Mapping the Cosmos: Counting Galaxies and Stars

At the dawn of our understanding of the universe, scientists began by observing the fiery glows of distant galaxies with the most advanced telescopes. Thanks to this immensely powerful instrument, they not only saw the number of galaxies scattered across the vast cosmos but also estimated the number of stars illuminating each one. Marking a historic breakthrough in research, initial discoveries made as early as 1924 revealed that our world is not limited to a single galaxy; rather, it is a complex system in which each stellar “neighborhood” contains hundreds of thousands of celestial bodies.

The scientific method involves a series of detailed observations and photometric studies that allow for the quantitative assessment of galaxy clusters in the sky. A prominent technique is spectral analysis—a method based on measuring redshift, which results from the Doppler effect. This phenomenon not only enables the determination of the speed of receding objects but also indirectly helps calculate their distances, making large-scale counting of cosmic objects possible. This approach continues to help astronomers, step by step, build a detailed map of the distribution of galaxies and star systems in the universe.

The culminating insight of this research is an understanding of the immense scale of the universe, where every observation transforms into a dynamic phase of cosmic discovery. The relentless pursuit by scientists for new knowledge, supported by precise measurements and data analysis, continues to expand our horizons in cosmic exploration, unveiling even more astonishing mysteries and avenues for research.

What methods do scientists use to determine the number of galaxies in the universe and the number of stars within them?

Scientists determine the number of galaxies and the number of stars they contain based on detailed astronomical observations using powerful telescopes and the analysis of obtained spectra. For instance, Edwin Hubble’s discovery in 1924, as recorded in the data, showed that the universe consists of more than just our own galaxy—several systems were studied, and based on these observations, it was concluded that each galaxy contains hundreds of thousands of stars (source: link ).

To determine the distance to remote objects, scientists use redshift measurements, which are a direct consequence of the Doppler effect. The change in the wavelength of radiation observed from receding galaxies is proportional to their speed, which indirectly enables the calculation of distances. With these methods, not only can the recession speed of objects be estimated, but a census of the number of galaxies in the universe can also be carried out, as their spatial distribution becomes accessible for study (source: link ).

Thus, the methodology includes:
1. Observations and photometric studies that allow for the quantitative assessment of visible galaxies and their clusters.
2. Spectral analysis of redshift, which provides information on the recession of objects and their speeds. These data, in turn, help correlate distances and support large-scale counts both of the number of galaxies and the number of stars within each of them.

Supporting citation(s):
"Practically, these were confirmed by American astronomer Edwin Hubble, who discovered in 1924 that the universe consists of more than just our galaxy, having discovered and studied nine galaxies using a powerful telescope. Now we know that each such galaxy consists of hundreds of thousands of stars." (source: link )

"In an astronomy textbook, a simple method is provided for determining the recession velocity of an emitting object by the magnitude of its 'redshift.' The relative change in wavelength is directly proportional to the speed of the receding source. Thus, the speeds of all astronomical objects can be experimentally determined... The Doppler effect observed in galaxies and stars allows astronomers to assess their recession speed and, accordingly, their distance." (source: link )

These methods enable a comprehensive understanding of the scale of the universe and an estimation of both the number of galaxies and the number of stars contained within each.