Epo: We are in a Spiral Galaxy.
Alkina: Tell me more about this spiral galaxy Epo.
Epo: This spiral galaxy, like others, is a flat, rotating disc. It contains a dense mass of stars in its center with new stellar formation in its spiral arms.
Alkina: Amazing. But how big is it?
Epo: This galaxy is 100,000 light-years across.
Alkina: Wow, that sounds big!
Epo: It is. If you were traveling at 200km/hr, it would take you over 500 billion years to go from one end to the other.
Alkina: Incredible. Well, Epo, I think it’s time we get going and see what this galaxy is made of!!!
What does it mean?
Spiral Galaxy – These galaxies are flattened disks with long spiraling arms that extend out from a central core or bulge. In the arms are large amounts of interstellar matter which lead to high rates of new star formation.
One Light-year – The distance that light travels in one year, which is about 10 trillion kilometers. Since light travels so fast, it covers a lot of distance in a small amount of time and because the universe is so large it makes it easy for astronomers to use light-years as a measuring stick.
In human-speak please!
Two-hundred kilometers per hour (200 km/hr) equals about 125 miles per hour, which is considerably faster than the driving speed limit in most parts of the world. To give some sense of scale, an average human lives for about 70 years, the oldest human fossils are about 200,000 years old, dinosaurs went extinct about 65,000,000 years ago, our solar system is about 4,500,000,000 years old and the universe is about 14,000,000,000 years old.
Now compare this to the time is takes to cross Epo and Alkina’s galaxy, which is 500,000,000,000 years traveling at 200 km/hr. Their galaxy, which is just one of the billions of galaxies out there, is very big!
Is that all?
What is a light-year and how is it used? – Click on the link to find out the answer.