Abstract
The Near Approach of Eros.—Prof. H. N. Russell gives, in the Scientific American for January, a clear account of the methods being employed for using the present approach of Eros for obtaining improved values of the solar parallax and the mass of the moon. He estimates that fully ten years will be needed for a full discussion of the measures: but there is one source of delay that he has not considered. Several observatories have been co-operating during the past six or seven years in obtaining accurate places of selected stars near the planet's track. But the track diverges appreciably from the predicted one, to the extent of L minute of time in R.A. at the nearest approach. This makes some of the selected stars unsuitable, as being too far from the planet. It will be necessary to select others on the opposite side of the planet to take their place, and these will need to be carefully observed. One precaution that was not considered in 1901 is now being taken. The spectra of the stars have been examined, and those that differ markedly in type from Eros (the spectral type of which resembles that of the sun) will be rejected, owing to the different amount of their refraction by the earth's atmosphere. The article notes that the opposition of 1938, though inferior to the present one, will be much better than that of 1901, which was the best since the planet was discovered in 1898. 1968 will be about equal to 1938, and the next really favourable oppositions will be in 1975 and 2012.
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Our Astronomical Column. Nature 127, 106 (1931). https://doi.org/10.1038/127106a0
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DOI: https://doi.org/10.1038/127106a0