Star Light, Star Bright … But Exactly How Bright?

Star Light, Star Bright … But Exactly How Bright?

NIST researcher John Woodward with the four-inch telescope used to calibrate the luminosity of nearby stars.

Credit: C. Suplee/NIST

A picture may be worth a thousand words, but for astronomers, simply recording images of stars and galaxies isn’t enough. To measure the true size and absolute brightness (luminosity) of heavenly bodies, astronomers need to accurately gauge the distance to these objects. To do so, the researchers rely on “standard candles”-- stars whose luminosities are so well known that they act like light bulbs of known wattage. One way to determine a star’s distance from Earth is to compare how bright the star appears in the sky to its luminosity.

But even standard candles need to be calibrated. For more than a decade, scientists at the National Institute of Standards and Technology (NIST) have been working to improve the methods for calibrating standard stars. They observed two nearby bright stars, Vega and Sirius, in order to calibrate their luminosity over a range of visible-light wavelengths. The researchers are now completing their analysis and plan to release the calibration data to astronomers within the next 12 months.

The calibration data could aid astronomers who use more distant standard candles--exploded stars known as type Ia supernovas--to determine the age and expansion rate of the universe. (Comparing the brightness of remote type Ia supernovas to nearby ones led to the Nobel-prize winning discovery that the expansion of the universe is not slowing down, as expected, but is actually speeding up.)

Astronomers may be able to use the NIST calibrations of Vega and Sirius to better compare the brightness of nearby and faraway type Ia supernovas, leading to more accurate measurements of the exp ..

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