# Triangulation for astronomical distances

How can triangulation be used to calculate the approximate distance to very distant celestial bodies like stars, globular clusters, etc.? And can it be used to measure the distance to a black hole?

• Have a look at en.wikipedia.org/wiki/Parallax. The parallax method only works for nearby stars. The nearest black hole is too far away for parallax to be any use. Likewise globular clusters. Jun 7, 2012 at 16:40
• @JohnRennie The nearest known black holes are one or two kiloparsecs away.
– user137289
Feb 20, 2018 at 13:41

## 1 Answer

Measure the angular distance between a star and the distant background stars.
Repeat 6months later when the Earth is on the opposite side of the sum

If you know the length of the baseline (the Earth's orbit) and the angle then you know the distance to the star. In fact we define the distance to stars in terms of this angle and the Earth's orbit - see http://en.wikipedia.org/wiki/Parsec

Because of the blurring effects of the atmosphere it's difficult to measure angles much less than 1 arcsec, and so determine the distance to stars more than a few parsecs away directly by this method.

The hipparcos satelite was able to make much more accurate measurements ( less than 1 milli-arcsec) and so measured distances 1000x further

• It is my understanding that the Gaia spacecraft is currently on an extended measurement campaign that improves the hipparcos resolution down to a few μas, at least for some stars, with an initial data release in September 2016 and a second instalment coming in April 2018; maybe it's worth including a mention in this answer. Feb 20, 2018 at 13:28
• And there is also radioastronomy.
– user137289
Feb 20, 2018 at 13:46