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Galactic year

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Approximate orbit of the Sun (yellow circle) around the Galactic Center

The galactic year, also known as a cosmic year, is the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy.[1] One galactic year is approximately 225 million Earth years.[2] The Solar System is traveling at an average speed of 230 km/s (828,000 km/h) or 143 mi/s (514,000 mph) within its trajectory around the Galactic Center,[3] a speed at which an object could circumnavigate the Earth's equator in 2 minutes and 54 seconds; that speed corresponds to approximately 1/1300 of the speed of light.

The galactic year provides a convenient medial unit for depicting cosmic and geological time periods together. By contrast, a "billion-year" scale does not allow for useful discrimination between geologic events, and a "million-year" scale requires some rather large numbers.[4]

Timeline of the universe and Earth's history in galactic years

[edit]
Main articles: Timeline of the early universe, Timeline of natural history, and Timeline of the far future

The following list assumes that 1 galactic year is 225 million years.

Time Event
Galactic
years
(gal) (approx.) 		Millions of years (Ma) (approx.)
Past (years ago)
61 gal 13725 Ma (13.7 Ga) Big Bang
60 gal 13500 Ma (13.5 Ga) Birth of the Milky Way
49 gal 11025 Ma (11 Ga) A hypothesized merge of Milky Way with Kraken galaxy[5][6]
20 gal 4500 Ma Birth of the Sun and Earth[7]
17–18 gal 3825–4050 Ma Oceans appear on Earth
17 gal 3825 Ma Life begins on Earth
16 gal 3600 Ma Prokaryotes appear
12 gal 2700 Ma Bacteria appear
11 gal 2475 Ma The Great Oxidation Event commences[8]
10 gal 2250 Ma Eukaryian period[9][10] first appearance of eukaryotes[11] Stable continents appear
7 gal 1575 Ma Multicellular organisms appear
5 gal 1125 Ma Meiosis and sexual reproduction appear[12]
4 gal 900 Ma First multicellular terrestrial plants[13]
3 gal 675 Ma Possible early animals (Animalia)[14][15]
2 gal 540 Ma Cambrian explosion occurs
2 gal 500 Ma The first brain structure appears in worms
1 gal 225 Ma Permian–Triassic extinction event
0.3 gal 68 Ma Cretaceous–Paleogene extinction event
0.001 gal 0.23 Ma Emergence of anatomically modern humans
Future (years from now)
0.15 gal 34 Ma Mean time between impacts of asteroidal bodies in the order of magnitude of the K/Pg impactor has elapsed.[16]
1 gal 225 Ma All the continents on Earth may fuse into a supercontinent. Three potential arrangements of this configuration have been dubbed Amasia, Novopangaea, and Pangaea Proxima.[17]
2–3 gal 450–675 Ma Tidal acceleration moves the Moon far enough from Earth that total solar eclipses are no longer possible
4 gal 900 Ma Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible. Multicellular life dies out[18]
15 gal 3375 Ma Surface conditions on Earth are comparable to those on Venus today
22 gal 4950 Ma The Milky Way and Andromeda Galaxy begin to collide
25 gal 5625 Ma Sun ejects a planetary nebula, leaving behind a white dwarf
30 gal 6750 Ma The Milky Way and Andromeda complete their merger into a giant elliptical galaxy called Milkomeda or Milkdromeda[19]
500 gal 112500 Ma (112.5 Ga) The Universe's expansion causes all galaxies beyond the Milky Way's Local Group to disappear beyond the cosmic event horizon, removing them from the reachable universe[20]
2000 gal 450000 Ma (450 Ga) Local Group of 47 galaxies[21] coalesces into a single large galaxy[22]
Visualization of the orbit of the Sun (yellow dot and white curve) around the Galactic Center (GC) in the last galactic year. The red dots correspond to the positions of the stars studied by the European Southern Observatory in a monitoring program.[23]

See also

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The orientation of the Solar System's motion

References

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  1. ^ Cosmic Year Archived 2014-04-12 at the Wayback Machine, Fact Guru, University of Ottawa
  2. ^ Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook.
  3. ^ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA – StarChild Question of the Month for February 2000
  4. ^ Geologic Time Scale – as 18 galactic rotations
  5. ^ Kruijssen, J M Diederik; Pfeffer, Joel L; Chevance, Mélanie; Bonaca, Ana; Trujillo-Gomez, Sebastian; Bastian, Nate; Reina-Campos, Marta; Crain, Robert A; Hughes, Meghan E (October 2020). "Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations". Monthly Notices of the Royal Astronomical Society. 498 (2): 2472–2491. arXiv:2003.01119. doi:10.1093/mnras/staa2452. Archived from the original on November 16, 2020. Retrieved November 15, 2020.
  6. ^ Young, Monica (November 13, 2020). "Star Clusters reveal the "Kraken" in the Milky Way's Past". Sky and Telescope. Archived from the original on November 15, 2020. Retrieved November 15, 2020.
  7. ^ Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Geological Society, London, Special Publications. 190 (1): 205–221.
  8. ^ Buick, Roger (August 27, 2008). "When did oxygenic photosynthesis evolve?". Philosophical Transactions of the Royal Society B. 363 (1504): 2731–2743.
  9. ^ El Albani, Abderrazak; Bengtson, Stefan; Canfield, Donald E.; Riboulleau, Armelle; Rollion Bard, Claire; Macchiarelli, Roberto; et al. (2014). "The 2.1 Ga Old Francevillian Biota: Biogenicity, Taphonomy and Biodiversity". PLOS ONE. 9 (6) e99438. Bibcode:2014PLoSO...999438E. doi:10.1371/journal.pone.0099438. PMC 4070892. PMID 24963687.
  10. ^ El Albani, Abderrazak; Bengtson, Stefan; Canfield, Donald E.; Bekker, Andrey; Macchiarelli, Roberto; Mazurier, Arnaud; Hammarlund, Emma U.; et al. (2010). "Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago" (PDF). Nature. 466 (7302): 100–104. Bibcode:2010Natur.466..100A. doi:10.1038/nature09166. PMID 20596019. S2CID 4331375. Archived from the original (PDF) on June 16, 2024.
  11. ^ F. M. Gradstein (2012). The geologic time scale 2012. Volume 2 (1st ed.). Amsterdam: Elsevier. ISBN 978-0-444-59448-8. OCLC 808340848.
  12. ^ Bernstein, Harris; Bernstein, Carol; Michod, Richard E. (2012). "DNA Repair as the Primary Adaptive Function of Sex in Bacteria and Eukaryotes". In Kimura, Sakura; Shimizu, Sora (eds.). DNA Repair: New Research. Hauppauge, NY: Nova Science Publishers. ISBN 978-1-62100-808-8. LCCN 2011038504. OCLC 828424701.
  13. ^ Strother, Paul K.; Battison, Leila; Brasier, Martin D.; Wellman, Charles H. (26 May 2011). "Earth's earliest non-marine eukaryotes". Nature. 473 (7348): 505–509. Bibcode:2011Natur.473..505S. doi:10.1038/nature09943. PMID 21490597. S2CID 4418860.
  14. ^ Zimmer, Carl (27 November 2019). "Is This the First Fossil of an Embryo? - Mysterious 609-million-year-old balls of cells may be the oldest animal embryos — or something else entirely". The New York Times. Archived from the original on 2022-01-01. Retrieved 28 November 2019.
  15. ^ Cunningham, John A.; et al. (5 December 2016). "The origin of animals: Can molecular clocks and the fossil record be reconciled?". BioEssays. 39 (1) e201600120. doi:10.1002/bies.201600120. PMID 27918074.
  16. ^ Lunar and Planetary Institute (2010), https://www.lpi.usra.edu/features/chicxulub/
  17. ^ Williams, Caroline; Nield, Ted (2007-10-17). "Pangaea, the comeback". New Scientist. Retrieved 2014-01-02.
  18. ^ Franck, S.; Bounama, C.; von Bloh, W. (2005-11-07). "Causes and timing of future biosphere extinction". Biogeosciences Discussions. 2 (6). Copernicus GmbH: 1665-1679. Bibcode:2006BGeo....3...85F. doi:10.5194/bgd-2-1665-2005. S2CID 3619702.
  19. ^ Cox, T. J.; Loeb, Abraham (2008-05-01). "The collision between the Milky Way and Andromeda". Monthly Notices of the Royal Astronomical Society. 386 (1). Oxford University Press (OUP): 461–474. arXiv:0705.1170. Bibcode:2008MNRAS.386..461C. doi:10.1111/j.1365-2966.2008.13048.x. ISSN 0035-8711. S2CID 14964036.
  20. ^ Loeb, Abraham (2011-04-18). "Cosmology with hypervelocity stars". Journal of Cosmology and Astroparticle Physics. 2011 (4). IOP Publishing: 023. arXiv:1102.0007. Bibcode:2011JCAP...04..023L. doi:10.1088/1475-7516/2011/04/023. ISSN 1475-7516. S2CID 118750775.
  21. ^ Frommert, Hartmut; Kronberg, Christine (2007-06-05). "The Local Group of Galaxies". University of Arizona. Students for the Exploration and Development of Space. Archived from the original on 2009-09-07. Retrieved 2009-10-02.
  22. ^ Adams, Fred C.; Laughlin, Gregory (1997-04-01). "A dying universe: the long-term fate and evolutionof astrophysical objects". Reviews of Modern Physics. 69 (2): 337–372. arXiv:astro-ph/9701131. Bibcode:1997RvMP...69..337A. doi:10.1103/revmodphys.69.337. ISSN 0034-6861. S2CID 12173790.
  23. ^ "Milky Way Past Was More Turbulent Than Previously Known". ESO News. European Southern Observatory. 2004-04-06. After more than 1,000 nights of observations spread over 15 years, they have determined the spatial motions of more than 14,000 solar-like stars residing in the neighborhood of the Sun.