Local (astronomy)

In astronomy, Local is a term applied to an astronomical object or structure when it is close to an Earth observer, relative to its size. If the scale is large enough to make Earth's distance from the Sun immaterial, the relative closeness of the phenomenon to the star system of the Sun is considered instead.^[1]

Hendrik C. van de Hulst used the following table to describe local objects and structures on varying scales:^[1]

Object	log size (cm)	Beginning of scientific investigations (year A.C.)
Earth	9.1	1500
Solar System	13.2 = 1 AU	1700
Local spiral arm	21.5 = 1000 parsecs	1850-1900
The galaxy	23.0 = 30 kpc
Local clusters of galaxies	24.5 = 3M-lightyears	1930
The universe	28.0 = 10G-lightyears

In the 21st century, the term "local" commonly applies to astronomical groups on five successively larger scales beyond the roughly two-light-year diameter of the Solar System:^[2]

The Local Interstellar Cloud containing the Solar System, roughly 30 light years across
The Local Bubble of gas in turn containing the Local Interstellar Cloud, 300-800 light years across
The Local Arm, a.k.a. the Orion-Cygnus Arm (of the Milky Way galaxy), 3,500 light years wide, and approximately 10,000 long
The Local Group, the group of galaxies that contains the Milky Way, 10 million light-years across
The Local Supercluster or Virgo Supercluster, 110 million light-years across

References

^ ^a ^b H.C. van de Hulst (1965). "Introduction to Astrophysics". In J.G. Emming (ed.). Electromagnetic Radiation in Space. Dordrecht, Holland: D. Reidel Publishing Company. pp. 1–2. Retrieved 27 December 2025.
^ Michel Marie Deza; Elena Deza (2014). "Distances in Earth Science and Astronomy". Encyclopedia of Distances, Third Edition. Springer-Verlag. pp. 559–560. ISBN 978-3-662-44342-2.

This set index article includes a list of related items that share the same name (or similar names).
If an internal link incorrectly led you here, you may wish to change the link to point directly to the intended article.

[:0-1] H.C. van de Hulst (1965). "Introduction to Astrophysics". In J.G. Emming (ed.). Electromagnetic Radiation in Space. Dordrecht, Holland: D. Reidel Publishing Company. pp. 1–2. Retrieved 27 December 2025.

[2] Michel Marie Deza; Elena Deza (2014). "Distances in Earth Science and Astronomy". Encyclopedia of Distances, Third Edition. Springer-Verlag. pp. 559–560. ISBN 978-3-662-44342-2.

[1]

[2]