also expands. How does this happen? Our horizon does not expand, we cannot see what is beyond the horizon, then how can the observable universe expand?


Before we answer why and how  the observable universe expands, we must first answer the question, why does the observable universe even exist? Or in simple terms, " Why can't we see the entire universe? "

The answer to this is rather simple. It is just because the speed of light is not fast enough. What does this mean? Consider a hypothetical situation, the universe is stationary. It is of 93 billion light years in diameter. Now, you set out on a journey at the speed of light from one end of the universe, to the other. With the current situation, it would take you 93 billion years to reach the other end. 

So what does this have to do with our question. Well, lets just put that number into perspective. The universe itself is just 13.6 billion years old. So if we actually had such a journey and started it with the big bang, then we are just about 1/10th of the journey in.

That means, a star that is 30 billion light years away from earth, will not be seen from earth already, simply because the first rays of photons that left the star did not reach us yet. This leads to a remarkable line of difference between the stuff we can see and what we cannot see, or rather scientifically, the observable universe .


Now, we can answer " How the observable universe expands ".

Consider a star, just outside our observable universe. So, we cannot see it yet. The reason being, its first photon has not reached earth YET, but the fact is , the photon is on its way. A few years later, considering the relative speed of the photon with respect to the expanding universe, the photon will have reached earth.

This means we are now seeing a step further from our previously considered 'observable universe'. What could be the only logical explanation, the observable universe has expanded. This process continues, until the universe itself collapses.


This could lead us to numerous conclusions. Such as:-

1) Our universe is the only one and extends to infinity.

2) Our universe is expands faster than the observable universe.

3) Our universe does not even expand, if we are the center of our observable universe, and if it is already infinity.

Although every theory can be classified as correct, all we can do is sit up in the terrace tonight and come up with another question, " What if the multiverse theory is true?  "

Will there be other life forms? Will there be more than one you? If yes, what will they be doing? The physics and math of the other universe? And most importantly, what is between any 2 universe?

astronomy space physics science night sky stars universe observable universe logic photons light outter space multiverse infinite universe expanding universe paradox theories

Related Articles

What does the night sky teach us about the universe? (3.0) What does the night sky teach us about the universe? (2.0) Mars Colonization: A myth or a Destiny.

Comments 1


UV VV - My "What does the night sky teach us about the universe? (2.0)" is out.... be sure to continue reading. And thanks for t... Read More

UV VV - My "What does the night sky teach us about the universe? (2.0)" is out.... be sure to continue reading. And thanks for the support. Read Less


Science and Education Courses

Philosophy of Logic

S M Nazmuz Sakib

0 (0) New Course

This course will help you think more clearly through many of life's dilemmas and difficult situations. Some logical fallacies you might be familiar with are: Ad hominem, begging the question, red...

10 hrs 4.27 mins 7 Students Enrolled 22 Lectures

$ 0.00

Free Enroll Now

Philosophy of Astrobiology: An introduction

S M Nazmuz Sakib

5.00 (2)

Astrobiology, formerly known as exobiology, is an interdisciplinary scientific field concerned with the origins, early evolution, distribution, and future of life in the universe. Astrobiology cons...

6 hrs 44.6 mins 29 Students Enrolled 12 Lectures

$ 0.00

Free Enroll Now

Digital Logic Design


5.00 (13)

To introduce the theoretical and aspects of digital electronics, which is the back bone for the basics of the hardware aspect of computers and other modern electronic gadgets

33.52 mins 115 Students Enrolled 4 Lectures

$ 0.00

Free Enroll Now

Upgrade your Vocabulary- 100 Advanced Words for En...


0 (0) New Course

Fuel your vocabulary today by taking this advanced course rapidly

51.39 mins 0 Students Enrolled 3 Lectures


67.80 % off $59


Buy Now
View All
Item added successfully. Go to cart for checkout.
Accept Reject