When we look into the beautiful sky in the night, exclaiming how beautiful these shining stars are. My question is how could we tell, whether any of these shining "point" is a star or a galaxy?
If indeed many of these are shining galaxies, then what roughly the percentage is of these shining galaxies in the sky (using the naked eye only without telescope)? (And why.)
Best Answer
With the naked eye, virtually every point you see is a star.* That's because there are very few galaxies that are visible with the naked eye.
With telescopes, for many galaxies you'll be able to resolve multiple light sources (aka. stars). That lets you tell it's a galaxy. For those galaxies that are further away, you can still tell by taking a spectrum. Galaxies have fundamentally different spectra from stars, because they're composed of lots of different stars at different metallicities, temperature, etc (+ other stuff).
The percentage of stars/galaxies you see depends on what you're using to observe. In the Hubble Deep Field for example, virtually every point is a galaxy. Comparatively, if you're using an ordinary pair of binoculars, virtually every point is a star.
*Some of the brightest points will not be stars, but planets.