Approximate orbit of the Sun (yellow circle) around the Galactic Centre
The galactic year, also known as a cosmic year, is the duration of time required for the Solar System to orbit once around the center of the Milky Way Galaxy.[1] Estimates of the length of one orbit range from 225 to 250 million terrestrial years.[2] The Solar System is traveling at an average speed of 828,000 km/h (230 km/s) or 514,000 mph (143 mi/s) within its trajectory around the galactic center,[3] which is about one 1300th of the speed of light—a speed at which an object could circumnavigate the Earth's equator in 2 minutes and 54 seconds.
The galactic year provides a conveniently usable 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]
The following list assumes that 1 galactic year is 225 million years.
All the continents on Earth may fuse into a supercontinent. Three potential arrangements of this configuration have been dubbed Amasia, Novopangaea, and Pangaea Ultima[5]
the Milky Way and Andromeda will complete their merger into a giant Elliptical galaxy called Milkomeda or Milkdromeda [9]
500 galactic years from now
The Universe's expansion causes all galaxies beyond the Milky Way's Local Group to disappear beyond the cosmic light horizon, removing them from the observable universe [10]
2000 galactic years from now
Median Point of which the Local Group of 47 galaxies[11] will coalesce into a single large galaxy [12]
Visualisation of the orbit of the Sun (yellow dot and white curve) around the Galactic Centre (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 programme.[13]
^Williams, Caroline; Nield, Ted (20 October 2007). "Pangaea, the comeback". New Scientist. Retrieved 2 January 2014.
^Franck, S.; Bounama, C.; Von Bloh, W. (November 2005). "Causes and timing of future biosphere extinction" (PDF). Biogeosciences Discussions 2 (6): 1665–1679. Bibcode:2005BGD.....2.1665F. doi:10.5194/bgd-2-1665-2005. Retrieved 19 October 2011.
^Luhmann, J. G.; Johnson, R. E.; Zhang, M. H. G. (1992). "Evolutionary impact of sputtering of the Martian atmosphere by O+ pickup ions". Geophysical Research Letters 19 (21): 2151–2154. Bibcode:1992GeoRL..19.2151L. doi:10.1029/92GL02485.
^Quirin Shlermeler (3 March 2005). "Solar wind hammers the ozone layer". nature news. doi:10.1038/news050228-12.
^Cox, J. T.; Loeb, Abraham (2007). "The Collision Between The Milky Way And Andromeda". Monthly Notices of the Royal Astronomical Society 386 (1): 461. arXiv:0705.1170. Bibcode:2008MNRAS.tmp..333C. doi:10.1111/j.1365-2966.2008.13048.x.
^Loeb, Abraham (2011). "Cosmology with Hypervelocity Stars". Harvard University. arXiv:1102.0007v2.
^"The Local Group of Galaxies". University of Arizona. Students for the Exploration and Development of Space. Retrieved 2 October 2009.
^Adams, Fred C.; Laughlin, Gregory (April 1997). "A dying universe: the long-term fate and evolution of astrophysical objects". Reviews of Modern Physics 69 (2): 337–372. arXiv:astro-ph/9701131. Bibcode:1997RvMP...69..337A. doi:10.1103/RevModPhys.69.337.