Blueshift is a direct result of the doppler effect, though they are other phenomenon that can also result in light becoming blueshifted.
As an object emitting radiation approaches an observer each subsequent photon (packet of light) is produced closer to the previous photon because of the proper motion of the object. The result is that the photon peaks appear to be closer together than they actually are, making the wavelength of light shorter (higher frequency, and therefore higher energy), as determined by the observer.
Measuring the Blueshift of Stars
By measuring the spectral shift of stars in the Milky Way, we can plot the movement of the galaxy as a whole. Objects that are moving away from us will appear redshifted, while objects approaching will be blueshifted.
Is the Universe Blueshifted?
The past, present and future state of the Universe is a hot topic in astronomy and in science in general. And one of the ways that we study these states is to observe the motion of the astronomical objects around us.
Originally, the Universe was thought to stop at the edge of our galaxy, the Milky Way. But Edwin Hubble, in the early 1900s, found that there were galaxies outside of ours (these had actually been observed previously, but astronomers thought that they were simply a kind of nebula, not entire systems of stars).
This changed our entire understanding of the Universe and, shortly after, paved the way for a new theory of the creation and evolution of the Universe: the Big Bang Theory.
The next step was to determine where we were in the process of Universal evolution, and what kind of Universe we were living in. Was the Universe expanding? Contracting? Static?
To answer these questions, the spectral shifts of galaxies near and far were measured. If the galaxies were blueshifted in general, then this would mean that the Universe was contracting and that we were heading for a "big crunch".
However, it was found that instead the galaxies were, in general, receding from us and appeared redshifted. This meant that the Universe was expanding. Not only that, but we now know that they Universal expansion is accelerating, driven my some mysterious force known, generically, as dark energy. We have little understanding of the nature of dark energy, only that it seems to be everywhere in the Universe.
