Galactic year
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] According to Nasa, the Solar System is traveling at an average speed of 828,000 km/h (230 km/s) or 514,000 mph (143 mi/s),[3] which is about one 1300th of the speed of light. If you could travel at that speed in a jet aircraft along the equator, you would go all the way around the world in approximately 2 minutes and 54 seconds. According to NASA, even at this incredible speed, it still takes the solar system 230 million years to orbit the center of the Milky Way Galaxy one time.[3]
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 universe's and earth's history in galactic years
The following list assumes that 1 galactic year is approximately 225 million years.
| about 60 galactic years ago | Big Bang |
| about 59 galactic years ago | Birth of the Milky Way |
| 20 galactic years ago | Birth of the Sun |
| 16 galactic years ago | Oceans appear on Earth |
| 15 galactic years ago | Life begins |
| 14 galactic years ago | Prokaryotes appear |
| 13 galactic years ago | Bacteria appear |
| 10 galactic years ago | Stable continents appear |
| 7 galactic years ago | Eukaryotes appear |
| 4 galactic years ago | Multicellular organisms appear |
| 2.8 galactic years ago | Cambrian explosion |
| 1 galactic years ago | Permian–Triassic extinction event |
| 0.4 galactic years ago | Cretaceous–Paleogene extinction event |
| 0.001 galactic years ago | Appearance of modern humans |
| Present day | |
|---|---|
| 6 galactic years in the future | Sun's habitable zone moves outside of the Earth's orbit[citation needed] |
| 10 galactic years in the future | The Milky Way and Andromeda Galaxy begin to collide |
| 30 galactic years in the future | Sun ejects a planetary nebula, leaving behind a white dwarf |
![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.[5]](/wiki/File:Sun_in_orbit_around_Galactic_Centre.gif)
See also
References
- ^ Cosmic Year, Fact Guru, University of Ottawa
- ^ Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook.
- ^ a b http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA - StarChild Question of the Month for February 2000
- ^ Geologic Time Scale - as 18 galactic rotations
- ^ "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 neighbourhood of the Sun.
