prompter: Is the Sun a big star or a small start compared to other stars in the galaxy?

assistant: Our Sun is an average sized star: there are smaller stars and larger stars, even up to 100 times larger. Many other solar systems have multiple suns, while ours just has one. Our Sun is 864,000 miles in diameter and 10,000 degrees Fahrenheit on the surface.

prompter: What's the biggest star in the known universe? The smallest?

assistant: Unfortunately the questions that you are asking do not have definitive answers. Because the vast majority of stars are very far away from Earth it is very difficult to precisely and accurately measure their properties. This is a very complex problem but I will try to put it in simple terms. Essentially, while we do know that larger stars emit more light than smaller stars our measurements only tell us the fraction of that light which reaches Earth - but this alone does not tell us how bright the star actually is because it will appear more or less bright in the sky depending on how far away away it is from Earth. Therefore, for an estimate of how bright a star is in absolute terms we also need to know how far away it is. And because this is difficult to measure we do not know for certain which star is the brightest. Nevertheless, the star Stephenson 2-18 with a radius that is approximately 2150 times larger than that of the Sun is currently our best guess regarding which of the known stars in the universe is the biggest.

As for the smallest star in the known universe, that question is even more difficult to answer. The first problem is that small stars are very dim which makes it much more difficult to detect them and to measure their properties. The second problem is that small stars are much more common than large stars so the number of possible candidates is immense and the likelihood of any of them being the correct answer is diminutively small. Even tiny uncertainties in our measurements make it impossible to answer this question with confidence so we unfortunately do not know the answer and most likely never will.

assistant: The Sun is a G-class star. In the Milky Way galaxy a rough frequency distribution of the various stellar classes of main sequence stars is as follows (in order from least to most massive):

- M 76%
- K 12%
- G 8%
- F 3%
- A 0,8%
- B 0,2%
- O 0,00003%

The more massive a star is the brighter it shines and the faster it consumes its supplies of usable nuclides. More massive stars therefore have a shorter lifespan and constitute a smaller proportion of stars at any one time. Bear in mind that there are an estimated 10^11 stars in the milky way, so even the least prevalent O-class stars number approximately in the order of 10^4 stars.

prompter: Yes

assistant: Is there anything else you'd like to know about stars or the Milky Way galaxy?

assistant: Is there anything else I can help you with today?

prompter: So stars have a finite life span?

assistant: I am not sure what your question is.

assistant: The average star is about half the size of the sun, making the sun a big star when compared to other stars in the galaxy.  https://academic.oup.com/mnras/article/322/2/231/962260 describes the distribution of star sizes throughout the universe.

prompter: What is the size of a small star in comparison to the planet Earth?

assistant: The size of a small star in comparison to the Earth can vary greatly depending on the specific star in question. In general, however, stars are much larger than planets. The size of a small star, such as a red dwarf, can range from about 0.08 to 0.6 times the mass of the Sun, which is about 0.6 to 1.4 times the size of Jupiter. By comparison, the Earth is much smaller, with a diameter of about 12,742 km.

So, to summarize, a small star can be hundreds of times larger in size compared to the Earth.

assistant: It’s possible that all stars are larger than Earth. The smallest known star is 0.12 solar radii across, or about 167,000 km. That's 20% larger than Jupiter or 13 times the size of Earth.