Final answer:
Type Ia supernovae are useful as distance indicators because they can be seen from very far away, and serve as accurate luminous markers for measuring vast cosmic distances.
Step-by-step explanation:
Supernovas, specifically Type Ia supernovae, are extremely useful as distance indicators because they can be seen from very far away; this makes them accurate standard bulbs in determining cosmic distances. These stellar explosions are not frequent but provide a consistent brightness that allows astronomers to measure distances to far-off galaxies. By observing the apparent brightness of these supernovae and knowing their intrinsic luminosity, astronomers can calculate the distance to the supernova and hence the host galaxy.
Unlike Cepheid variables and RR Lyrae stars, which are limited to distances within our own and nearby galaxies, Type Ia supernovae can be detected over much greater distances in the universe. However, they are not always found near RR Lyraes or Cepheid variables, which are different types of standard candles used for measuring cosmic distances.