November, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



263 



body has the same "albedo," or light-reflecting power, 

 as Uranus, I find that the dark body would shine as a 

 star of t!ie 9th magnitude when at a distance from the 

 sun of 8.68 times the distance of Uranus, or about 

 15,000 millions of miles. Further, assuming that the 

 sun is moving through space at the rate of 11 miles a 

 second (about its probable value), and that tlie dark 

 body is moving directly towards the sun with the same 

 \elocity, we can calculate by the laws of Dynamics the 

 time taken by the two' bodies tO' come together, start- 

 ing with a distance between them of 15,000 millions 

 of miles. The motion for the first few years would be 

 comparatively slow, and, as I have said, the increase in 

 brightness of the dark body would at first be imper- 

 ceptible. To reduce the distance to 12,000 millions of 

 miles would, I find, take about 3.4 years. At the end 

 of 6.7 years the distance would be reduced to* about 

 9.000 millions of miles, and in 9.8 years to about 6,000 

 millions. At tliis distance the brightness of the dark 

 body would increase to about the 5th magnitude, and 

 it would then be distinctly visible to the naked eye. In 

 about 11.8 years the distance would be reduced tO' 4,000 

 millions, and in alxjut 14 years the dark body would 

 reach the orbit of Uranus, or, rather, it would be at 

 the same distance from us as Uranus, for its patii 

 would not intersect the orbit of the planet, as I will 

 .show presently. It would then shine as a star of about 

 — 0.4 magnitude, or a little brighter than Arcturus, 

 and would, of course, attract general attention. After 

 this its distance would rapidly diminish, and its light 

 quickly increase. After about a year from this time it 

 i\ould reach the distance of Jupiter. Its light would 

 then be greatly increased. It would appear as a star of 

 about — 6i magnitude, or about 4 magnitudes brighter 

 than Jupiter at its brightest, and about 2 magnitudes 

 brighter than Venus at her greatest brilliancy. It 

 would then be the brightest object in the heavens, with 

 the exception of the moon, and would be the " observed 

 of all observers." After this its motion would become 

 very rapid, and in about 51 days it would be at about 

 the same distance from the sun that the earth is. From 

 this point my calculations show that the velocity would 

 be very rapid, and if a direct collision took place the 

 sun and dark body would meet in about eight days, 

 the velocity of each body being then over 400 miles a 

 second ! The effects of such a collision may be easil} 

 imagined. Both bodies would be reduced tO' the 

 gaseous slate within an hour, and a stupendous amount 

 of heat would be produced — heat sufficient not only to 

 destroy the earth, but probably most of the planets 

 of the solar system. 



If the dark body approached the sun in a straight 

 line, it could not strike the earth itself or any of the 

 planets, for the direction of tlie sun's motion in space 

 is inclined to the plane of the earth's orbit at an angle 

 of about 60 degrees. The nearest approach of the 

 dark body to* the earth would depend on the time of 

 year at which its collision with the sun took place. If 

 this occurred about the end of December the dark 

 body would not approach the earth nearer than the 

 su{i's distance, but if the collision took place about 

 June 21st I find that the body would approach the 

 earth within about 80 millions of miles. In the latter 

 case its attraction on the earth would be greater than 

 that of the sun, and it would probably draw the earth 

 out of its orbit. In either case, when the collision to' k 

 place, the sun's mass would be suddenlv douljled, and, 

 •according to Professor Young, the earth's orbit "would 

 immediately become an eccentric ellipse, with its 

 aphelion near the point where the earth was when it 



occurred."'' Hut of course this alteration in the 

 earth's orbit wxnild not concern humanity after the 

 earth, and all its inhabitants, had been reduced to 

 ashes. 



It is, of course, possible that the dark body would 

 not approach the sun directly in a straight line, but 

 along an elongated ellipse. In this case it would miss 

 striking the sun, and there would be no collision. But 

 the earth's motion in its orbit would be much disturbed 

 by the powerful attraction of the dark body, and it ij 

 not easy tO' determine what the exact result would be 

 If, however, the body were moving in a sufficiently 

 elongated ellipse to pass inside the earth's orbit, it 

 would probably pass close enough to the sun, to pro- 

 duce a great disturbance in that body, due to tidal 

 action, and a large amount of extra heat would 

 probably be developed. Should the two bodies merely 

 graze each other, an enormous amount of heat would 

 certamly be produced, quite sufficient to cause the 

 earth's destruction. 



The approach of the dark body to the sun would 

 form a magnificent celestial spectacle. When it arrived 

 within the sun's distance from the earth it would, I 

 find, shine with about the same brightness as the moon 

 when full, but with a smaller diameter, and it would 

 rapidly increase in brightness of surface as it ap- 

 proached the sun. It would then — especially if the 

 approach occurred in the month of June — begin to 

 show phases like the moon, and we should have the 

 curious spectacle of two moons in the sky, one some- 

 what smaller than the other ! 



Instead of a dark body of the mass of the sun, we 

 may suppose one very much smaller, say of the size 

 of Jupiter. In this case, the masses being so un- 

 equal, the sun's motion would be much smaller. On 

 the other hand, the dark body would not become visible 

 until it was much nearer to the earth. In the case of a 

 body like Jupiter, say 87,000 miles in diameter, I find 

 that it would become visible as a star of the 9th magni- 

 tude at a distance of about 3A times the distance oi 

 Uranus from the sun, or about 6,000 millions of miles 

 from the earth. If the diameter of the dark body was 

 the same as that of the earth, it would shine as a star 

 of the 9th magnitude at about the distance of Uranus, 

 and in this case it would fall into the sun in about three 

 years. The amount of heat produced by the collision 

 would, of course, be very much smaller than in the 

 cases just considered, but it seems very probable that 

 even a body the size of the earth, moving with such a 

 high velocity, when it struck the sun would produce 

 the most disastrous results to the earth. Such a body 

 may possibly be now approaching us. If only the size 

 of the earth, it might easily escape detection until well 

 within the orbit of Uranus, and we might then have 

 only a few months' warning before the final catastrophe 

 occurred. 



But, it may be asked, is there any star visible at 

 present which might be identical with an approaching 

 dark body? Well, all I can say is, that I have care- 

 fully examined the region round Vega with a powerful 

 binocular field glass, and that at present (.April, 1905) 

 there is no star brighter than the 7th magnitude within 

 five degrees of Vega, which is not perfectly well known 

 to astronomers. A careful examination with a 3-in. 

 telescope, or, better still, a photograph of the region 

 would be necessary before a decided opinion could ne 

 formed on the subject. 



' Maniial 0/ Astioiwiny, p 294. 



