Looming and similar refraction phenomena

Depending on atmospheric conditions, the objects can appear to be elevated or lowered, stretched or stooped.

One of the most famous looming observations was made by William Latham in 1798, who wrote: I could very plainly see the cliffs on the opposite coast; which, at the nearest part, are between forty and fifty miles distant, and are not to be discerned, from that low situation, by the aid of the best glasses.

[3]Thomas Jefferson noted the phenomenon of looming in his book Notes on the State of Virginia: There is a solitary mountain about 40 miles off, in the South, whose natural shape as presented to view there, is a regular cone; but, by the effect of looming it sometimes subsides almost totally into the horizon; sometimes it rises more acute and more elevated, its top flat, and as broad as its base.

[4]He was unable to explain this phenomenon and did not think refraction could account from the perceived changes of shape of the object in question.

Looming was sometimes responsible for the errors made by polar explorers; for example, Charles Wilkes charted the coast of Antarctica, where later only water was found.

Towering and stooping are more complex forms of atmospheric refraction than looming and sinking.

The apparent stretching and shortening of the objects are not symmetrical and depends on the thermal profile of the atmosphere.

As the image shows, the different refraction phenomena are not independent from each other and may occur together as a combination, depending on atmospheric conditions.

[2] If, now, the density of the air at the place in question decreases with increase of elevation, as it nearly always does, the upper portion of the wave front will travel faster than the lower, and the path will be bent down towards the earth along a curve whose radius depends upon the rate of this density decrease.

It is conceivable, therefore, that the size of a planet and the vertical density gradient of its atmosphere might be such that one's horizon on it would include the entire surface—that he could look all the way round and, as some one has said, see his own back.