Is There Another Earth? (serious)

[zaza]

visualAd always lets me down.

mendhak, however, is correct. If you pick a random few arcseconds of sky , get a big telescope and see what you can see, you'll be able to count the number and types of star and galaxy visible in that region.
Repeat a lot of times. Get an average. There's a crude estimate.

Of course, it gets more complicated than this as there is some underlying distribution...there are not the same number of galaxies in any given direction, although broadly there are a lot of similarities..

Look up the Hubble Deep Field survey and the Hubble Ultra Deep Field survey.
Given the the Deep Field survey covers, to quote the page, the area of sky obscured by a tennis ball at 100m, how can you look at that image and not be completely astounded. It's not fake, it's not a conspiracy theory. It's an actual image of what's going on out there in the big wide Universe. Amazing!
Incidentally, the count of the Deep Field image is >1500 galaxies in approximately 1 in 28 millionths of the sky. Which leads to a rough estimate of 42 billion galaxies. And that's within the visible sphere afforded by Hubble. There is plenty of Universe further away than Hubble can see.