In addition to the size an object in space appears,?

Question

which can be deceiving, what other characteristic do scientists use to determine astronomic distances? (Choose only one of the options below.)

brightness as compared to other objects
color of the object
the light emitted by the object
radio wave signature

Answer 1

If you're in astronomy, you should know that 2,3, and 4, are all the same answers, as they are all analysis of the emission spectrum of the object. (1 can also be considered, although it does not deal with specific frequencies)

The easiest way for astronomers to determine the distance to stars, for example, is to measure the position of the "H-alpha" line. This narrow, consistent emission will be shifted very accurately in terms of its distance according to hubble's law, which states that more distant objects move more quickly away from us than nearer ones, predictably redshifting their emission spectrum.

Answer 2

Depending on the object, it is possible to use any one on your list. For example, distances to pulsars are determined by certain characteristics in the radio wave "signature".

However, the most used method (like 90% of the time) is the "brightness as compared to other objects".

If you can tell that two stars have the same spectrum (not only the color but the distribution of energy within the colors, in the light emitted by the objects) and same size, then you can tell that the one appearing 9 times brighter is 3 times closer (brightness varies as the square of the distance).

For example, it is thought that a certain type of Supernova always occurs in the same manner, with the exploding star giving off the same amount of light. We have measured the apparent intensity of that light for a supernova at a known distance. We know the type of supernova by analysing the spectrum of the light and the shape of the light curve over time.

When we detect a similar supernova in another galaxy, we measure its apparent brighness and compare it with the brightness we observed from the one at a known distance. By using the "square distance" rule, we can determine the distance to the other galaxy.


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"Redshift" is a method that is used to estimate the distance to galaxies that are very far from us. The frequency of the photons is shifted to lower frequencies (in the direction of "red" in the visible spectrum) as a result of the expansion of space between galaxies. The further away the galaxies, the more expansion there was while their light traveled to us.

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In astronomy, "light" can include any wavelength (including X-ray and radio). Therefore, any method involves the analysis of "the light emitted by the object".

Answer 3

http://en.wikipedia.org/wiki/Redshift