# How is the distance measured in light years

03/30/2002 / Author: Franz SchmiedAstronomy> observation

Distance measurements in space

How do you measure the distance to distant stars?

 Trigonometric parallax measurement.(Image: Prof. Edward L. Wright, University of California)
Two methods are used to measure distances in space, direct and indirect measurement. Direct measurement was only possible through the construction of particularly powerful telescopes. This measurement is also called Trigonometric parallax measurement designated.

How does this measurement work now? The angle to the star in question is measured on any given day. Half a year later, the angle is measured again. You can see a difference and use trigonometry to calculate the distance. In the past, both of these were used to achieve the highest possible accuracy Equinoxes (Equinox).

Thales had already used the triangulation method in the sixth century BC to determine the distance of a ship from the coast. The angles are measured from two different points of view A and B at a distance AB a and b. With these two angles you can construct a triangle and thus determine the distance. In our case, the distance between the two points A and B corresponds to twice the distance between the sun and the earth, as there is half a year between the two measuring points.
However, the direct method can only be used for stars in the immediate vicinity. It is sufficient for distances of about 150 light years.

The indirect method is based on color and intensity measurements. The color measurement is based on the Doppler effect. The Doppler effect says that light emitted by objects moving away from the earth shifts into red. This redshift is proportional to the distance between the object and the earth.

The intensity measurement assumes that certain stars and nebulae have the same luminosity everywhere in the universe. If we now receive an attenuated light beam, the distance can be determined on the basis of the attenuation.
With the help of indirect measurement, we are able to determine distances of over five billion light years.