Show STAR EXPANDS AND CONTRACTS Mira Varies in Brilliancy Puzzling to Astron Astron- Astronomy Astronomy Astronomy omy Students ll uy By DAVID DD D DAvin D IZ NEA NE E Sen Ice Writer MT IT WILSO WILSON Calif April 9 i A A star tar that apparently expands and contracts not unlike a beat beat- Ing beatIng beat heart has been discovered In the Inthe sk sky ky It Is 15 the blo arla star known to astronomers as Mira Variable stars arc are ones which change their brightness periodically cally catty shining mining with a a strong light at t certain times time and with with a dim light at others Mira was wa the th first variable star ever noted In the th heavens hea The discovery was made In 1596 by Davit l He H named It Mira from the th Latin meaning wonderful But It remained for ter Jr Dr Alfred if H Joy secretary of the Mt Wilson Wll- Wll son on observatory to discover lest jast how wonderful a star lIr l Mira really was TE YE STUDY Dr Joy has just lust completed a ten year year aten-year study of that star Etar bring bring- Ing Ing- Inc bringIng to bear upon the problem the th Inch telescope of tho the Mt Wilson observatory the largest telescope In the world and th the theother theother other marvelously delicate apparatus apparatus atus Mus which Is located at the ob- ob observatory ob observatory Dr Joy painted for or me a word ord picture of o what his hi year ten study lad had revealed The apparent ex- ex expansion expansion ex and contraction of the th star Is If one on of o the th outstanding features when at maximum brightness Mira Is about a second or third magnitude star Dr Joy told me That Is Is It Is among among- the th second brightest or or third brightest class v When if 11 It sinks to Its minimum It becomes entirely Invisible to the naked eye ee The telescope shows that magnitude tude It drops to the ninth magni- magni tude Until the th Inch telescope was built It t was Impossible to tomake tomake male make a spectroscopic study of Mira at Its minimum brightness Much of the new Information which has hils been amassed during thIs year ten-year study of th the star stor was made possible through the tb ability to follow the star stor at Its lis minimum with the aid of the Inch tele- tele telescope tele telescope scope VARYING BRILLIANCY The Th star goes gots through Its 1 van va- va va variations n In n brIghtness In a perIod p of days das It I Is times as bright at maximum as at mini mini- minimum minimum mum In In addition to studying studying- the star with the which en- en enables enables en enables ables one by measuring the lines in the spectrum to compute the stars star's temperature motion compo compo- composition composition and the th like I have enlist enlist- enlisted enlisted ed cd the did aid of some of 01 my col- col colleague colleagues col leagues league here her at the observatory Dr Nicholson and Dr Pease helped check the th temperature with the thermocouple by which they Uley measured the temperatures of the tho planets recently while Dr Pease pleasured measured th stars star's diame diame- diameter diameter diameter ter with the th Michelson Interferometer Interferometer eter IMMENSE The Th study shows that the star Is one of the largest In tn our uni- uni universe universe vers verse It has a diameter of miles It Is composed of ex extremely remely rare gases eases however Its density at the center Is about ten one thousandth one thousandth of the th density of the earths earth's atmosphere while the density of the outer r portions of othis this thle gigantic star Is about one one- ten ten millionth of the earths earth's atmo atmo- atmosphere atmosphere sphere sphere what hat we wo consider a II pretty prelly high vacuum here on earth e-arth In other words this gigantic star In many ways was resembles a nebula except that It has bos the shape of oC II a a star LOW TEMPERATURE TC E A study of the stars star's tempera tempera- temperatures temperatures temperatures tures shows It to be extremely low Our sun has a II temperature at the th surface of of of- CO 00 degrees decrees The Th temperature of this star ranges from 2400 2100 degrees decrees at max max- maxImum maximum down to 1700 degrees decrees at minimum The study also shows that while th the star gives elves three hun hun- hundred hundred hundred dred times less light at minimum than at maximum the amount of heat radiated by the star Is only two and a half times time less at mint minimum mum than at maximum The spectroscope reveals what happens At the tho high hith tempera tempera- temperature temperature temperature ture we vc have many elements such as titanium existing In tn the ato- ato atomic atomic ato atomic mic state slate tate But as the th tempers tempera temperature ture falls this element clement and oth others oth- oth others others ers begin berin to form compounds with the oxygen In the star It It Is Is therefore just lust as though II a veil composed of these the com com- compounds com compounds pounds were drawn dran around the star letting through most of the heat but hut shutting- shutting oft off the light But nut the th most astounding fact Is reveal revealed cd where we use the spec spec- spectroscope spectroscope spec to the thc motion motton of oC th the outer part of the tho star This motion motton changes chances from maxi maxi- maximum maximum mum to minimum brightness and can enn be explained only by supposing that the star starla Is expanding at maximum brIght bright- brightness nes ness nef S and contracting at minimum brightness It apparently con con- contracts contracts con contracts tracts 22 per cent of Its diameter from maximum to to minimum brightness |