SECTION IX - BRILLIANCY OF COMETS

Summary

Estimations of the apparent dimensions or brilliancy of comets–Ancient comets said to be brighter than the sun–Comets visible to the naked eye and comets seen at noonday; great comets of 1744 and 1843.

We will now enter into some particulars respecting the dimensions of comets, their atmospheres, nuclei, and tails. In order to form correct notions concerning this portion of our subject, it is important to distinguish between real and apparent dimensions. This is elementary, but it is here even more necessary than elsewhere, because, from the very nature of cometary orbits, the comet itself, whether periodical or nonperiodical, may be situated at the moment of its appearance either very near to or very far from the earth; so that on two successive apparitions the same comet may appear of very different aspect and dimensions, and at one time may present itself as a very conspicuous body in the sky, at another may be hardly visible, or perhaps not visible at all without the aid of a telescope. We have already alluded to this point when speaking of the difficulty of recognising the identity of a new comet with one before observed by its external aspect; and we must here call attention to it again, when we are comparing different comets in respect to their dimensions, either real or apparent.