Measuring Extinction Towards An Object
To measure the extinction curve for a star, the star's spectrum is compared to the observed spectrum of a similar star known not to be affected by extinction (unreddened). It is also possible to use a theoretical spectrum instead of the observed spectrum for the comparison, but this is less common. In the case of emission nebulae, it is common to look at the ratio of two emission lines which should not be affected by the temperature and density in the nebula. For example, the ratio of hydrogen alpha to hydrogen beta emission is always around 2.85 under a wide range of conditions prevailing in nebulae. A ratio other than 2.85 must therefore be due to extinction, and the amount of extinction can thus be calculated.
Read more about this topic: Extinction (astronomy)
Famous quotes containing the words measuring, extinction and/or object:
“Man always made, and still makes, grotesque blunders in selecting and measuring forces, taken at random from the heap, but he never made a mistake in the value he set on the whole, which he symbolized as unity and worshipped as God. To this day, his attitude towards it has never changed, though science can no longer give to force a name.”
—Henry Brooks Adams (1838–1918)
“I wish all men to be free. I wish the material prosperity of the already free which I feel sure the extinction of slavery would bring.”
—Abraham Lincoln (1809–1865)
“...if we would be and do all that as a rational being we should desire, we must resolve to govern ourselves; we must seek diversity of interests; dread to be without an object and without mental occupation; and try to balance work for the body and work for the mind.”
—Ellen Henrietta Swallow Richards (1842–1911)