Here are some numbers that are useful in getting a feel for distances, speeds, and quantities involved in modelling space.
- Light-year: approx. 9.64*10^18 km
- Astronomical Unit (AU): Distance from Earth to Sun, approx. 150 million km ~ 8.31 light-minutes
Speed of light: 299,792,458 meters/second = 299,792 km/sec
Distance of planets from sun, in millions of km |planet|min|max|Travel time at 1.0c |Mercury|45.9|69.7|3 minutes |Venus|107.4|109|6 minutes |Earth|147|152|8.4 minutes |Mars|206.7|249.1|12 minutes |Jupiter|740.9|815.7|43 minutes |Saturn|1,347|1,507|1.25 hours |Uranus|2,735|3,004|2.5 hours |Neptune|4,456|4,537|4.1 hours |Pluto|7,375|4,425|6 hours
Note these are radial travel times from sun/center to orbital distance. Planet to planet travel times vary dramatically based on relative angular position of the planets in their respective orbits. Minimum travel time is at conjunction (r2-r1), maximum travel time is at opposition (r2+r1). Earth-Mars distance is at minimum about 0.5 AU, at maximum about 2.6 AU, but usually fairly close to 1 AU.
Our galaxy:
- Diameter: approx. 100,000 light-years (perhaps somewhat less)
- Maximum breadth: order of 20,000 light-years
- Our solar system is near the main plane, about 33,000 light-years from the center.
- Takes about 225 million years to complete one revolution -- the 'cosmic year'.
- Contains about 100,000 million stars. Collect them all!