Hubble's law 2

 

The basis of measurements 

Indeed, distances from distant galaxies and their velocities must be measured. At the beginning of the 20th century, this issue was not considered, although measuring tools were already at the disposal of scientists. About a hundred years ago, everyone was convinced that the universe was infinite and static. Besides, they did not know that many of the nebulae previously discovered were galaxies like the Milky Way (our galaxy), very distant galaxies. Back then, there was no intellectual basis for measurements, was no motivation. It is obvious that even the model we built, based on the cosmological principle, would not matter. One more thing, everyone has been busy testing general relativity and building models of the universe from it - with great commitment.  To this day, this direction of interest has dominated, despite the fact that at least fifty years ago science found itself in an impasse (and is still there today). [Cosmological constant  and dark energy is a sign of a struggle for survival. Scientists do not know that the balloon of the Riemann Universe (I think) has already burst.

But it was already possible to measure. Speed ​​measurement was not as problematic (Doppler Effect), while distance measurement was challenging. It was already clear that very bright stars such as "white giants" could be used to measure distances, taking into account their brightness variation with distance. They can be identified on the basis of their characteristic spectra. It is enough to rely on the fact that visual brightness is inversely proportional to the square of the distance. However, for comparison purposes, another method had to be found. In 1912 (Henriette Leavitt) it was discovered that Cepheid stars pulsate with a frequency that depends on their absolute brightness (pulsation cycle period: 1-50 days). Cepheids are also giant stars. They were discovered in 1784 (John Goodricke). It is enough to know the pulsation period - to determine the absolute brightness. Comparing it with the visual brightness (magnitude) makes it possible to determine the distance of a given star.

 

Continued in the next article.