The Milky Way is the galaxy in which the Solar System is, the galaxy in which our planet is located. With the naked eye and on dark nights with clear skies, we can see a part of the galaxy with the naked eye as a dense band of stars that crosses the sky.
With the naked eye you can see around 2500 stars from anywhere on the planet. About between 4 and 5 thousand in each hemisphere. With the help of binoculars or telescopes, up to 8,000 can be seen, but it is still a much lower number than the actual number of stars in the Milky Way.
But how many stars are there exactly? It is a very difficult question to answer. Impossible at present. The truth is that we do not know. We can't count every single star in the Milky Way, but we can do estimates with different methods that give us approximate ranges.
One of the most widespread estimates among astronomers is that the Milky Way contains between 200 and 400 billion starsalthough some estimates go as high as 1 billion stars (1012).
structure of the milky way
The very structure of the Milky Way is the main reason why we can only see a very small fraction of the stars that the galaxy itself contains, even with large and sophisticated telescopes.
The Milky Way is a spiral galaxy. It is like a disc with arms that rotate around a center. In this disk the vast majority of stars in the galaxy are crowded together with large clouds of dust and gas.
The diameter total of the Milky Way is about 100 thousand light years and the mean thickness is estimated at 1000 light years. The Solar System is located in one of the galactic arms about 30 thousand light years from the center of the galaxy.
Between the center of the galaxy and us, in those 30 thousand light years, there is an enormous number of stars.
We just can't see the other end of the galaxy. The stars of the galactic disc themselves prevent us. But we can't even count all the nearby stars. Light from a nearby star can be dimmed by light from a brighter star behind it or by light from a cluster of nearby stars.
The farthest stars visible to the unaided eye are approximately 1000 light-years away, with a few exceptions of very bright stars. In the Milky Way there are many very bright stars that should be seen from Earth, but in addition to stars, in the Milky Way there are also huge clouds of dust and gas that prevent you from seeing what is behind.
The vast mass of dust and gas can be seen in the night sky when looking at the Milky Way. It is the diffuse background with dark areas and bright areas that accompanies the band of stars that crosses the sky. What we actually see in the sky would be the galactic disk from within, from our position on the spiral arm.
Estimation of the number of stars
Various methods are used to overcome visual obstacles and estimate the number of stars in the Milky Way. For example, they can be used infrared telescopes (sensitive to heat) that can "see" through gas and dust. Among them we can mention the COBE (Cosmic Background Explorer), the Spitzer Space Telescope, the Wide-field Infrared Survey Explorer or the Herschel Space Observatory.
But not even all the stars can be seen with these instruments. Astronomers are forced to estimate the number of stars from the observation of other phenomena.
Following the orbit of the visible stars of the Milky Way, it has been possible to measure the speed and period of rotation of the galaxy. From our position in the Solar System, the rotation period is about 225-250 million years.
From this data it has been possible to estimate the average amount of mass, and from the total mass it has been possible to estimate that there may be between 200 and 400 billion stars in the Milky Way.
But they are estimates with a huge margin of error. First, they are estimates obtained from estimates. And second, an average stellar mass has to be assumed. You can take the Sun as a representation, but there are stars of much lower mass and there are stars of much higher mass.
So these estimates should be taken for what they are, a number to get an idea of how many stars there could be in our galaxy.
One day our technology may be able to solve the problem, see through the dust or send space probes to take pictures of the far side of the galaxy. Until then, the estimates are what we have.