What is the Largest Known Star in the Universe?

Over the last two decades the improvements in telescopic design, interformetry, Space telescopes, and other advanced viewing object instrumentation, have changed much of what was classically know to astronomy. Instead of waiting for large bursts of knowledge, as when Gallileo first discovered planets around Jupiter and Saturn, and Hubble first discovered the expansion of the Universe, astronomical advances in knowledge come much more frequently. If you had asked Galilleo what was the largest planet in the solar system, he might have guessed Jupiter. But if you had asked him how many planets were in the solar system, he might have said five or six, (There are eight, Pluto is not classified as a planet any longer.)

But instrumentation measurements have made it possible to identify the stars distance, luminosity, magnitude, size, and mass, and speed or rotation.

As we walk through the collection, keep in mind that we will be comparing the size of the star in question with our Sun.

The Sun is a star. It burns hydrogen and helium in a nuclear furnace that produces the light and heat that we recognize and depend on for our survival, for all life on earth's survival.

The Sun's diameter is 865,000 miles, while the Earth's it 7,918. In other words the Sun is 109 times bigger than the Earth. Another way of looking at this is that you could fit about 1.3 million Earth's in the Sun.

The Star Sirus is just under twice the size of the Sun. Sirius is also known as the "Dog Star", because it is in the constellation, Canis Major. It is the brightest object in the sky. It is almost twice the size of the Sun.

Luyten's Star is a red dwarf star in the constellation Canis Minor and it is about 12.36 light-years from the Sun.It is about 153,000 km.in size; it is much smaller than the Sun.

Alpha-Centauri A and B are binary stars that are about 4.37 light years from the sun. They are close in size to the Sun; although one is slightly larger and the other slightly smaller.

Spica is the brightest star in the constellation Virgo located 260 light years distant from Earth. It is a blue giant, and it is about seven times larger than the Sun.

Pollux is an orange giant star, 34 light-years from the Earth in the constellation of Gemini. It is about 8 times larger than the Sun

Up until now, the astronomical sizes have been, well shall we say, manageable? Compared to the Earth, all stars seem big. But the Sun was well in the neighborhood of size. It wasn't the little kid in the block. Well, it's not that way now. The star sizes truly become large, in a gargantuan dimension. Two blue giants.Alnitak and Rigel fit the bill here.

Alnitak is a triple star system laying at the eastern end of Orion's belt. It is about 800 light years from the Sun. It is 28 times more massive than the Sun and about 60 times larger.

Rigel is 70 times larger than the Sun.It is in the Orion Constellation. It is a binary star system.

The size of the stars hereafter are truly astounding. True they are large especially as we saw with the Blue Giants. But Now we are entering into a much different area of size. These stars simply dwarf what has come before. Many of these stars are hundreds of times larger than the Sun.

One of the interesting facts about the hypergiants is their lifetime. They have very high masses but their lifetimes are very short in astronomical timescales, meaning that they only exist for a few million years compared to the several billion years for stars like the Sun. This in turn explains why it is hard to find hypergiants; they are extremely rare and only a few are known today.

Even larger stars are discussed on page 2.