✧ Keystone

  The Keystone is an asterism in Hercules.

                                 ⣀⣠⠤·
                           ⣀⣠⠤⠖⠚⠉⠁  ⢸
                     ⣀⣠⠤⠖⠚⠉⠁        ⢸
                  ·⡚⠉⠁              ⢸
                   ⢧                ⢸
                   ⠈⢧               ⢸
                    ⠈⣇              ⠈⡇
                     ⠘⣆              ⡇
                      ⠸⡄             ⡇
                       ⠹⡄            ⡇
                        ⢹⡀           ⡇
                         ⢳⡀     ⣀⣀⣠⠤⠤•
                          ·⠒⠒⠋⠉⠉⠁

  Type            Asterism
  Constellation   Hercules
  Stars           4

  More information about Keystone

  A keystone is the wedge-shaped block at the top of a stone arch, which
  is roughly the shape these four stars make. None of them is bright, but
  the pattern is worth learning, because a third of the way down its
  western side sits the Hercules Cluster, a ball of several hundred
  thousand stars bound together by gravity. The constellation these four
  belong to is Hercules, which is large, contains no bright star at all,
  and is very hard to find any other way.

  Etymology
  From        English
  Reading     the Keystone
  Literally   the wedge at the top of an arch

  The evolution of Keystone over time

  -50,000 years
  
                                                          ⣀⠤⢴·
                                                     ⢀⣠⠤⠒⠉ ⢠⠇
                                                 ⢀⡠⠴⠚⠉     ⡎
                                             ⣀⠤⠔⠊⠁        ⡸
                                        ⢀⣠⠴⠒⠉            ⢰⠃
                                       ·⡉               ⢀⠇
                                        ⠳⡀              ⡞
                                         ⢣             ⣰⠁
                                          ⢣           ⢠⠃
                                          ⠈⢧         ⢀⡎
                                           ⠈⢆        ⡸
                                            ⠘⡄      ⢰⠃
                                             ⠘⡄    ⢀⠇
                                              ⠙⡄   ⡞
                                               ·  ⣰⠁
                                               ⢸ ⢠⠃
                                               ⢸⢀⠏
                                               ⢸⡜
                                               ⢸⠁
                                               •
  
  now
  
  
  
  
                                                         ⢀⣀
                                                   ⢀⣀⠤⠴⠒⠉⠉⠘·
                                             ⣀⡠⠤⠒⠚⠉⠁       ⡇
                                       ⢀⡤⠴⠒⠊⠉              ⡇
                                        ·⡀                 ⢇
                                         ⢳⡀                ⢸
                                          ⢳⡀               ⢸
                                           ⢳⡀              ⢸⡀
                                            ⢳⡀              ⡇
                                             ⢳⡀             ⡇
                                              ⢳⡀            ⡇
                                               ⢳⡀    ⢀⣀⣀⡠⠤⠤⠔•
                                                ·⠒⠊⠉⠉⠁
  
  
  
  
  
  +50,000 years
  
  
  
  
                                                                     ⢀⣀⣀⢤⡤•
                                                          ⢀⣀⣀⡤⠤⠤⠒⠒⠊⠉⠉⢁⡤⠞⠁
                                               ⢀⣀⣀⡤⠤⠤⠒⠒⠒⠉⠉⠁       ⣀⡤⠊⠁
                                 ⣀⣀⣀⣀⡤⠤⠤⠤⠔⠒·⠒⠉⠉⠁               ⣀⠔⠊⠁
                          ·⡒⠒⠉⠉⠉⠉                           ⡠⠔⠋⠁
                           ⠱⡀                           ⢀⡠⠖⠋
                            ⠱⡄                       ⢀⡤⠖⠁
                             ⠹⡄                   ⣀⡤⠒⠁
                              ⠹⡄               ⣀⠤⠊⠁
                               ⠘⡄           ⣀⠔⠋⠁
                                ⠘⡄       ⡠⠖⠋
                                 ⠈⢆  ⢀⡤⠖⠉
                                  ⠈⠦⠒⠁
                                   ·
  
  
  

  Over 50,000 years either way the longest side of this figure changes by 85%, and the furthest
  any of its stars travels is 12.5 degrees. HR 6220 drifts the opposite way to the other 3,
  which travel together. Proper motion only: this is the shape changing, not the sky turning or
  the pole moving.

  curl 'skymap.sh/Keystone/evolution.gif'

  where it is tonight:  skymap.sh/Keystone