Fritz Benedict: A more accurate yardstick for cosmic distances

A team of astronomers has devised a better yardstick for measuring distances across space. Astronomer Fritz Benedict of the University of Texas and his team have directly measured distances to five RR Lyrae variable stars. That’s important – because this type of variable star is used as a stepping stone to measure distances throughout space. He told EarthSky:

Up until our work, we’d had no really good measure of the intrinsic brightness of this kind of star. So with the Hubble Space Telescope, we’ve actually measured the distances to five of these RR Lyrae variables.

Image Credit: Ravenelle

Benedict’s team used a very precise instrument aboard the Hubble Space Telescope, combined with an old technique called stellar parallax. Parallax is really a measurement of angles – and of the change in our vantage point on a star from one side of Earth’s orbit to the other. Benedict explained:

Basically, parallax is very easy to understand. You just hold a finger up in front of your nose, and open and shut your eyes and alternate. You watch your finger bounce back and forth against a background … And the further away your finger is, the less of a bounce back there is.

Knowing the distances to RR Lyrae variable stars is important because these stars are one of the stepping stones used by astronomers to estimate distances across the universe.

The work is basically the moral equivalent of someone handing you a yardstick, and you don’t know if it’s 30 inches long or 40 inches long. Now we’ve handed you a yardstick that is either 35 inches long or 37 inches long. And that’s a much better yardstick.

By the way, one of these stars – called SU Draconis – is now the most distant star of this type whose distance has been directly measured. It’s 2,300 light-years away.

Listen to the 8-minute and 90-second EarthSky interviews with Fritz Benedict on measuring cosmic distances (at top of page.)

March 2, 2012

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