Wikipedia describes the five following celestial coordinate systems each with rectangular/spherical variants:

  • horizontal
  • equatorial
  • ecliptic
  • galactic
  • supergalactic

What are the practical preferred uses of each, in relation to the others. If you were navigating within the solar system, which system would you use, or has been used by existing craft?

For example wikipedia describes the ecliptic system as "still useful for computing the apparent motions of the [celestial bodies]", which seems pretty bloody obsolete. Even though it seems to me as the most intuitively useful system.

  • $\begingroup$ In releasing the DE ephemerides, NASA has settled on ICRF, centered at our solar system's barycenter, with the xy plane set to the Earth's equator at J2000.0. naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/frames.html may also be helpful in listing/explaining the reference frames NASA and JPL actually use. $\endgroup$
    – user21
    Commented Jan 5, 2016 at 16:04

1 Answer 1


Navigating the solar system, you'd probably track your probe using Earth-based radio telescopes in the equatorial ICRF, though you might describe the overall trajectory in terms of the ecliptic.

Navigating at sea, you might measure the Sun's position in horizontal coordinates at a time in GMT to determine your own geographic coordinates.

Practical uses in backyard astronomy:

  • horizontal: telling someone where to look relative to an object on the horizon; pointing a telescope on an altitude/azimuth mount

  • equatorial: finding or plotting an object in a star atlas; choosing atlas pages to use on a given night; pointing a telescope on an equatorial mount

  • ecliptic: importing comet or asteroid orbital elements into planetarium software; planets are easiest to observe when their longitude differs most from the Sun's

  • galactic: low latitudes have more Milky Way star clusters and nebulae; high latitudes have more external galaxies

  • supergalactic: pondering the distribution of galaxy clusters?


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