Earth's Place In the Observable Universe
- The Moon revolves around the Earth every 27.32 days.
- The Earth-Moon System revolves around the Sun every 365.242 days (1 year).
- It takes the Sun about 230 million years to make one complete orbit around the center of our Milky Way Galaxy (traveling about 828,000 km/hr). Our galaxy is about 100,000 to 120,000 light-years in diameter and contains over 200 billion stars. Our Solar System resides roughly 27,000 light-years away from the Galactic Center.
- The Observable Universe is the part of the greater universe that can be observed by the naked eye or by modern telescopic methods. The light we observe from object in space has travel great distances (measured in light years). This means that distant objects in deep space we see on Earth today have long since changed or moved (Figure 1.41). What is beyond the Observable Universe is unknown.
Figure 1.41. Earth's place in the Observable Universe.