Welcome to brain Stuff from how stuff works dot com where smart Happens. Hi, I'm Marshall Brain With today's question, how are astronomers able to measure how far away a star is? It turns out that measuring the distance to a star is an interesting problem. Astronomers have come up with two different techniques to estimate how far away any given star might be. The first technique uses triangulation or parallax.
The Earth's orbit around the Sun has a diameter of about a hundred eighty six million miles or three hundred million kilometers. By looking at a star one day and then looking at it again six months later, and astronomer can see a difference in the viewing angle for the star. With a little trigg, the different angles yield a distance. This technique works for stars that are about four hundred
light is away from Earth or closer. There's no direct method currently available to measure the distance two stars further than four light years from Earth, so astronomers instead use brightness measurements. It turns out that a star's color spectrum is a good indication of its actual brightness. The relationship between color and brightness has been proven using the several thousand stars that are close enough to Earth to have
their distance measured directly. Astronomers can therefore look at a distant star and determine its color spectrum. From the color, they can determine the star's actual brightness, and then, by knowing the actual brightness and comparing it to the apparent brightness seen from Earth, that is, by looking at how dim the star has become once it's light reaches Earth, they can determine the distance to the star. For more
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