Distances are notoriously difficult to measure in astronomy. Astronomers use many methods for estimating distances, but the farther away an object is, the more uncertain the results. Cosmological distances, distances on the largest scales of our universe, are the most difficult to estimate. To measure the distances to the farthest galaxies, those gravitationally lensed by massive foreground galaxy clusters, astronomers really have their work cut out for them.
If a massive stellar explosion, known as a supernova, happens to go off in a galaxy and we catch it, then we can use the “standard candle” method of computing the distance to the galaxy. Supernovae are expected to be discovered in the Frontier Fields, but not at the numbers that will help us find distances to most of the galaxies in the images. Without these standard candles, astronomers must use other means to estimate distances.
A Spectrum is Worth a Thousand Pictures
One of the more accurate methods for measuring the distance to a distant galaxy involves obtaining a spectrum of the galaxy. Getting a galaxy’s spectrum basically means taking the light from that galaxy and breaking it up into its component colors, much like a prism breaks up white light ...