Describe the importance/ value/benefit of Astronomy
Clearly describe our place in the cosmos and the universe at various scales
Overview of Astronomy
1/ What is the value/benefit of Astronomy?
Scientific and Technological
Physics Laws; Satellites and Rockets; Materials, etc.
Geography; Time-keeping; Religious Injunctions; etc.
Our place in the Cosmos; Creation; etc.
Astronomical distances and sizes are so large that astronomers use special units Astronomical Unit (AU) – applicable inside the solar system = average distance between Sun and Earth = 150,000,000 km = 1.5 x 10 8 km Light-Year (ly) – applicable between stars and galaxies = distance light travels in one year = ~ 9 x 10 12 km
The Solar System:
The Sun: Our nearby star, at 1 AU = 150 million km away, or just 8 minutes of light travel time, and 100 times the diameter of the Earth; the energy we use on Earth initially comes from nuclear reactions in its core.
Four Small, Rocky Terrestrial Planets
+ asteroids (belt)
Four Large, Gaseous Jovian Planets
+ “Dwarf Planets” : Pluto + Eris + Sedna…
Scale of the Universe and Overview of Contents
Outskirts of the Solar System
Comets: Icy objects, in elliptical orbits. They can enter the inner Solar System and sometimes hit planets.
Stars and Other Things in the Galaxy
Stars: From dwarfs to supergiants; the nearest one is Alpha Centauri, a triple star system at 4.34 ly = 40,000 billion km (~ 300,000 AU), visible from the Southern Hemisphere (only).
Nebulae (clouds) and interstellar matter.
Do those stars have planets? So far, we've found more than 400, and we've just begun (since 1997).
Our “country”: The Milky Way
100,000 light years across, contains ~ 200 billion stars.
A useful analogy: Universe and Earth Geography
City and Neighborhood
Our “city”: The Solar System
Downtown (Sun) and Neighborhoods (Planets).
Other Galaxies and the Rest of the Universe
Other Galaxies: Spiral, elliptical, or irregular.
How many are there? About 100 billion in the visible universe, arranged in clusters and superclusters and moving away from us.
Our neighbor countries:
The Local Group (of ~ 20 galaxies), ~ 3 million light-years across.
The Andromeda Galaxy is our nearest neighbor, about 2 million light-years away.
The Universe is also expanding , everywhere, in all directions, since the Big Bang, and the most recent observations seem to imply that it will probably expand forever…
(More on this later.)
The Universe : A size of ~ 10 23 km!
A “size” of the Universe can be determined from its age and from knowing how fast light travels from one region to another (speed of light = 300000 km/s). The most recent age of Universe (determined in January 2003) is 13.7 billion years...
Graphical Summary of the scale levels of the Universe, from the Earth, to the Solar System, to the Galaxy, to the Universe as a whole! Powers of Ten movie