Chapter 1 Our Place in the Universe Chapter Outline Our Modern View of the Universe The Scale of the Universe Spaceship Earth 1/25/2006 1:12 PM Why is the universe comprehensible? What does comprehension of the universe have to do with Darwinian survival of the fittest?
Our Modern View of the Universe
The Scale of the Universe
1/25/2006 1:12 PM
A. What is our place in the universe?
B. How did we come to be?
C. How can we know what the universe was like in the past?
D. Can we see the entire universe?
A moderately large object which orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition.
Self-gravitating, self-luminous spheres of gas, composed primarily of hydrogen, that generate heat and electromagnetic radiation through thermonuclear fusion.
Typical large galaxy contains hundreds of billions of stars, and the universe contains hundreds of billions of galaxies.
Andromeda Galaxy, 2.5 million light years
Galaxies like our Milky Way recycle matter: Stars form from clouds of gas and dust, and stars return matter to the interstellar medium when they die.
Stars form from collapsing clouds of gas and dust, and planets may form in the spinning disk that surround them.
In less than a billion years after the Big Bang, gravity caused matter to collapse into galaxies and clusters of galaxies as spacetime in the universe expand.
Earth formed from hydrogen chemically enriched by heavier elements that result from the death of massive stars.
Stars generate radiant energy by thermonuclear fusion of light elements into heavy elements and massive stars scatter these new elements back into space when they die.
A. How big is Earth compared to our solar system?
B. How far away are the stars?
C. How big is the Milky Way Galaxy?
D. How big is the universe?
E. How do our lifetimes compare to the age of the universe?
A. How is Earth moving in our solar system?
B. How is our solar system moving in the Milky Way Galaxy?
C. How do galaxies move within the universe?
D. Are we ever sitting still?
Earth rotates about an internal axis. Depending on the distance from the axis of rotation, the surface is moving at a rate dependent on its latitude.
Earth’s axis of rotation sweeps through space describing a cone, like a spinning top.
Because Earth’s orbit is elliptical, its distance from the Sun varies over the orbital period. Also, Earth’s axis of rotation is inclined to the orbital plane by 23.5o.
The Sun moves relative to nearby stars and thegroup of nearby stars orbits the center of our Galaxy.