Definition of "midnight sun"

He has only retained three engravings; namely, a map of the country, which is very little known, from Torneo to North Cape; a View of Torneo by the midnight moon; and a View of North Cape by the midnight sun.

1806 November, “Observanda Externa [Lapland. North Cape.]”, in The Literary Panorama. […], volume I, London: Printed by Cox, Son, and Baylis, […] for C. Taylor, […], published 1807, column 414

Locked icebergs splintering through the awful night; / And quenchless midnight suns with their wild scarlet light.

1856 August 28, Alfred B[illings] Street, Science: A Poem Dedicated to the American Association for the Advancement of Science, Albany, August 28, 1856, Albany, N.Y.: Van Benthuysen, printer, […], page 6

This wonderful midnight sun has a peculiar effect on the polar vegetation. Although the foliage of ligneous plants, such as shrubs and trees, which here sink down to the condition of dwarfs, is tough and coriaceous, and of a dark and sombre green, gloomy as the long night of the polar world, yet in the steady light which comes from the sun as he circulates above the horizon for weeks, that sombre green tint of the foliage is beautifully softened in the grasses and other herbaceous plants.

1863 January 3, “The Sleep of Plants”, in William, Robert Chambers, editors, Chambers’s Journal of Popular Literature, Science and Arts, volume XIX, number 470, London, Edinburgh: Printed and published by W. & R. Chambers, […], pages 15–16

But when we come to the winter solstice, we get no more midnight suns: as shown in the figure, all the circle is situated in the shaded portion; hence, again in spite of the Earth's rotation, we cannot get out of the darkness, and we do not see the Sun even at noonday.

1868, J[oseph] Norman Lockyer, “Lesson XII.—The Earth’s Movements. Rotation. Movement Round the Sun. Succession of Day and Night.”, in Elementary Lessons in Astronomy, London: Macmillan and Co., paragraph 171, page 70

Like the seasons, the "Midnight Sun" has its origin in the inclination of the earth's axis during its annual motion. […] The effect of this inclination is to produce variations in the length of the day to such an extent, that in polar regions the duration of sunlight is reckoned in months instead of hours.

1894, J[oseph] Norman Lockyer, “The Midnight Sun”, in Spitzbergen and Norway in August 1894: Pleasure Cruise to the “Land of the Midnight Sun” and the Spizbergen Polar Sea, by the Orient Company’s S. S. “Lusitania,” Leaving London August 1st, 1894, London: Sampson Low, Marston & Company, Limited. […], page 61

There are strange things done in the midnight sun / By the men who moil for gold; / The Arctic trails have their secret tales / That would make your blood run cold; / The Northern Lights have seen queer sights, / But the queerest they ever did see / Was that night on the marge of Lake Lebarge / I cremated Sam McGee.

1907, Robert W[illiam] Service, “The Cremation of Sam McGee”, in The Spell of the Yukon and Other Verses, New York, N.Y.: Barse & Hopkins, publishers, page 50