• 1.4 Gm — Diameter of Sun
  Sun
  The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
  
  
• 1.5 Gm — (proposed) Expected orbit from Earth of the James Webb Space Telescope
  James Webb Space Telescope
  The James Webb Space Telescope , previously known as Next Generation Space Telescope , is a planned next-generation space telescope, optimized for observations in the infrared. The main technical features are a large and very cold 6.5 meter diameter mirror, an observing position far from Earth,...
  
  
• 2.19 Gm — Closest approach of Comet Lexell to Earth
  Earth
  Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
  
  , happened on 1 July 1770; closest comet
  Comet
  A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
  
   approach on record
• 3 Gm — Total length of "wiring" in the human brain.
• 4.2 Gm — Diameter of Algol B
• 5.0 Gm — Closest approach of Comet Halley
  Comet Halley
  Halley's Comet or Comet Halley is the best-known of the short-period comets, and is visible from Earth every 75 to 76 years. Halley is the only short-period comet that is clearly visible to the naked eye from Earth, and thus the only naked-eye comet that might appear twice in a human lifetime...
  
   to Earth, happened on 10 April 837
• 5.0 Gm — (proposed) Size of the arms of the giant triangle shaped Michelson interferometer of the Laser Interferometer Space Antenna
  Laser Interferometer Space Antenna
  The Laser Interferometer Space Antenna is a planned space mission to detect and accurately measure gravitational waves from astronomical sources. LISA was originally conceived as a joint effort between the United States space agency NASA and the European Space Agency...
  
   (LISA) planned to start observations in or around 2015.
• 7.9 Gm — Diameter of Gamma Orionis
  Gamma Orionis
  Bellatrix, also known by its Bayer designation Gamma Orionis , is the third brightest star in the constellation Orion, the twenty-seventh brightest star in the night sky, and one of the brightest second-magnitude stars....
  
  
• 9.0 Gm — Estimated diameter of the event horizon
  Event horizon
  In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...
  
   of Sagittarius A*, the supermassive black hole
  Supermassive black hole
  A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
  
   in the center of the Milky Way
  Milky Way
  The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
  
   galaxy

See also