New way to measure cosmic distances.

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Researchers have found a way to measure distances to objects three times farther away in outer space than previously possible by extending a common measurement technique. They discovered that a rare type of giant star, often overlooked by astronomers, could make an excellent signpost for distances up to 300,000,000 light-years--and beyond.

Cepheid variables--giant stars that pulse in brightness--long have been used as reference points for measuring distances in the nearby universe. Classical cepheids are bright but, beyond 100,000,000 light-years from Earth, their signal gets lost among other bright stars. A rare and even brighter class of cepheid--one that pulses very slowly--potentially can be used as a beacon to measure distances three times farther than their classical counterparts.

There are several methods for calculating the distance to stars, and astronomers often have to combine methods to measure a distance indirectly. The usual analogy is a ladder, with each new method a higher rung above another. At each new rung of the cosmic distance ladder, however, the errors add up, reducing the precision of the overall...