How Big Are the Stars?

Look up into the sky during the day and you will see the glowing disk that is our Sun the closest star to Earth. Look up into that same sky at night and you will see countless twinkling points of light, the size of a grain of sand. Yet some of those twinkling stars are hundreds of times larger than our own star. Just how big are the stars?

From Dwarfs to Supergiants

Like most things in astronomy, we measure stars based on a reference point that makes sense to us—the Sun. In terms of mass we say “This star is 5 solar masses” and that means five times the mass of our sun. Likewise, when discussing the diameter or radius it is multiples of the sun. Stars are big, no question about it, but in comparison to each other, some may seem very small while others are very, very large indeed.

The smallest stars are red dwarfs, which are about 0.1 the radius of the sun, or 70,000 kilometres. Compare that to Earth, which is roughly 14,000 kilometres in diameter, and the red dwarf is very large after all. The sun, about 100 times the size of the earth, is actually quite an average size for a star. When scaling the chart of star size up into the giant and supergiant sizes, stars 100, 300 and 600 times the size of the sun start popping up. Belteguese, the largest named star discovered so far, is approximately 650 times the size of our sun.

Star Mass

Besides the amount of space a star takes up, stars are also measured by their mass. If you took the mass of Earth and put it on one side of a galactic scale and put the mass of the sun on the other, the sun would certainly keep its side down. You would have to pile up over 300,000 Earths to come close, and around 340,000 to make the scale tip in the other direction.

Jupiter is one of the most massive planets in our solar system, weighing in at a little over 300 Earths, yet even the least massive star that has been discovered to date is about 93 times more massive than Jupiter. The most massive stars found are estimated to be between 100 and 150 times more massive than our sun (45 million Earths), which is believed to be the biggest a star can get in this period of the universe’ life span. Due to the dearth of heavier elements at the beginning of the universe, the theory is that some stars were able to achieve a mass of 300 times that of the sun (90 million earths).

Mass and Lifespan

The more massive a star, the shorter its lifespan is thought to be. The most massive stars are thought to last only a million years, thanks to the incredible pressure placed on the core, which causes it to burn hydrogen more rapidly. Most observed stars are thought to be somewhere between one and ten billion years old. Our own star is thought to be middle aged at around 5 billion. Some very small stars are thought to have a life span in the hundreds of billions of years.

Final Thoughts

How big are the stars? So big it very nearly defies comprehension. It is interesting to note that as we use our star as a measuring stick and then examine other stars in comparison to ours that the Sun turns out to be fairly average—a very convenient thing for a measuring tool.

Related Articles in the 'The Stars' Category...

• How Far Away are the Stars?
• Main Sequence Life of Stars
• Pioneer Plaques
• Star Formation
• The Death of Stars
• The Milky Way
• Types of Star
• Using Constellations to Find Other Constellations
• What Are Star Remnants?
• What's Inside a Star