Final answer:
A poor distance indicator to galaxies is the measurement of parallax, since galaxies are too distant for this method to discern any shifts. Other methods like variable stars and Hubble's law are used instead, with new techniques improving accuracy.
Step-by-step explanation:
A method that is not a good distance indicator to galaxies is the measurement of parallax, which is effective for stars within our own galaxy but not for distant galaxies. Parallax involves measuring the apparent shift of an object's position against a distant background as the Earth orbits the Sun. This method works for stars within the Milky Way because they are relatively close, allowing for measurable parallax shifts. However, galaxies are much further away, and any parallax shift that might occur is too small to detect with current technology, making it an unreliable distance measure for galaxies.
Instead, other methods like observing variable stars such as Cepheids, which have known brightnesses and can be used to measure distances further out, are used. Additionally, for very distant galaxies, astronomers rely on Hubble's law, which correlates the redshift of a galaxy with its distance from us. Nevertheless, these methods have limitations, and accuracy decreases significantly as the distance increases. Interstellar dust and gas can also dim the light and lead to an overestimate of distances, which is why new techniques in the past few decades are important for providing more reliable measures within an accuracy of about 10%.