How do we estimate $10^{23}$ stars in the observable universe?

Question

Now, I read somewhere, that there are 4,106,234 stars in the observable universe. How did scientists estimate this?

Answer 1

The simple answer is statistics. We can measure the number of starts in a finite area and check that same size area in several locations to estimate how many stars are in our galaxy. Once we've done this then we can estimate the total over the whole surface area of the sky. We do something similar with "deep field images" looking at a narrow patch of sky and counting the total number of galaxies in that patch, repeat for a few other locations to check that the number of galaxies is relatively constant (or to find an average if they are not) and then extrapolate to the whole surface area of the sky.