﻿156 
  ANNUAL 
  KEPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  sun. 
  Several 
  indirect 
  methods, 
  depending 
  on 
  the 
  distribution 
  and 
  

   intensity 
  of 
  light 
  in 
  the 
  spectra 
  of 
  the 
  stars, 
  enable 
  us 
  to 
  estimate 
  

   the 
  diameters 
  of 
  some 
  of 
  the 
  very 
  faint 
  stars, 
  and 
  this 
  confirms 
  our 
  

   expectation 
  of 
  their 
  relatively 
  minor 
  size. 
  One 
  yellowish 
  white 
  star, 
  

   indeed, 
  appears 
  to 
  be 
  no 
  larger 
  than 
  our 
  earth. 
  

  

  3. 
  DENSITIES 
  AND 
  TEMPERATURES 
  OF 
  STARS— 
  THEIR 
  INTERNAL 
  

  

  STRUCTURE 
  

  

  Since 
  there 
  have 
  been 
  found 
  no 
  stars 
  of 
  masses 
  many 
  times 
  

   greater 
  than 
  that 
  of 
  the 
  sun, 
  but 
  a 
  whole 
  class 
  of 
  gigantic 
  red 
  stars 
  

   several 
  hundred 
  times 
  the 
  sun's 
  diameter, 
  and 
  therefore 
  millions 
  of 
  

   times 
  the 
  sun's 
  volume, 
  it 
  follows 
  that 
  the 
  density 
  of 
  these 
  red 
  giants 
  

   is 
  of 
  an 
  order 
  a 
  thousand 
  titiies 
  less 
  than 
  atmospheric 
  adr. 
  The 
  

   study 
  of 
  eclipsing 
  variables, 
  many 
  of 
  which 
  are 
  blue 
  and 
  white 
  stars, 
  

   has 
  also 
  indicated 
  a 
  range 
  of 
  densities, 
  not, 
  indeed, 
  so 
  excessively 
  

   rare, 
  but 
  still 
  of 
  the 
  order 
  a 
  thousand 
  times 
  less 
  than 
  the 
  sun's. 
  

  

  As 
  there 
  are 
  many 
  stars 
  of 
  the 
  greatest 
  similarity 
  in 
  size 
  and 
  spec- 
  

   trum 
  to 
  the 
  sun, 
  we 
  must 
  believe 
  that 
  these 
  approximate 
  the 
  solar 
  

   density, 
  which 
  is 
  one 
  and 
  four-tenths 
  times 
  that 
  of 
  water. 
  Yet 
  this 
  

   is 
  by 
  no 
  means 
  the 
  maximum 
  limit 
  of 
  density, 
  for 
  the 
  companion 
  to 
  

   the 
  brilliant 
  star 
  Sirius 
  has 
  lately 
  been 
  proved 
  to 
  be 
  some 
  sixty 
  

   thousand 
  times 
  as 
  dense 
  as 
  water, 
  or 
  three 
  thousand 
  times 
  as 
  dense 
  as 
  

   platinum 
  ! 
  To 
  add 
  to 
  the 
  astonishment 
  which 
  this 
  statement 
  evokes, 
  

   this 
  star, 
  like 
  all 
  others, 
  is 
  mainly 
  gaseous, 
  and 
  is 
  even 
  in 
  that 
  state 
  of 
  

   great 
  freedom 
  of 
  internal 
  motion 
  called 
  perfectly 
  gaseous. 
  

  

  At 
  ordinary 
  temperatures 
  gases 
  may 
  be 
  compressed 
  in 
  the 
  labora- 
  

   tory 
  far 
  beyond 
  the 
  density 
  of 
  water, 
  but 
  their 
  molecules 
  then 
  occupy 
  

   such 
  large 
  volumes 
  compared 
  to 
  the 
  spaces 
  between 
  that 
  the 
  internal 
  

   motions 
  of 
  highly 
  compressed 
  gases 
  are 
  hindered, 
  and 
  they 
  are 
  no 
  

   longer 
  perfect 
  gases. 
  But 
  at 
  the 
  immense 
  temperatures 
  which 
  pre- 
  

   vail 
  within 
  the 
  stars 
  not 
  only 
  are 
  the 
  molecules 
  disassociated 
  but 
  their 
  

   atoms 
  also 
  are 
  ionized, 
  so 
  that 
  in 
  place 
  of 
  the 
  relatively 
  bulky 
  mole- 
  

   cules 
  the 
  separated 
  electrons 
  and 
  nuclei 
  only 
  remain. 
  These 
  primi- 
  

   tive 
  particles 
  are 
  so 
  excessively 
  small 
  that 
  stars 
  may 
  be 
  compressed 
  

   far 
  beyond 
  the 
  densities 
  of 
  our 
  heaviest 
  solid 
  substances 
  without 
  

   losing 
  their 
  perfectly 
  gaseous 
  qualities. 
  

  

  Thus 
  the 
  interiors 
  of 
  the 
  stars 
  are 
  in 
  the 
  simplest 
  possible 
  condi- 
  

   tion 
  for 
  theoretical 
  studies. 
  Eddington 
  and 
  others 
  have 
  taken 
  full 
  

   advantage 
  of 
  this 
  favorable 
  condition 
  and 
  have 
  worked 
  out 
  so 
  

   thoroughly 
  the 
  relation 
  of 
  pressure, 
  temperature, 
  diameter, 
  energy, 
  

   and 
  constitution, 
  and 
  with 
  such 
  excellent 
  accordance 
  with 
  what 
  can 
  

   be 
  astronomically 
  observed 
  among 
  the 
  host 
  of 
  heavenly 
  bodies, 
  that 
  

   we 
  may 
  be 
  said 
  to 
  know 
  far 
  more 
  of 
  the 
  internal 
  condition 
  of 
  the 
  

   stars 
  than 
  we 
  do 
  of 
  the 
  interior 
  of 
  the 
  earth. 
  

  

  