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Terms in this set (15)

[Observations]
- The Andromeda Galaxy is similar in structure to our own Milky Way
- All planets orbit the Sun in the same direction and nearly the same plane
- More distant galaxies are moving away from us faster than nearby galaxies
- Stars can shine brightly for billions of years


[Explanations]
- The universe is expanding because it began with a Big Bang
- The Andromeda and Milky Way galaxies formed in the same way
- The orderly orbits of planets arose from their formation in a rotating gas cloud
- Stars shine with energy generated by nuclear fusion in their cores



*The distinction between an observation and an explanation is very important in science, but keep in mind that it can sometimes be a bit fuzzy. For example, we have classified the statement "Stars can shine brightly for billions of years" as an observation because we have observational techniques (covered later in your textbook) that allow us to measure the ages of stars; in contrast, although the statement "Stars shine with energy generated by nuclear fusion in their cores" is consistent with many observations, our conclusion that the energy source is fusion depends on our understanding of the physics that should occur inside stars. Note also that our ideas of observation and explanation can change with time. For example, the statement "Earth orbits the Sun" is something we now consider an observed fact, but in the past it would have been considered only one potential explanation for what we see in the sky (and an alternate explanation of "everything orbits Earth" was favored for thousands of years).