The Hubble constant is named for astronomer Edwin P. Hubble, who in the 1920s confirmed the universe has been expanding since it exploded into being in the big bang 13.7 billion years ago.
Astronomers discovered in the late 1990s the expansion is accelerating, so determining the expansion rate is critical for understanding the age and size of the universe, researchers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said Wednesday.
Using the Spitzer Space Telescope to make the new measurements by recording long-wavelength infrared light, astronomers have refined the value for the Hubble constant to 74.3 plus or minus 2.1 kilometers per second across each megaparsec of space.
A megaparsec is roughly 3 million light-years.
"Spitzer is yet again doing science beyond what it was designed to do," JPL project scientist Michael Werner said.
Infrared vision, which sees through dust to provide better views of stars, enabled Spitzer to improve on past measurements of the Hubble constant, the researchers said.
"Just over a decade ago, using the words 'precision' and 'cosmology' in the same sentence was not possible, and the size and age of the universe was not known to better than a factor of two," said Wendy Freedman of the Observatories of the Carnegie Institution for Science in Pasadena. "Now we are talking about accuracies of a few percent. It is quite extraordinary."