# Determining Distances in Space [closed]

I suspect the scope of this question may be to broad, but: what are some methods for determining distances between two objects in Space? Please present the methods in historical order, so as to make the evolution from primitive methods to modern ones clear.

• Welcome to Astronomy! If you're looking for history, you could try us at HSM. Otherwise, see this and this. Nov 23, 2014 at 19:17
• The second link by HDE 226868 links to thisCosmic Distance Ladder which fits your main question. But it doesn't give historical sequence. It does indicate that historically Venus was important for determining the AU. Nov 26, 2014 at 21:02

There are a few methods that could be used to measure distances to objects in space. I'm not sure of the ages of these methods, but in many cases, the smaller-scaled methods tend to be older (as we simply didn't know about the larger scale).

The scale of the solar system was initially calculated using the parallax effect - measuring the position of Venus relative to the Sun at different times from several places across the Earth, during a transit. We can use orbital velocities nowadays to calculate average distances from the Sun. In some cases, we can use the light travel time to orbiting satellites to calculate distances very accurately, too.

For nearby stars, the main method is to measure the change in position of the star as the Earth moves across its orbit. This also uses the parallax effect.

For more distant stars, scientists often need to use specific variable stars (such as Cepheids, and RR Lyrae type stars), whose variations are related to their mass. Scientists can then use this data to calculate distance.

Cepheid variables are also used for measuring distances to nearby galaxies.

For more distant galaxies, scientists can use redshift to calculate distance, as more distant galaxies are receding faster than nearer ones, causing a larger doppler effect.

Another method for measuring extremely distant objects is to look for Type 1a supernovae, which, since they always have the same luminosity (their mass is always the Chandrasekhar limit, or about 1.4 solar masses). This was used to calculate that the expansion of the universe was accelerating. However, this method isn't used very often, as these supernovae don't happen very often.

• Are you sure parallax was used to calculate the distance to Venus? It would move so much that it would actually change position between the measurements, throwing everything off. Nov 23, 2014 at 19:38
• Honestly, I was being nit-picky. I upvoted because this is just as comprehensive an answer as the question seemed to be looking for. Nov 24, 2014 at 2:07