Chapter One Notes

Chapter one notes

                     

·         -The universe is 13,700,000 years old.

·         -Our cosmic address:

-Milky Way= 7 billion stars

·         -Earth is the third star.

·         -Star: a large, glowing ball of gas that generates heat and light through nuclear fusion.

·         -Planet: moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous.

·         -The moon orbits the planets.

·         -Asteroid: a relatively small and rocky object that orbits a star.

·         -Comet: relatively small and icy object that orbits a star.

·         -Solar system: a star and all the material that orbits it, including its planets and moons.

·         -Nebula: cloud of gas and dust.

·         -Galaxy: a great island of stars in space, all held together by gravity and orbiting a common center.

·         -Universe: sum total of all matter and energy; that is, everything within and between all galaxies.

·         -Big Bang= birth of the universe.

·         -The early universe contained only 2 chemicals: hydrogen and helium. All other elements were made by stars and recycled from one stellar generation to the next within galaxies like our milky way.

·         -Life cycles of stars: Many generations of stars have lived and died in the Milky Way.

·         -Light travels at a finite speed (300,000 km/s)

Moon to the earth= one second

Sun to the earth= eight minutes

Sirius to the earth= eight years

Andromeda galaxy to the earth= two and a half years.

·         -Light year

Distance light can travel in one year.

About ten trillion kilometers (6 trillion miles)