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24 Calibrators 16 Fornax (/i= 31.24) 38 Ursa Major (/i= 31.34) 53 Pisces (îî= 33.89) 28 Coma (/i= 34.67) 20 Abell 1367 (fi= 34.70) 179 Total

24 Calibrators 16 Fornax (/i= 31.24) 38 Ursa Major (/i= 31.34) 53 Pisces (îî= 33.89) 28 Coma (/i= 34.67) 20 Abell 1367 (fi= 34.70) 179 Total

calibration is complicated by the fact that the relationship may depend on the type of galaxy.

Even with these methods, there is another nagging problem. When we look at a distant galaxy, we are seeing it as it was a long time ago. However, we know that galaxies evolve. As they evolve, their luminosity changes. Luminosity calibrations on nearby galaxies might not apply to distant galaxies.

More recently supernovae have been an important tool. We can see supernovae far away, especially with HST. One is shown in Fig. 18.15(a). From

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