The Birmingham age-herald., 1906-12-02

 star too faint to be seen in smaller tele- scopes, yet once every eleven months in- creases so greatly in brightness that it becomes one of the conspicuous stars of the sky. Neither of these stars attain their maximum brightness this month. If the reader wishes to observe a variable star he may examine the star in Gemini marked H Fig. 1. This will attain it's maximum brightness on December 20 at D. m., and on December 30 at il p. m.; the interval which elapses between the time of greatest and least brightness is five days. As the total change in this star is only about one magnitude, it's va riation is not very conspicuous and can only be clearly detected by comparing the star II with a nearby star. A very con venient star for this purpose is the star at K. At the times above given when the star II is at it's brightest, it Is slightly brighter than K, but at all other times it is quite perceptibly fainter.
 The observation just described is a del icate one. It is not probable that the slightest changes of this nature which oc- cur in the stars would ever attract tho attention of any except the most interest," ed and careful observers. But to one who has convinced himself by observation that the brightness of some of the stars is rapidly changing, the effect Is very striking.
 Causes of Variability.
 What it Is that causes these changes we do not know. We know that the stars are suns. and it is possible that the changes in brightness may be due to the periodical recurrence of spots on their surfaces similar to the spots on our own sun, but on a much more extensive scale. Or the enormous gaseous globules may be subject to periodical eruptions of ma terial from their inconceivably hot interi- or. These eruptions may be caused by the presence of a second dark body which revolves around the sun in a narrow orbit and therefore periodically approaches near to and recedes from it. At the time of its nearest approach it's great attraction or pull on the bright sun may. distort the latter and thus cause brilliant eruption. But with those variable stars of which the light is suddenly cut off at regular intervals we know that the explanation lies merely in the fact that they are at tended by dark companion which al in- terVals comes between the star and us. thus cutting off it's light. Such star is Algol, the Demon Star at l. Fig. 1, which at the regular interval of two days, twen- ty-one hours, has fiye-sxths of it's light suddenly cut off.
 THE PLANETS.
 Mercury is farthest from the sun on De- cember IS, when it may be detected in the southeast one hour before sunrise.
 Venus on December rises one-half hour and on December 3l three hours before the sun. It is in conjunction with Mer- cury on December 13.
 Mars is also a morning star. It may be seen in the constellation Virgo about o'clock.
 Juniper and Saturn are very conspicu- ous in the evening sky, and are in excel lent position for observation.
 The position of Neptune is shown In Fig. 1. With a small telescope this plan ct looks like faint star, and can be iden- tifed only by it's movement from night to night
 The New Comet.
 On November 10 a new comet was dis covered in the constellation Cancer at the point marked c Fig. 4. It was nearly midway between the stars A and B, but was rapidly moving southeast in the di- rection shown by the arrow. The comet is not visible to the naked eye, but may readily be seen in a small telescope to- ward midnight These telescopic comets appear as shown in Fig. :. They arc round woolly-looking objects, without any trace of the tail which is usually so con- spicnous a feature of the brighter com cts
 When further measures have been made, it will be possible to predict exactly how the comet is moving and to mark it's po- sition among the stars on each night. If it is approaching the earth it may during the next few months become a bright and conspicuous object, but if 1t is receding it will grow rapidly fainter and soon be lost to view even in the largest telescopes. Fla. 3-TeIescopic view of Jupiter. The
 bands which encircIe the planet are
 of a delicate rose color, and may now
 be very clearly seen.