'Powers of Ten' websites list








Some important numbers


Distance Earth-Moon380'000 km≈ 1 light-sec
Distance Earth-Sun150 · 106 km≈ 10 light-minOrbital Semimajor Axis = 1.0 AU
Distance Earth-Saturn1.2 · 109 km (minimum distance)≈ 1 light-hourOrbital Semimajor Axis = 9.5 AU
Distance Earth-Pluto4.3 · 109 km (minimum distance)≈ 4 light-hoursOrbital Semimajor Axis = 40 AU
Distance to the nearest star (Proxima Centauri)4 · 1013 km4.3 light-years (1.3 pc)270'000 times the distance Earth-Sun
Distance Earth-Galactic centre2.5 · 1017 km26'000 light-years (8 kpc)
Diameter of the Milky Way Disk9.46 · 1017 km≈ 100'000 light-years (30 kpc)
Distance to the Andromeda Galaxy (M31)2.46 · 1019 km2.6 · 106 light-years (810 kpc)
Distance to the Virgo Cluster5.3 · 1020 km60 · 106 light-years (18 Mpc)
Diameter of the known universe1-1.5 · 1023 km 10-15 · 109 light-years



Astronomical distances are often expressed in the time it takes the light, travelling at 300'000 km/sec, to cover them:

1 light-hour = 1.08 · 109 km
1 light-day = 2.6 · 1010 km
1 light-month = 7.8 · 1011 km
1 light-year = 9.46 · 1012 km


The parsec (symbol pc) is a unit of length used in astronomy. The length of the parsec is based on the method of trigonometric parallax, one of the oldest methods for measuring the distances to stars. The name parsec stands for "parallax of one second of arc", and one parsec is defined to be the distance from the Earth to a star that has a parallax of 1 arcsecond (= 1/3600 degree), see the figure below. Conversion: 1 parsec = 3.26 light-year = 3.086 · 1013 km (1 Mpc = 103 kpc = 106 pc).

  Credit: Wikipedia.




The solar system: relative sizes



  Credit: Solar system Lithograph Set, NASA

  Source: http://www.rense.com/general72/size.htm