- The names of various objects are listed in the first column of the table below. Please describe the sizes of these objects using "standard" Earth units (kilometers), and spaceship travel time. The sizes of the objects can be found by browsing through the textbook. For reference, the diameter of the Earth is about 13,000 km, and the diameter of the Sun is 1,400,000 km (1.4X10
^{6}km), a bit more than 100 times the size of the Earth. Spaceship travel times should be described in hours, days, years, centuries; whichever allows the most comfortable numbers---between 1 and 1000 if possible.Object Diameter (km) Diameter (spaceship travel-time) Moon Earth 13,000 km Sun 1.4X10 ^{6}Solar System Milky Way Galaxy Virgo Cluster 1.67X10 ^{19}km - Suppose that during your lifetime, technology improves, and space travel of 100,000 km/hr becomes feasible. At this speed, how long would it take humans to reach Pluto from Earth?
- Suppose someone asks you how far it is from the Earth to the Sun. You could answer "93 million miles", or you could say "8 light minutes". If you know how fast light travels (186,000 miles per second or 300,000 km/s), then the second answer replaces an uncomfortably large number with a more reasonable one.
Distances in the astronomical realm are huge. Using miles or kilometers becomes silly when you are consistently talking about "four hundred million trillion miles". It makes sense to switch to much more reasonable units. The normal choice is the light travel time. Fill in the blanks in the table. Light travel times can be given in light-hours, light-days, or light-years; whichever allows the use of the most comfortable numbers.
Object Distance (km or A.U.) Distance (light travel time) Sun 1 A.U.=1.5X10 ^{8}kmPluto 38 A.U. Nearest Star (not the Sun) Nearest Large Galaxy (M31) 2 Mly = 2 million light years Nearest Cluster of Galaxys