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In recent decades, light pollution of the night sky has become a burning issue for all humanity. The negative impact of this state of affairs is particularly burdensome for the living organisms such as humans, animals, and plants, as well as for the whole ecosystems. In addition, it has a particularly negative impact on astronomical observations carried out by professional researchers as well as by amateurs. The night sky polluted by artificial electric light makes the observations of faint astronomical bodies very difficult or even impossible. A special type of such faint celestial bodies comprises comets. However, sometimes comets manifest very large, sudden increases in their luminosity called outbursts of brightness. During the outburst of their brightness, there is a chance to record comets, which are normally objects of low brightness. In this paper, we discuss the conditions of observability of comets during their outbursts of brightness in its relation to the light pollution of the night sky. Numerical calculations are carried out for a hypothetical comet belonging to the Jupiter family. The obtained results are consistent with the observations of outbursts of real comets orbiting in the solar system.

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This paper deals with obtaining the maximum size of cometary grains ejected from nuclei of different shapes. Two mechanisms in terms of grain ejection from comets are taken into consideration. The first one is dragging of particles by outflowing gas molecules released by gentle sublimation from the comets. The second one is related with gas jets from the cavities in a nucleus by cometary jet‐like phenomena. We focused on ellipsoidal shapes of cometary nuclei but with different flattening. Calculations have been carried out for a large range of cometary parameters. It has been shown that for fixed mass of the nucleus the maximum size of grains is an increasing function of the nucleus flattening. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)