chapter 1 Flashcards
What is our place in the universe?
Earth is a planet orbiting the Sun. Our Sun is one of more than 100 billion stars in the Milky Way Galaxy. Our galaxy is one of more than 70 galaxies in the Local Group. The Local Group is one small part of the Local Supercluster, which is one small part of the universe.
How big is the universe?
Our galaxy contains more than 100 billion stars—so many that it would take thousands of years just to count them out loud. The observable universe contains more than 100 billion galaxies, and the total number of stars is comparable to the number of grains of dry sand on all the beaches on Earth.
How did we come to be?
The universe began in the BigBang and has been expanding ever since, except in localized regions where gravity has caused matter to collapse into galaxies and stars. The Big Bang essentially produced only two chemical elements: hydrogen and helium. The rest have been produced by stars and recycled within galaxies from one generation of stars to the next, which is why we are “star stuff.”
How do our lifetimes compare to the age of the universe?
On a cosmic calendar that compresses the history of the universe into 1 year, human civilization is just a few seconds old, and a human lifetime lasts only a fraction ofasecond.
How is Earth moving through space?
Earth rotates on its axis once each day and orbits the Sun once each year. At the same time, we move with our Sun in random directions relative to other starsin our local solar neighborhood, while the galaxy’s rotation carries us around the center of the galaxy every 230 million years.
How do galaxies move within the universe?
Galaxies move essentially at random within the Local Group, but all galaxies beyond the Local Group are moving away from us. More distant galaxies are moving faster, which tells us that we live in an expanding universe.
How has the study of astronomy affected human history?
Throughout history, astronomy has developed hand in hand with social and technological development. Astronomy thereby touches all of us and is a human adventure that all can enjoy.
