Standard Candles

Standard Candles

Bright beacons that serve as reference points. One kind of standard candle are the Cepheid variables (the North Star is one), so called because they blink at a rate that is precisely related to their brightness. Because the brightness of individual stars is proportional to their distance from us, cosmologists compare nearby Cepheids (to which we know the precise distance) to those farther away. A Cepheid that is four times fainter than a nearby Cepheid is estimated to be twice as far away. Cosmologists use an entire ladder of distance indicators that are calibrated using the lower (nearest) rungs.

Source: "Measuring the Shape of the Universe with Supernovae"

http://www.ngst.nasa.gov/science/firstSN.html Last modified 26-May-2000 [Date accessed 6 June 2000]

The two objects represented by the red and purple dots with rays emanating from them are at differing distances from the telescope tube. The objects are presumed to be of equal intrinsic brightness (denoted by the same number of rays from each). Notice how the object closer to the detector has more of its light intercepted by the detector and hence is received to be brighter. By comparing the difference in brightness we can measure the relative distances of the two 'beacons'.


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Date Created 1 June 2000
Last Updated 11 June 2000