Supernovae of type Ia can be used as standard candles to determine extra-galactic distances. But these event only occur (roughly) once every 200 years in any given galaxy and rapidly fade away. So to actually see a supernova in another galaxy, you have to be observing a lot of galaxies for a long time. This makes it seem like this isn't a very practical method to determine extra-galactic distances. To how many galaxies has the distance been determined using type Ia supernovae?

  • $\begingroup$ "standard candle" is the keyword :-) Note, in the last 50 years, we could have seen supernova in 25% of the galaxies. $\endgroup$
    – peterh
    Jan 22 '20 at 14:52
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    $\begingroup$ ...of the galaxies that we have been looking at non stop. $\endgroup$
    – usernumber
    Jan 22 '20 at 14:53
  • $\begingroup$ Enough if we make a single photo about it in the $\approx$ 1 month until the SN is visible. $\endgroup$
    – peterh
    Jan 22 '20 at 14:55
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    $\begingroup$ This paper mentions using 740 spectroscopically confirmed type Ia supernovae with high quality light curves arxiv.org/abs/1401.4064 $\endgroup$
    – D. Halsey
    Jan 23 '20 at 0:46
  • $\begingroup$ No, it isn't a good way of determing distances if your aim is to determine the distance to every galaxy. But thast isn't what they are used for. $\endgroup$
    – ProfRob
    Jan 29 '20 at 11:06

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