Does it exist North of the Universe? (Which is probably used for determining coordinates of far galaxies.)
If so, then where it is?
On what is it aligned? (Is it orientated on Earth, Sun, Milky Way, Local group or on something more bigger?)


2 Answers 2


Sort of... There is a system called the International Celestial Reference System (ICRS) which has center at the Solar System Barycenter (normally inside the Sun but not the same as the Sun's center) and which has the x and y axis in the plane of the Earth's equator and the z-axis ("North" if you will) pointing towards the Celestial Pole. The x-axis points towards the equinox where the plane of the Earth's orbit and the plane of the Solar system (the ecliptic) cross (on average; this gets complicated quickly as everything related to the Earth is wobbling about on different timescales).

Note although this reference system is close to the older mean equator and equinox J2000 or FK5 system it's not actually the same as it is now defined by a set of several hundred very distant extragalactic radio sources which are called the International Celestial Reference Frame (ICRF) and which we assume don't move on the sky. The latest version of this frame is called ICRF3 and was formally adopted at the IAU General Assembly last year in Vienna. More details on how the reference systems and frames work at the USNO page on the ICRS


There are coordinate systems used on various scales, with the ecliptic system(s) useful for denoting where on Earth's sky things are, galactic coordinates for objects in and around the Milky Way, and the supergalactic coordinate system for nearby galactic clusters. This is aligned along the supergalactic plane, a plane most local galaxy clusters are aligned with. The zero point is the intersection of this plane and the galactic plane. In the SGC the north supergalactic pole is approximately RA = 18.9h, Dec = +15.7° (epoch J2000), which seems to be somewhere in Aquila. The zero point (SGB = 0°, SGL = 0°) lies at 2.82h, +59.5°, between Perseus and Cassiopeia.

The ICRS is basically the ecliptic system but centred on the solar system barycenter and oriented relative to a number of distant extragalactic radio sources unlikely to move much. So "north" in this system corresponds more or less to "north" on the usual sky sphere.

So I think one can make decent arguments that there are two possible "north poles of the universe" depending on which coordinate system one prefers.

  • $\begingroup$ In fact, there are five North poles (for horizontal (alt-az), ecliptic, equatorial, galactic and supergalactic coordinate system). But the first three poles are not universal and are changing every day, that isn't recommended for big sizes. So galactic and supergalactic systems are only correct for those North poles. +1 $\endgroup$
    – User123
    Commented Mar 7, 2019 at 13:57

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