Photograph of the Great Nebula in Orion, Taken With the Crossley Reflector of the LickObservatoryAuthor(s): J. E. K.Source: Publications of the Astronomical Society of the Pacific, Vol. 11, No. 66 (February 1,1899), pp. 39-40Published by: The University of Chicago Press on behalf of the Astronomical Society of the PacificStable URL: http://www.jstor.org/stable/40671309 .

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NOTICES FROM THE LICK OBSERVATORY.*

Prepared by Members of the Staff.

Photograph of the Great Nebula in Orion, taken with the Crossley Reflector of the Lick Observatory.

The photograph of the Nebula in Orion, which forms the frontispiece of the present number of these Publications, is the first (and possibly the best) of a considerable number of photo- graphs of the same object recently taken with the Crossley 3* foot reflector of the Lick Observatory. The exposure given to the negative was forty minutes, on a fine, clear night when the nebula was only. a little east of the meridian.

The half-tone cut, while not bad as such process illustrations go, does scanty justice to the original negative, which is a very fine one. Only the most expensive processes give satisfactory results in reproducing sirch subjects as this, and even they are much inferior to glass transparencies, which have a far greater scale of intensity. On the original negative the mottled details of the bright Huyghenian region are shown with much perfec- tion, stars are distinct throughout the entire nebula, and the trapezium stars are clearly separated, while loops of faint nebulosity extend beyond the limits of the plate. In the repro- duction these features are practically lost, and there is an abrupt transition of brightness, which is due to a defect of the process.

In exposing and developing the negative the aim was to obtain the best general view of the nebula, and not to show its greatest possible extent. Therefore very full exposure was given, and the development was stopped long before all the nebulosity had appeared which an exposure of forty minutes is capable of showing. In this way, as all photographers are aware, the contrasts between differently bright parts of an image are diminished.

The photographic power of the Crossley reflector on a fine night is surprising, - at least to one who has hitherto worked

*Lick Astronomical Department of the University of California.

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4° Publications of the

with refractors only. In the case of the Orion nebula, the amount of nebulosity shown in the frontispiece is easily obtained with an exposure of five minutes, though at the expense of all detail in the central parts. The Huyghenian and adjoining brighter regions can be photographed in thirty seconds. Com- parison with earlier results obtained with the photographic lens of the great refractor (33 inches aperture) shows that with the Crossley reflector more nebulosity is shown in ten minutes than can be obtained with the refractor in three hours. The great superiority of the reflector indicated by this test is due partly to its much greater angular aperture, and partly to the fact that the thick lenses of the refractor strongly absorb the photo- graphically active rays of the nebula, which, as shown by the spectrum, are largely of quite short wave-lengths.

It should be added that the large mirror of the Crossley reflector has not yet been resilvered. It has been repolished, but the surface is spotted and not nearly as bright as it can be made. J. E. K.

Second Note on the Minor Planet DQ. When the little planet DQ was discovered last August by Dr.

Witt, at the Urania Observatory, Berlin, it was at once noted that its motion was very rapid, thus indicating a marked differ- ence between its orbit and those of the other asteroids. This has been abundantly verified, first by the elements of its orbit computed soon after its discovery by Dr. Berberich, and, later, by those obtained by Messrs. Chandler, Fayet, Hussey, Millosevich, and Russell.

DQ has the shortest periodic time of any asteroid known. While all the others require from 3.0 to 8.4 years to complete a revolution about the Sun, it requires only 643 days, or 1.76 years. In the course of forty-four years it makes very nearly twenty- five sidereal revolutions; so that after this interval it and the Earth occupy again at the same time very nearly the same positions in their orbits, and therefore sustain to each other nearly the same general relations.

The orbit of DQ is to be classed with those having rather high eccentricities. On the average, only one asteroid out of seven has a higher value of this element. On account of the magnitude of its eccentricity, the distance of DQ from the Sun has a range of over 60,000,000 miles, the minimum being a little

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THE GREAT NEBULA IN ORION.

ENLARGE!) 2.3 niAMKTKKS FROM A NEGATIVE MADE WITH THE CROSSLEY REFLECTOR

OF THE LICK OBSERVATORY, ON NOVEMBER 16, 1898.

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