Telescopes only see the brightest stars in our galaxy, and many are hidden behind gas and dust. The speed at which the stars orbit in the Milky Way indicates the gravitational pull , that is, the mass of the galaxy.
If we divide the galactic mass by the average size of a star, we will obtain the approximate figure of how many stars there are. The Gaia satellite has mapped the location of one billion stars in our galaxy, which represents 1% of the total. So perhaps the Milky Way contains about one hundred billion stars.
