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Table giving, in mean time, the approximate limits between which the altitude of Eros above the horizon is greater than 20° for the dates and latitudes indicated.

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Table giving, in mean time, the approximate limits between which the altitude of Eros above the horizon is greater than 20° for the dates and latitudes indicated.

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36... 37...

Nov. 8.

h m h m

Noy. 18.

2.49 16.53

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h m h m

1.40 14.58

1.23 14.13

1.35 15. 3
1.30 15. 8,

1.19 14.17

1.15 14.21

1.25 15.13
1.19 15.19
1.13 15.25
1. 7 15.31
1. I 15.37

44...

2.43 18.57

1.50 17.52

1.14 16.46

45...

2.34 19. 6

1.41 18. I

1. 6 16.54

0.55 15.43
0.49 15.49

1.11 14.25 I. 6 14.30 I. I 14.35 0.56 14.40 0.51 14.45 0.46 14.50

0.46 14. 8

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[blocks in formation]

1.32 18.10

47...

2.14 19.26

1.22 18.20

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0.38 14.16

0.36 16. 2

0.30 15. 6

0.34 14.20

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0.29 16. 9

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[blocks in formation]

0.59 18.43

0.32 17.28

0.21 16.17

0.18 15.18

0.24 14.30

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0.48 18.54

0.22 17.38

0.13 16.25

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[blocks in formation]

0.45 20.55 -0. 1 19.43 0.20 21.20 -0.25 20. 7 -0.28 18.28 -0.24 17. 2 -0.16 15.52 -0.9 21.49 -0.52 20.34 -0.44 18.44 -0.35 17.13 -0.24 16. o -0.9 15. 3 -1.21 21. 3-1. 2 19. 2 -0.46 17.24 -0.33 16. 9 -0.15 15. 9 -1. I 17.39 -0.43 16.19 -0.22 15.16 -1.17 17.55 -0.53 16.29 -0.29 15.23 -1.35 18.13 -I. 4. 16.40 -0.37 15.31 -1.55 18.33 -1.14 16.50 -0.45 15.39

-1.27 19.27
-1.57 19.57

0.5 16.33 o. 6 15.30

0.14 14.40

o. 8 14.46

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SUCCESSIVE POINTS ON THE APPARENT PATH OF EROS, ONE Degree of ARC

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THE PLANET EROS.

W. W. PAYNE.

The planetoid Eros (433) is now occupying the attention of working astronomers more than any other one celestial object.. On this account it will be of interest to many of our readers to have a re-statement of the principal facts about this new planet: It was discovered by Witt of Berlin on August 13, 1898, when it appeared as a star of only the 11th magnitude. Its discovery, however, was not announced by telegraph until Sept. 5, which gave some information of its remarkable orbit which was then known to be in part, at least, within the orbit of planet Mars. An announcement of this discovery promptly appeared in the foreign scientific journals, especially in the Astronomische Nachrichten, No. 3512, in which attention was called to the rapid motion of the planet, which, on the average, was about 2000 seconds of arc daily.

During the same month and under date of Sept. 30, Professor E. C. Pickering of the Harvard College Observatory published a circular, which was numbered 34 in the regular series, setting forth much important information about the new, little planet. From the data then known relating to its path, it was found that its minimum distance from the Earth, where the orbit lies near the path of the Earth, was only 15.000,000 of miles. The importance of this interesting fact will at once appear, when it is remembered that the nearest approach of the planet Mars to the orbit of the earth is about 35,000,000 of miles, and that the Earth and Mars are so related in nearness of position, only once in 15 or 17 years. Since the planet Eros is distant from the Earth, at times of favorable opposition only 15,000,000 it is evident that this planet furnishes a most favorable means for the study of parallax, and astronomers are using the present opposition of the planet as an opportunity for prosecuting work of this kind most vigorously. For those who do not know how the parallax of the planets is determined approximately, it may be said that the parallax of Venus or Mars when nearest is only about 40 seconds of arc, a very small angle to measure accurately. The parallax of Eros is nearly 60 seconds of arc which, of course. is a more favorable angle for measurement on account of its increased size.

Astronomers know very accurately the ratio distances of all the planets in the solar system in units of the Sun's distance.

Now, if the parallax of any one planet can be obtained very accurately then the distance of all will be known, including that of the Sun in miles or other terrestrial units. This is the same old problem that has been before the minds of the students of the heavens since the dawn of the science of Astronomy.

The methods of the New Astronomy offer some advantages in the study of the problem. Photography is being used at a number of the larger observatories. But some difficulties are met in the work on this new planet which act as somewhat of a drawback, in the use of this favorite way of determining the places of the planet at specific times so as to map its path among the stars during the next few months to come. In the Harvard College Circular just referred to it was said that short exposures of Eros could not be used to determine the photographic brightness. of the planet because it was so faint and its motion so rapid. Long exposure could not be used because the planet's trail could not be compared with the circular images of the stars near by to determine the planet's brightness relatively. The point of interest to observers now is can these planet trails on the photographic plates be used to determine the exact places of Eros in reference to adjacent stars, so that measures on the photographic plates may be employed to get the parallax of the planet. If so it will certainly give aid in the prosecution of this work in connection with the measures by the micrometer with visual objectives of a large aperture.

The photographic plan being tried at. Goodsell Observatory with the 84-inch Clark refractor is to make exposures of plates for different lengths of time. The longer exposures to be broken for brief intervals at certain times which will be recorded on the chronograph. From such attempts already made, it seems clear that measures from the beginnings and ends of these trails, as points, may be taken to near stars that may be identified, on the plates, and in this way an accurate place of the planet may be known at the particular time of the observation. How well this plan will work out photographically we are not yet able to say, but we hope for results in a few days, if the nights are favorable.

The work of determining the places of Eros on every clear night by the aid of the micrometer and the 16 inch equatorial is carried forward with much interest and ease. It is not at all difficult to "pick up" the planet in the large instrument because of its rapid motion. By looking at such a chart of the path of Eros as ac

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THE APPARENT PATH OF EROS AMONG THE STARS,
From Sept. 20, 1900, to Jan. 6, 1901.

The positions platted are for the epoch 1855. The precession to 1900 is approximately 3m in R.A. and +12' to 14' in Dec.

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