Alex Garcia

September x

Favorite Unit Essay

Period 2 

*_The Galactic Year_* 

The Galactic Year (GY), or cosmic year, is the amount of time it takes
for our solar system to orbit the galactic core of the Milky Way. It’s
estimated to be between 200 and 250 million Earth years. Fitting in
between millions and billions of years, it’s mainly used to measure long
periods of time.

The Galactic Year exists to count periods of time that are already in
millions of years, without the need for large numbers. Our solar system
is thought to be about 20 GY old. The sun was formed in 0 GY, and oceans
first formed on Earth in 4 GY. Life began in 5 GY, with prokaryotes and
bacteria appearing in 6 GY and 7 GY, respectively. The first
multicellular organisms didn’t appear until 16 GY. The first appearance
of modern humans occurred in 19.999 GY, now it is 20 GY.

In addition to Galactic Years, there is also a length of time associated
with a “Galactic Day.” It’s estimated to be about 1/71 of a Galactic
year, but doesn’t have much usefulness as a unit of time. A Galactic
Year is quite a long time, who knows where the human race will be by the
end of the next one.

*Sources:*

http://www.statemaster.com/encyclopedia/Galactic-year

http://www.theorderoftime.com/science/galactic.html

http://en.wikipedia.org/wiki/Galactic_year