ABSTRACT
The quantitative morphological classification of galaxies is important for understanding the origin of type frequency and correlations with environment. However, galaxy morphological classification is still mainly done visually by dedicated individuals, in the spirit of Hubble's original scheme and its modifications. The rapid increase in data on galaxy images at low and high redshift calls for a re-examination of the classification schemes and for automatic methods. Here are shown results from a systematic comparison of the dispersion among human experts classifying a uniformly selected sample of more than 800 digitized galaxy images. These galaxy images were then classified by six of the authors independently. The human classifications are compared with each other and with an automatic classification by an artificial neural network, which replicates the classification by a human expert to the same degree of agreement as that between two human experts.
ABSTRACT
Distances on the short and long scales of 12 nearby galaxies, one group, and three clusters are compared with recent estimates by independent methods and researchers. All comparisons show a close agreement [within 0.3 magnitude (mag) in the distance modulus (DM)] between the short-scale moduli and the new estimates by others at all distances from the Large Magellanic Cloud [Delta (distance) = 0.05 megaparsec (Mpc); 1 pc = 3.09 x 10(16) m] to the Coma cluster (Delta = 83 Mpc). The mean systematic difference (short - others) is only -0.04 mag with no evidence for a significant Malmquist bias in the short scale. The long scale differs systematically from all the others by about +0.25 mag within the Local Group (DM < 26) and by +1.1 outside (26 < DM < 35). Accidental errors are also much larger in the long-scale moduli (0.5 mag) than in the other two scales (0.1 mag). The mean value of the Hubble expansion ratio for the test objects is
ABSTRACT
At orbit insertion on 14 November 1971 the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than 2 over most of the planet. The only features clearly visible were the south polar cap, one dark, spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters are rimless and have featureless floors that, in the crater complexes, are at different levels. The largest crater within the southernmost spot is approximately 100 kilometers wide. The craters apparently were formed by subsidence and resemble terrestrial calderas. The south polar cap has a regular margin, suggsting very flat topography. Two craters outside the cap have frost on their floors; an apparent crater rim within the cap is frost free, indicating preferentia loss of frost from elevated ground. If this is so then the curvilinear streaks, which were frost covered in 1969 and are now clear of frost, may be low-relief ridges. Closeup pictures of Phobos and Deimos show that Phobos is about 25 +/-5 by 21 +/-1 kilometers and Deimos is about 13.5 +/- 2 by 12.0 +/-0.5 kilometers. Both have irregular shapes and are highly cratered, with some craters showing raised rims. The satellites are dark objects with geometric albedos of 0.05.
ABSTRACT
After a survey of various definitions of the photometric characteristic curve of photographic emulsions, this paper reintroduces a long forgotten photometric parameter, the opacitance omega = opacity - 1 = 10(D) - 1 and describes its application to a characteristic function I = Aomega(n)(n approximately (1/2)), Which is linear in log-log co-ordinates over the whole range of densities of practical interest in photographic photometry. In a special case n = 1 and J = I/A = omega.
