In the universe there are literally billions of stars. These stars range in size, shape and color, but they are all composed of the same materials. Stars are made of 73% hydrogen, 25% helium, 2% of other elements found in space. The size of a star is measured by the radius. The radius is the length from the middle of the star to the outside edge. The unit of measurement used for comparison is the radius of our sun which is 695,500 km or (432,450 miles).
What is the largest known star?
Measuring the size of a star can be quite difficult especially when the star is many millions of light years away from the earth. Stars are also different in appearance as some have extended atmosphere, halos and dust shells or discs. As our scientific equipment is developed further and becomes more accurate it may be easier to determine the size of stars. Currently there are two stars in the universe that are recognised as the largest stars. The two stars are called VY Canis Majoris and NML Cygni.
VY Canis Majoris is a star that is located in the constellation Canis Major and is one of the largest known stars by radius. It is classified as a red hyper giant and is 1,975,000,000 kilometres (1.227×109 mi) in radius. VY Canis Majoris is 1.2 kiloparsecs (3,900 light-years) from the Earth and if the star was placed in the center of our solar system it would extend out past the orbit of Jupiter. The true size of this star is debated due to the huge amount of gas that it puts out during wild flares, making it appear larger or smaller in different viewings. It is thought that is star is either very large, so large that it does not fit with current scientific theories, or it is smaller but still reaches the most extreme limits of the scientific theory.
NML Cygni is another star that has been recognised as the largest known star. NML Cygni is located in the Cygnus OB2. This star is measured as being 1,650 times the Sun’s radius or 7.67 a.u compared with VY Canis Majoris radius of 1,420 times the sun’s radius. NML Cygni is also a red supergiant and is estimated to be around 1.6 kpc, or 5,300 light-years from Earth. From observation this star is believed to have two discrete optically thick envelopes of dust and molecules. This makes measuring the radius difficult causing debate about its true size.