For those of you , who understand the rudimentary of space science, the universe is expanding. To the point where one day, the overall energy in space will be sparse. Meaning, Energy is never created nor destroyed (Newtonian physics). Meaning space will freeze over someday. Why is Space Expanding. It is because of dark energy. You may have heard of dark matter comprises some 80% of all matters in our universe. No one has ever detected it. It is just observed. How do we know space is expanding, or dark energy is pushing out the galaxies from each other. We see the red shift. As opposed to the blueshift. Our neighbor Andromeda Galaxy will collide with the our own galaxy someday in the future. Hence we see the blue shift when we observe giant Andromeda. Don't be afraid, the collision will occur far far into the future. By then, our very own loving sun will torch us to death. In 500 million years, the sun will be so hot, mother Earth will practically melt.
Call that your lesson in Astronomy/Physics for the day.Doppler blueshift is used in astronomy to determine relative motion:
The Andromeda Galaxy is moving toward our own Milky Way galaxy within the Local Group; thus, when observed from Earth, its light is undergoing a blueshift.
Components of a binary star system will be blueshifted when moving towards Earth
When observing spiral galaxies, the side spinning toward us will have a slight blueshift relative to the side spinning away from us (see Tully–Fisher relation).
Blazars are known to propel relativistic jets toward us, emitting synchrotron radiation and bremsstrahlung that appears blueshifted.
Nearby stars such as Barnard's Star are moving toward us, resulting in a very small blueshift.
Doppler blueshift of distant objects with a high z can be subtracted from the much larger cosmological redshift to determine relative motion in the expanding universe.[2]