On this episode of Our Island Universe: We peer out into the universe and try to see... what we cannot see.
ShanilVirani, Director of the John C. Wells Planetarium Harrisonburg, VA.
Follow on Twitter as shanilv
Transcript:
In our solar system, the closest planet Mercury whizzes around the Sun once every 88 days. Our own planet takes just over 365 days to make one complete trip around the Sun. Little ol’ dwarf planet Pluto needs 248 years to complete one orbit. Do you see a pattern? The further away you are from the Sun, the longer it takes to make one trip around it.
This is known as Kepler’s Third Law and was discovered in the 16th century. In the mid-20th century, American astronomer Dr. Vera Rubin was studying the motions of stars in nearby galaxies. Just like we observed about planets in our own solar system, Dr. Rubin expected to observe that the further a star was from the center of its galaxy, the slower its speed. But nature had other ideas. In galaxy after galaxy that she studied, what she found was that stars far away from the Galactic center were moving just as fast as the stars closer in. Her conclusion was inescapable: there has to be a tremendous amount of unseen matter — or dark matter — in the outer regions of galaxies where the visible stars are relatively few. How much more stuff is there then what we can see? We now think that about 90% of a galaxy’s mass is made up of this “Dark Matter” and we really have no idea what it is.
Even more incredulous is the observation that atom & molecules — the stuff that you, me, and the rest of the world are made up of — constitute only about 4% of the Universe. The remaining 96% is a combination of “Dark Matter” and “Dark Energy” and we are only now beginning to figure out what the heck this stuff is and what it’s made up of. What a great time to be curious about our Universe!