Page images
PDF
EPUB
[blocks in formation]

Photographing the corona, 2 Figs...........

Miller, E.-Corona of the Sun without an eclipse..

Neptune and Mars in 1900, Apparent paths of—..

Orbit of an Algol variable, Circular-Plate IV, opposite.. of a variable, Elliptic-H. C. Wilson.......

[merged small][merged small][ocr errors][merged small]

Planets and stars in the vicinity of the eclipsed Sun........

Potsdam, New photographic telescope of the Astrophysical Observatory at

80

38

113

115

448

526

520

144

..... 447

53

251

[blocks in formation]

Saturn, Uranus and Jupiter in 1900, Apparent paths of—.

..341, 392 39

Saturn's satellites.......

..341, 392

Spiral nebula in Canes Venatici, The great-Plate II, opposite.......

4

spot curve, W. A. Crusinberry........

SS Cygni, Maximum of-....

Stars in vicinity of the Sun, May 28, 1900..........

Sun, Photograph of May 18, 1894, Plate III..

Swift, Dr. Lewis, Photographic search for intra-mercurial planets.......
Telescope of the astrophysical Observatory, New photographic-Plate I.......
Total eclipse of the Sun May 28, 1900......

Total solar eclipse, B. A. A. station (Wadesboro, N. C.), Plate XV, opposite. 369
St. Louis university station (Washington, Ga.), Plate
XV, opposite..........

46

243

57

162

218

1

241

369

Station at Wadesboro, N. C., Plate XVI, oppposite......... 372

U Ophiuchi, Light curve of-H. C. Wilson......

124

Uranus, Saturn and Jupiter in 1900, Apparent paths of-..

39

Variation in Latitude, J. K. Rees, Plate VII, opposite.......

172

Wauschoff zenith telescope at Columbia university Observatory, J. K. Rees,

[blocks in formation]

Whitin Observatory of Wellesley college, Plate XIX, opposite.........
Wilson, H. C., Meteors charted (Andromede)..

467

50

Zodiacal light in Leo, A. E. Douglass, Plate VIII, opposite.......

176

[merged small][graphic][merged small][merged small][merged small]
[blocks in formation]

Besides the Moon, we know that there must be countless much smaller bodies constantly circling about the Earth, in various directions and at various distances. Owing to collisions, and attractions of the Sun and Moon, some of these bodies are occasionally drawn from their normal orbits and precipitated upon the Earth as meteorites. Those that continue to circulate in direct closed orbits, nearly parallel to the plane of the ecliptic, must all, drawn by tides which they themselves produce, gradually recede from the Earth. When they have receded to something over one million miles their periods of revolution will be just one year, and as soon as they recede beyond that point they will be left behind by the Earth in her orbit, and lost to her as satellites. Henceforward they will be dependants upon the Sun. As they approach this limiting distance, however, their rate of recession will become slower, and accordingly a large proportion of them will be found at about this distance from the Earth, and with periods of about a year.

Any meteorite whose period is just one year will remain at a constant difference of longitude from the Sun. As its period approaches this figure it will be much perturbed of the Sun, and rapidly change its longitude with regard to it, save in one position, that where it is in line with the Earth and Sun, and beyond. the former. Here the perturbations will be slight, and consequently the change of position slow, and therefore there will be a greater number of the meteorites collected in this place. In this place, moreover, since they will appear full as seen from the Earth, they will appear at their brightest.

It is therefore suggested that we have here a possible explanation of the Gegenschein, which according to this hypothesis would be an actual body attendant upon the Earth; in short, a sort of cometary or meteoric satellite. Its mass would be small, but its bulk as judged from its angular dimensions would be great, being not far from that of the planet Jupiter.

No meteorite whose period of revolution was one year could remain in line between the Sun and Earth, as it would be drawn away by the former body. There seems to be no question but that some action such as that above described must take place, and therefore that the light of the Gegenschein must be due in part, at least, to this cause, the only question is whether it is wholly due to it; in other words, whether the suggested explanation is adequate to produce the effect observed. A suggestion that the Gegenschein might he of meteoric origin was made by Professor Searle in 1882 (A. N. C II. 266).

It may be pointed out if this hypothesis is correct, that the Moon should produce some effect upon the location of the Gegenschein. Thus, when the Moon, is full the Gegenschein should be slightly to the west of its mean position, and when the Moon is new, it should be somewhat to the east of it. In an article printed for private distribution, but taken in part from POPULAR ASTRONOMY for 1897, Vol. V., p. 178, Mr. Douglass gives the results of an examination of 254 observations of the Gegenschein made chiefly by himself, and concludes that the longitude of the Gegenschein does bear a definite relation to the lunar month. He finds "that observations made before new Moon have a tendency to place the Gegenschein farther east than those made after." Should these observations be confirmed, there would seem to be no doubt that the Gegenschein is a material object attending the Earth in its orbit, and not merely an electrical discharge or a phenomenon produced by remote bodies outside of the orbit of Mars.

HARVARD COLLEGE OBSERVATORY,

December 8, 1899.

THE EULER-LAMBERT EQUATION FOR PARABOLIC

MOTION.

ASAPH HALL.

FOR POPULAR ASTRONOMY.

It is well known that the important equation between the time of moving through the arc of a parabola, the two radii vectores, and the chord, was given first by Euler, although for many years it was known as Lambert's equation. This formula. was published by Euler in the Memoirs of the Berlin Academy, 1743. It is given in his work on the orbit of the Comet of

« PreviousContinue »