Yes, a galaxy can exhibit blueshift instead of redshift, although this is less common. Blueshift occurs when a galaxy is moving towards us, causing the wavelengths of light to shorten and shift towards the blue end of the spectrum. This phenomenon is generally observed in galaxies that are part of a local group or cluster, where gravitational interactions can override the general expansion of the universe. For example, the Andromeda galaxy, our closest galactic neighbour, is blueshifted and is on a collision course with the Milky Way. This movement towards us is due to the mutual gravitational attraction between the two galaxies. Blueshift in galaxies thus indicates a localised motion towards the observer, which contrasts with the general trend of galaxies moving away from us (and thus being redshifted) due to the universe's expansion.

Yes, the redshift calculation can be influenced by factors other than the expansion of the universe. One significant factor is the peculiar velocity of galaxies, which is their individual motion relative to the cosmic expansion. This motion can be due to gravitational interactions with nearby galaxies or clusters, causing deviations from the expected redshift based solely on universal expansion. Another factor is the local gravitational field, which can cause gravitational redshift. Additionally, the accuracy of redshift measurements can be affected by instrumental limitations, such as the precision of spectroscopic equipment used to observe the galactic light. Atmospheric interference and light pollution can also impact observations from Earth-based telescopes. Therefore, while the redshift calculation is a powerful tool in cosmology, it's crucial to consider these factors for accurate interpretation of the data.

Redshift is primarily used to measure the velocities of distant galaxies, not individual stars within our own galaxy, due to several factors. Firstly, the velocities of stars within a galaxy like the Milky Way are relatively small compared to the velocities of distant galaxies. These small velocities produce very slight redshifts, often too minor to be detected or accurately measured with current technology. Secondly, the motion of stars within a galaxy is predominantly influenced by local gravitational interactions rather than the expansion of the universe. These interactions can cause stars to move towards or away from us, but also across our line of sight, leading to different types of Doppler shifts (redshift and blueshift) that complicate the interpretation of their motion solely based on redshift. In contrast, distant galaxies primarily move away from us due to the expansion of the universe, making redshift a more straightforward and reliable measure of their velocity.

The redshift of a galaxy is intimately linked to the age of the universe through the cosmological principle, which asserts that the universe is homogeneous and isotropic on a large scale. As galaxies exhibit redshift, this indicates they are moving away from us, suggesting the universe is expanding. By measuring the extent of this redshift and applying Hubble's Law, astronomers can estimate the rate at which the universe is expanding. The inverse of this rate, known as the Hubble constant, gives an approximation of the age of the universe. The principle here is that the greater the redshift, the faster a galaxy is moving away, implying it was closer to us in the past. Therefore, by extrapolating backwards, scientists can estimate when all galaxies were in a single point, which marks the beginning of the universe. This approach, while simplified, offers a fundamental understanding of the universe's age, contributing significantly to cosmological models and theories.

Gravitational redshift is a phenomenon predicted by Einstein's theory of general relativity, contrasting with the cosmological redshift caused by the expansion of the universe. Gravitational redshift occurs when light moves away from a massive object, like a star or black hole. The gravity of these objects warps spacetime and affects the light's energy. As light climbs out of a gravitational well, it loses energy, and its wavelength lengthens, leading to a redshift. This is different from the cosmological redshift, where the light from distant galaxies is stretched due to the expansion of the universe itself. In cosmological redshift, space itself is expanding, stretching the light as it travels through the universe. Gravitational redshift is thus a local phenomenon related to the intensity of a gravitational field, whereas cosmological redshift is a global phenomenon related to the dynamics of the universe as a whole.