Note: The biggest issue I face is trying to illustrate the actual size of these Stars on a computer monitor, So I will use as many comparisons as possible to help you understand as best I can.

One of the biggest most colossal stars that has so far been discovered in the known universe is one that goes by the curios name of VV Cephei-A.  It is a binary star located in the Cepheus constellation that is 3,000 light years away from Earth.  Meaning that it still takes light 3,000 years to reach us even though light travels very fast at 186,000 miles per second.

The speed of light is a base measurement when talking about the astronomical distances the the Universe covers.

VV Cephei-A is a large star, it dwarfs our Sun and even our solar system.

VV Cephei-A is estimated to be between 1,600 and 1,900 solar radii and is also around ½ million times brighter than the Sun.

Solar radii is approximately 432,450 miles or about 110 times the radius of the Earth, or 10 times the average radius of Jupiter.

Below is just a reminder of how big the Sun is compared to Earth and the other planets, she's no mean thing !

VV Cephei-A is so fantastically big that it is difficult on a computer monitor to place a picture of Earth or even the Sun next to it for comparison of its size, as to do so would make the picture of the Sun invisible next to VV Cephei-A as a complete sphere. 

So I present a sectional view with the Sun next to it instead.

 

And this isn't  the biggest star in the Galaxy, there's a couple more, a wee bit bigger...

VV Cephei-A is only the third biggest in the galaxy, the 2nd biggest being WOH G64 at 2000 solar radii than the Sun.

Ultimately, the biggest Star in the known Universe is the hyper-giant VY Canis Majoris or in Latin: Big Dog as it is part of the Canis Majoris constellation. 

                        

At  2100 solar radii and over ½ million times brighter than the Sun.  Its volume is incredibly vast, at about ONE BILLION times greater than the Sun although its not as dense.

              

Below is a Hubble Space Telescope image of the Star, surrounded in a dust and gas cloud that is about 1 light year across.

We don't really need to be too exacting when discussing the diameter or distance of a celestial body that is millions of miles in diameter or billions of miles or thousands of light years away...

...but its nice to try and get as close as possible ! and analogies are as good a method as any to explaining this science.

Professor Roberta M. Humphreys from the University of Minnesota, USA, pictured here, intelligently estimates the radius of VY Canis Majoris is so vast that a rocket traveling at the speed of light would take 8 hours ( +/- minutes either side ) to travel around its circumference.

Along with Light Years used as a measure of distance, astronomers also use things called Astronomical Units ( AU's ) as explained further down.

Internet research constantly gave me an AU's figure of  9 for the diameter of YV Canis Majoris, but I have proved this to be incorrect.  So based on Professor Roberta Humphreys findings I have worked out the AU figure to be closer to 19, explaining how I worked it out it in the next paragraphs...

...VY Canis Majoris then has a diameter of 19 Astronomical Units (AU's) which is the equivalent of nineteen times the distance between the Earth and the Sun.  viz: The mean distance from the Earth to the Sun is  93million 20 thousand miles x AU's 19 therefore results in YV Canis Majoris having a diameter of about (n) 1 billion 767 million 380,000 miles.  Which is (n) x π (*3.142) = 5 billion 553 million 107,960 miles which would equate with light taking 8 hours to travel its circumference @ 186,292 mi/p/s x 60 /sec x 60 /min x 8 hr = 5 billion 365 million 209 thousand 600 miles.

Leaving a small discrepancy of only 187 million 898, 360 miles or just under 17 minutes.

Another way to illustrate the size,  if it were possible to  drive on the surface of Canis Majoris, at 300 mph non stop 24/7, it would take 2113½ years to drive around the entire circumference and the speedometer's trip  would show 5 billion 553 million 107 thousand 960 miles  compared with 3½ days to do the same thing on the Earth, with its equatorial circumference of 24,901.5 miles.

* I rounded up pi to 3.142 for an easier to understand equation, unadjusted π @ 3.141592>  leaves me a deficit of  -0.00127%

 viz: 3.14200000 - 3.14159265 = 0.00040735.  Then we multiply the answer by the the first sum 0.00040735 x 3.14200000 to arrive at 0.0012798937 which is now minus as a small percentage.

Below is a comparison scale, the Sun is invisible when placed directly next to it at this scale, the white rectangle with the image of the Sun in it has to be magnified many times, so that we can see it !

Another view, the Sun is a pinpoint above the word "Our Sun " but our huge Sun is invisible at this perspective as VY Canis Majoris is just too colossal.

 

VY Canis Majoris is indeed astronomically colossal, it is known as a red hyper giant and is located in the Canis Majoris constellation.  It currently resides at about 5,000 light years away from Earth.

A typical red hyper giant phase lasts about ½ a million years. A massive star becomes a red hyper giant near the end of its life, as it burns up all the hydrogen fuel at its very core.  

As the core contracts under its own gravitational pull, the outer layers of the star will expand 100 times larger than its original size, and it rapidly begins to lose mass.  It has been assessed that VY Canis Majoris has already exhausted about half of its mass, and at a tremendous rate due to its brightness too.

It will eventually explode as a supernova estimated around the year 3200, when it does, the fragments will all become the building blocks for new stars in the ever changing, ever active, all wonderful, truly majestic and mystifying Universe.

Below VY Canis Majoris stands out...just a little bit !

Simply though, VY Canis Majoris is a dying star, shedding off huge amounts of matter into the surrounding nebula that makes it hard for Hubble to clearly see with any great definition.

VY Canis Majoris may not actually be the largest star in the Galaxy but at present its the only one we know about until a much more powerful telescope is created.

Not wanting to worry anyone, but our Sun, being a star as well, will also self destruct...but in a few million years ( it is hoped ) and it will burn up our Earth and indeed the entire solar system with it as it expands outwards before blowing up.

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