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Coordinate space
Hi, I'm a GIS mapper w maps of Moon & Mars in those co-ordinate spaces. Here, what's the coordinate space that objects such as the Milky Way are mapped in to keep track of their position and their movement. Where is what's the origin of such a coordinate space--is it the Earth's position in the cosmos or some other location? (2/17/2025 Joe Kerski "Spatial Reserves" open data blog)
Answer
Dear user, thanks for your inquiry.
In astronomy many coordinates systems exists to map the location of celestial objects, that serves different purposes, i.e. to easily manage the data in a more natural framework.
The argument is very vast and cannot be shortly explained in a web ticket, we will provide a brief introduction and some supporting links that could help to understand the big picture.
Like in Earth cartography the definition of a common and uniform coordinate system it has also a long history and there is a strong connection between Earth coordinates and celestial coordinates, and this fact was used by sailors for many centuries for determine their point on open sea, determining the altitude and azimuth of some known stars and Sun and hence determine their position.
But how the coordinates of these stars were and are defined? in ancient times the reference system was based on the ecliptic (the theoretical big circle in the sky) that "contains" the movement of the Sun and the planets, counting the celestial longitude on this circle, and the latitudes as distances from it.
However more recently it was introduced a system, the equatorial system that connect Earth and time to the position of stars in the sky. This system is what is actually used in astronomy. The system is defined in this way:
The big circle corresponding to the projection of the Earth equator on the sky (called the celestial equator), is the reference for the "longitude" that is called in astronomy Rigth Ascension (RA), the perpendicular angular distances to this circle measures the "latitude" that is called Declination (DEC). The zero point of the Rigth Ascension, is measured from the point of the Sun at the equinox of March (i.e. at the intersection of the ecliptic with the celestial equator).
As you can understand, non uniformity on Earth figure, precessional motion, polar motions, all alter this definition.
For creating a fixed reference in space that was not subject to all these problematics, it was created a new reference system called International Celestial Reference System (ICRS) centered on the Solar System barycenter whose orientation align within 0.02 arcsecond of the Earth mean equator and equinox. The ICRS is connected to the International Terrestrial Reference System (ITRS) via the measurments performed by the International Earth Rotation and Reference Systems Service (IERS).
As said before other coordinates systems exists, but what is mostly used is the equatorial system, for other purposes for example deep space missions is more used the ecliptic system. For all these systems precise transformations exists and are precisely defined by the International Astronomical Union in various publications and supported via well maintained software in Fortran and Python.
For analysis of stellar distribution in the Galaxy another system is used and is called galactic coordinates system, which uses as reference the galactic equator (the big circle corresponding to the maximum emission of the 21 cm emission line of Hydrogen), whose zero point is very close to the radio source Sagittarius A*. These coordinates are called galactic longitude (l: lowercase L) and latitude (b, lowercase B). Is interesting to note that the inclination between the galactic equator and celestial equator, galactic equator and ecliptic, are close to 60 degrees, meaning that the Solar System is higly inclined respect to the fundamental plain of the Galaxy and this creates a helical path as the Sun orbits the Galaxy at 230 km/s, much like Uranus rolls along its orbit around the Sun.
Another system related to the galactic system exist and is called galactocentric rectangular system, in which XYZ linear coordinates (not angles) are calculated from the Galactic Center. Both Galactic coordinate systems are very useful for understand the mass distribution in our Galaxy and to perform cartography of our neighbourhood, however only with the advent of Gaia mission we started to have more precise measurements of the distances of the objects around us.
basic information about the coordinate systems in astronomy
https://en.wikipedia.org/wiki/Astronomical_coordinate_systems
https://en.wikipedia.org/wiki/Equatorial_coordinate_system
a precise definition of the actual reference frames used in astronomy could be found here
https://aa.usno.navy.mil/publications/Circular_179
software libraries
http://www.iausofa.org/
https://docs.astropy.org/en/stable/coordinates/index.html
best regards
Mauro Barbieri
Customer support service by UserEcho
Dear user, thanks for your inquiry.
In astronomy many coordinates systems exists to map the location of celestial objects, that serves different purposes, i.e. to easily manage the data in a more natural framework.
The argument is very vast and cannot be shortly explained in a web ticket, we will provide a brief introduction and some supporting links that could help to understand the big picture.
Like in Earth cartography the definition of a common and uniform coordinate system it has also a long history and there is a strong connection between Earth coordinates and celestial coordinates, and this fact was used by sailors for many centuries for determine their point on open sea, determining the altitude and azimuth of some known stars and Sun and hence determine their position.
But how the coordinates of these stars were and are defined? in ancient times the reference system was based on the ecliptic (the theoretical big circle in the sky) that "contains" the movement of the Sun and the planets, counting the celestial longitude on this circle, and the latitudes as distances from it.
However more recently it was introduced a system, the equatorial system that connect Earth and time to the position of stars in the sky. This system is what is actually used in astronomy. The system is defined in this way:
The big circle corresponding to the projection of the Earth equator on the sky (called the celestial equator), is the reference for the "longitude" that is called in astronomy Rigth Ascension (RA), the perpendicular angular distances to this circle measures the "latitude" that is called Declination (DEC). The zero point of the Rigth Ascension, is measured from the point of the Sun at the equinox of March (i.e. at the intersection of the ecliptic with the celestial equator).
As you can understand, non uniformity on Earth figure, precessional motion, polar motions, all alter this definition.
For creating a fixed reference in space that was not subject to all these problematics, it was created a new reference system called International Celestial Reference System (ICRS) centered on the Solar System barycenter whose orientation align within 0.02 arcsecond of the Earth mean equator and equinox. The ICRS is connected to the International Terrestrial Reference System (ITRS) via the measurments performed by the International Earth Rotation and Reference Systems Service (IERS).
As said before other coordinates systems exists, but what is mostly used is the equatorial system, for other purposes for example deep space missions is more used the ecliptic system. For all these systems precise transformations exists and are precisely defined by the International Astronomical Union in various publications and supported via well maintained software in Fortran and Python.
For analysis of stellar distribution in the Galaxy another system is used and is called galactic coordinates system, which uses as reference the galactic equator (the big circle corresponding to the maximum emission of the 21 cm emission line of Hydrogen), whose zero point is very close to the radio source Sagittarius A*. These coordinates are called galactic longitude (l: lowercase L) and latitude (b, lowercase B). Is interesting to note that the inclination between the galactic equator and celestial equator, galactic equator and ecliptic, are close to 60 degrees, meaning that the Solar System is higly inclined respect to the fundamental plain of the Galaxy and this creates a helical path as the Sun orbits the Galaxy at 230 km/s, much like Uranus rolls along its orbit around the Sun.
Another system related to the galactic system exist and is called galactocentric rectangular system, in which XYZ linear coordinates (not angles) are calculated from the Galactic Center. Both Galactic coordinate systems are very useful for understand the mass distribution in our Galaxy and to perform cartography of our neighbourhood, however only with the advent of Gaia mission we started to have more precise measurements of the distances of the objects around us.
basic information about the coordinate systems in astronomy
https://en.wikipedia.org/wiki/Astronomical_coordinate_systems
https://en.wikipedia.org/wiki/Equatorial_coordinate_system
a precise definition of the actual reference frames used in astronomy could be found here
https://aa.usno.navy.mil/publications/Circular_179
software libraries
http://www.iausofa.org/
https://docs.astropy.org/en/stable/coordinates/index.html
best regards
Mauro Barbieri