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 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.
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