I may hold the distinction of being the only astronomer to have been trapped in a cage at the top of a large telescope on the 14,000-foot summit of Mauna Kea. (I know another astronomer who once fell out of such a cage, but that is another story.)
Figure 1. Spiral galaxy NGC 4414 is speeding away from us as it is carried by the expansion of the universe. The rate at which the universe is expanding, described by the Hubble constant, is determined simply by measuring the velocities and distances of galaxies. In practice, however, making accurate measurements to distant galaxies can be extremely difficult. The launch of the Hubble Space Telescope in 1990 made such measurements much easier, allowing astronomers to determine the distances to galaxies with an unprecedented level of accuracy. After nearly a decade of measurements, astronomers have derived a value for the Hubble constant that is accurate enough to be used meaningfully in various cosmological and astrophysical calculations. NGC 4414 is nearly 19.1 megaparsecs away (roughly 62 million light-years), and it is receding from us with a speed of about 1,400 kilometers per second.
Image courtesy of NASA, Hubble Heritage Team, STSci/AURA and Wendy Freedman.
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