English: NGC 7331 is one of 18 galaxies chosen by the HST Extragalactic Distance Scale Key Project to calibrate secondary distance estimators. The project will use the Hubble Space Telescope to obtain an accurate distance to galaxies via Cepheid variables, with the ultimate goal of using these to measure H0 (a cosmological parameter) to an external accuracy of 10%. It was determined this galaxy is 49 million light years away (and perhaps 30,000 light years across). In this image you will see some of the nearby neighbors being both spiral and elliptical galaxies. Nearby this field (not shown) is another famous group of galaxies known as Stephan's Quintet.This image was taken as part of Advanced Observing Program (AOP) program at Kitt Peak Visitor Center during 2014.