How do scientists estimate the number of galaxies in the universe?
We have counted them using optical ground-based and space telescopes. However we will never know how many galaxies there are outside of the observable universe.
Using telescopes such as the Hubble space telescope we have seen the most distant of galaxies scraping the edge of the light horizon. The light horizon is the where beyond it light has not has reached us,
Scientists also use the density of the universe to estimate the amount of galaxies in our observable universe.
Right now scientists estimate that there are
I hope that helps!