* Vastness of the universe: We can only observe a tiny fraction of the universe.
* Star formation is ongoing: New stars are constantly being born, and some main sequence stars will eventually evolve off the main sequence.
* Difficult to count: It's very hard to determine if a distant star is on the main sequence just by looking at it.
However, we can make some educated guesses:
* Dominant stage: The main sequence is the longest and most stable stage in the life of a star.
* Most stars: It's estimated that over 90% of stars in the Milky Way galaxy are currently on the main sequence.
So, while we can't know the exact number, it's safe to say that the vast majority of stars in the observable universe are main sequence stars.
