The Birmingham age-herald., 1921-02-27

hard to locate on the bright back ground of the sky, but not hard to see when located. Since the planets and their satellites receive the light which they give to us from the sun, they have phases. It is only possible, however, for the planets which are closer Q the sun than the earth, Mercury and Venus and our moon. to have the crescent phase. Mercury and Venus have no satellites. Venus is now of crescent shap, like the new moon Although Venus shows all of the phases like the moon. there are some very great diff ferences, as might be expected, as the motion of Venus is about the sun and that of the moon is about the earth. Some of these differences are these The brightness of body depends both upon its distance from the sun and the earth. Neither of these distances change greatly in the case of the moon. Tho distance of Venus from the sun does not change greatly, but its great est distance from the earth is six times It's least. For this raeson, the apparent Size Is only. sixth as great. The facts are illustrated in Figure 2.
 In position l, when Venus is farthest from the earth, the face illuminated by the sun Is turned toward the earth and Venus Is full" as shown in the open circle. But being in nearly the same oirection as the sun, we cannot see it ana. if we could, 1t would not be very pright, as It is far from us. At g. be- Ing nearer, 1t looks larger, but we can- not See the whole disc, as the whole it. Illuminated face is not turned toward the earth. Venus is then gibbous- that is more than half of the disc is visible At 3, at elongation Venus ap- pears still larger. but only half of the iliumlnate6 side can be seen from the earth. and Venus looks like the quar- ter moon At 4, the illuminated face venus is turned away from the earth, and Venus is new. Near this position, we see a very narrow cres. cent, as shown, but Venus Is then very close to us, so that this crescent is part of a very large disc and hence may be brighter than the full circle at Fl. It happens that Venus, is brightest petween positions and f. when its shape Is that of the moon five days olo. The proportion between the size of the crescent and the full circle at i as drawn, is accurate. When the ,o oon appears in the west, it is waxing moon, but Venus in the same position Is waning as to shape, but not neces- sarfiy in brightness. Conversely in the o"SS III the morning.
 Mercury may be seen in the east be- iore sunrise the last few days of he
 "ontn. By passing opposition March ana will soon supplant Venus as the conspicuous evening star. Saturn sim llarly becomes an evening star March lz. The earth is now on the same side of the rings as the sun, and may be seen as narrow needle of light extending outward from the disc The sun crosses the equator March 20, 10:51 D. m. This marks the beginning of spring.
 it IS announced that Slipher of Low ell observatory has found that a spiral nepula in Cetus is moving away from us with the enormous velocity of 1 1.240 mnes per second. It has been known Tor some time that spiral nebula move with the greatest velocities Cor else we uo)' as great as 500 to 700 miles per second. This is the greatest ve. iocity found anywhere. Why these enormous velocities exist in this oIa .s or bodies is still unexplained.
 BETELGEUX
 Last month we mentioned tha s... that the diameter of one of the star Betelgeux or Alpha Orionis, had been determined. It may be further ex. planned that the diameter of the sun. planet etc, is determined by measur- lng the angle which it's disc subtends. when this angle can be measured ana the distance known, it is easy to cal. cuiate the diameter in miles The stars. however are so far from us that the discs are too small to measure. When Seen through a telescope, stars show a spurfous' disc. due to the diffraction of ngnt, the size of which decreases with larger telescopes. Unless the real disc was larger than this, it's size could not De determineds by ordinary means. Hence, heretofore. we have been unA bie to actually determine the diameter of any star. It has been possible tc calculate the diameter in some cases. such as In eclipsing binaries. Recently the diameters of some of the stars nave been predicted upon the basis of their spectrum and other charac.erfs. ties. Both Eddington and Russell pre- oicted the diameter of Betelreux be. fore the actual measurement with con. siderable accuracy. Both believed it to be a very large star. and this led to the selection of trial star. Other stars suggested as large by Russell are Antares. Aldebaran and Acturus. All are reddish stars. That Bete,geux Is large. Is confirmation of the the. ory of evolution of stars which claims stars are red both near the beginning and end of their existence. For the of this theory. Russell