﻿ACCOMPLISHMENTS 
  OF 
  MODEEN 
  ASTRONOMY 
  

  

  By 
  C. 
  G. 
  Abbot 
  

  

  [With 
  11 
  plates] 
  

  

  It 
  is 
  natural 
  to 
  ask 
  such 
  questions 
  as 
  the 
  following 
  : 
  

  

  1. 
  How 
  many 
  stars 
  are 
  there 
  and 
  how 
  are 
  they 
  arranged? 
  

  

  2. 
  How 
  far 
  away 
  are 
  the 
  stars 
  and 
  how 
  large 
  ? 
  

  

  3. 
  What 
  do 
  we 
  know 
  of 
  the 
  constitution, 
  age, 
  and 
  source 
  of 
  energy 
  

   of 
  heavenly 
  bodies, 
  and 
  what 
  relations 
  hold 
  regarding 
  their 
  tem- 
  

   peratures 
  and 
  the 
  rays 
  they 
  constantly 
  emit? 
  

  

  4. 
  Whither 
  and 
  hoAv 
  fast 
  are 
  the 
  heavenly 
  bodies 
  m.oving? 
  

  

  5. 
  What 
  is 
  the 
  bearing 
  of 
  astronomical 
  discovery 
  on 
  the 
  province 
  of 
  

   life? 
  

  

  There 
  are 
  many 
  other 
  interesting 
  astronomical 
  questions, 
  but 
  a 
  vivid 
  

   impression 
  of 
  the 
  greatness 
  of 
  the 
  accomplishments 
  of 
  recent 
  years 
  

   will 
  come 
  from 
  a 
  survey 
  of 
  these 
  five 
  alone. 
  

  

  1. 
  NUMBER 
  OF 
  STARS 
  AND 
  THEIR 
  ARRANGEMENT 
  

  

  It 
  was 
  long 
  ago 
  suggested 
  that 
  if 
  the 
  stars 
  are 
  infinite 
  in 
  number, 
  

   and 
  if 
  space 
  is 
  infinite 
  in 
  extension, 
  the 
  whole 
  vault 
  of 
  the 
  heavens 
  

   should 
  glow 
  as 
  brightly 
  as 
  the 
  sun. 
  The 
  interposition 
  of 
  absorbing 
  

   matter 
  would 
  not 
  alter 
  this 
  conclusion, 
  because, 
  according 
  to 
  Kirch- 
  

   hoff's 
  law, 
  the 
  whole 
  interior 
  of 
  a 
  space 
  with 
  walls 
  of 
  constant 
  tem- 
  

   perature 
  takes 
  up 
  the 
  temperature 
  of 
  the 
  walls. 
  Hence 
  absorbing 
  

   matter 
  surrounded 
  by 
  an 
  infinite 
  army 
  of 
  stars 
  would 
  at 
  length 
  be 
  

   as 
  hot 
  as 
  they. 
  

  

  Obviously, 
  therefore, 
  the 
  stars 
  are 
  not 
  infinitely 
  numerous 
  and 
  

   they 
  occupy 
  little 
  volume 
  relative 
  to 
  the 
  space 
  in 
  which 
  they 
  lie. 
  

   In 
  order 
  to 
  estimate 
  the 
  numbers 
  of 
  stars, 
  a 
  careful 
  study 
  of 
  the 
  

   numbers 
  brighter 
  than 
  certain 
  magnitudes 
  has 
  been 
  made. 
  First 
  

   of 
  all, 
  however, 
  the 
  scale 
  of 
  brightness 
  required 
  to 
  be 
  standardized. 
  

   Very 
  anciently, 
  some 
  of 
  the 
  brighter 
  stars 
  were 
  called 
  of 
  first 
  mag- 
  

   nitude, 
  others 
  less 
  bright, 
  such 
  as 
  the 
  Pole 
  star, 
  of 
  second 
  magnitude, 
  

   and 
  so 
  on. 
  It 
  was 
  found 
  that 
  the 
  values 
  assigned 
  by 
  these 
  ancient 
  

   estimates 
  could 
  be 
  nearly 
  duplicated 
  by 
  assuming 
  that 
  an 
  increase 
  

   of 
  five 
  magnitudes 
  produces 
  exactly 
  100-fold 
  decrease 
  in 
  apparent 
  

   brightness, 
  and 
  that 
  the 
  logarithm 
  of 
  the 
  change 
  of 
  brightness 
  for 
  

   one 
  magnitude 
  is 
  

  

  ^-^^=0.4000 
  

   5 
  

  

  74906—28 
  11 
  149 
  

  

  