101 meters ~10 light-years~3 parsecs 十光年 Most of the matter we know is formed into stars,spheres of gas nourished by central nuclear fires that often maintain the glow for a very long time.At this point in the journey, with no star nearby,we see the realm of the stars chiefly as a discant background,no differ. ent from the night sky we view from earth.For several frames the star background remains unchanged:The visible stars are strewn so deep in space that these steps are small in comparison.Hence they cause no noticeable shifts m▣P.C▣m
十光年
101mecer ~1 light-year 10 trillion kilometers 光年 Here one central star is brighter than the rest,only because it is so much nearer.That star is the sun.The contrast becween night and day,between the cold glitter of the starry sky and life-giving warmth,is the consequence simply of our planet's location next to onc modest star.Once we have drawn away from the sun,we can recognize that it is one star among many stars,and all distant stars are in some way suns m▣P,C▣m
一 光 年
1014 meters 100 billion kilometers 千亿公里 All the sun's planets circulate within the small square.From earth the planets have always stood out,a few strange bright stars restlessly wandering in a skyful of unchanging pat- terns.Seen here from outside,the planets take on their Copemican aspect;they move around the sun on these nested cllipses,mapped by colored lines. m▣P.C▣m
千亿公里
10r 10 billion kilometers 百亿公里 The paths of the outer planets fill this picture.That strongly tilted orbit belongs to little, awry Pluto.The four others are those of big Neptune,Uranus,Satum,and Jupiter,with their many satellites.Between Jupiter's path and the sun run the inner planets in their smaller orbits.The planets circulate counterclockwise here,all in nearly the same plane which we view at an angle:The planetary system,apart from Pluto,is flat as a rancake. m▣P.C▣m
百亿公里
1012 meters 1 billion kilometers ~7 astronomical units 十亿公里 Enclosed in the path of massive Jupicer,these are the orbits of the smaller earthlike inner planets:Mars,Earth,Venus,Mercury.Another swarm of objects too small and faint to make out without telescopic aid is present as well:Asteroids and meteors ply this darkness in the belt between the orbits of Mars and Jupiter m▣P.C▣m
十亿公里