Scientists use an instrument called spectroscopy that separates light into wavelengths of color. Higher-energy, shorter-wavelengths, violate-colored light, to lower- energy, longer-wavelengths, red-colored light. If a star is moving towards you, the wavelengths will be more compressed and more shifted towards violate on the color scale. If a star is moving away from you, there will be a red shift which means the wavelengths will get longer and it will be stretched out and shifted towards the red on the end of the spectrum. Astronomers have observed the red shift on multiple individual stars as well as collections of stars. Astronomers infer that stars and galaxies are moving away from and away from each other. Which in conclusion means the universe is expanding.
Technology helps our understanding of the universe Astronomers use instruments Like the Hubble telescope to gather information around 120 gigabytes of information every week the Hubble sent back to earth. 100 years ago we didn‘t have the same knowledge as we do now because all this technology we have has changed theories and we've learnt more. We have the ability to explain observations and theories that have happened already. Technology has helped us to be able to discover and see lots of celestial bodies or in other terms objects such as the moon, the sun etc.
Most galaxies started in the same area in space, but since all galaxies were moving away from earth and each other that is how they got to were they are in the present time. Edwin Hubble figured out that the galaxies weren‘t just moving away but they were moving at speed that was proportional to their distance. As the universe continues to expand the distance between all the galaxies gets larger.