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J3£TWEEN 1888 and 1782 three more objects of the Mira type were noted—Chi Cygni by Kirch. R. Hydrae by Maraldl and R. Leonta by Koch, the periods ranging from 425 to 312 days, and now some twenty of these long-period variables which are visible to the naked eye are known. In 1784 Goodrlcke discovered one with as short a period os five days, and from its name, Delta Cephel. all similar variables have been designated ‘‘Cephelds. They have this remarkable feature that their Intrinsic brightness nt maximum is proportionate to their period, so that when a new Cepheid is discovered, all we have to do is to note how long Its changes take, from which we ran deduce how bright It really Is. Then, by considering the difference between its real brightness and Its apparent brightness, we can calculate Its distance. Cephelds have for this reason been termed “the yardsticks of the Universe,'* and their presence in the Magellanic Clouds, and In the spiral nebulae, has been one of the most Incontrovertible proofs of the astounding distances nt which these objects lie from us. Still another type of vnrlable has a shorter period even than the average Cepheid. ranging round half a day. the cycles proceeding year alter year with clock-work regularity. The standard star of the Cluster- type, as It Is called. Is R R. Lyrae. but tin fortunately none of this class is visible to the unaided eye.PROBABLY all variable stars down to the ninth magnitude have now been gathered in. The first catalogue of such objects, compiled by Plgott in 1788. contained only 12 entries. One made by Argelander In 1844 had 18 Ten years later the list had Increased to 53. By the end of the century about 700 were known. A catalogue of 1927 had 3000 entries, while In the latest, prepared In 1938 by SchneUer. the number has Increased to 6988. The speediest of them all. a faint star in Aquarius, goes through Its phases in 1 hour 28 minutes, the most sluggish. V. W. Aquilae. requires 950 days. In some cases the wavering Is quite Irregular. The average range of brightness In the long period variables Is about from one to one hundred but many greatly exceed this average, one star (Chi Cygni) being known to have an extreme range of 10,000 times. We can only make a compassionate guess at the miserable condition of the Inhabitants (If any) of the planets (If any) which circulate around it. Their feelings at having to put up with a summer temperature ten thousand times hotter than the winter one may be better Imagined than described.grows dim again as the surge subsides.and so on.XOTW JTH8TANDING the substantial catalogue of known variables, It Is Important to keep on looking for more Some day. a lucky observer may happen upon one with such a novel or abnormal type of variability that it will throw a flood of light upon the problem and bring us closer to aknowledge of the nature of themysterious universe to which we belong. It is as likely aa not that the discovery, when made, will bemade by an amaleur. became he withhis small telescope and Inexpensive equipment has u better chance than the busy professional of specialising on the subject, and few persona realise until the)- have tried it out. how fascinating the aearch for these odd the two forces, and the light 1 little changelinga can become,
Newspaper Details
Mackay Daily Mercury
Mackay, Queensland, AU
Sat, Mar 18, 1939
Page 11
Full Page
Clipped by
Chase H.
NA, 06 Mar 2024
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