Gusa hari ubwo ushobora gutegereza ko ubona umwijima ugaheba. Imirasire y’Izuba igakomeza kumurikira agace uherereyemo, ku buryo saa Sita z’ijoro zigera ukeka ko ari nka Saa Kumi n’Imwe z’umugoroba.

Ni byo abashakashatsi bita ‘polar day’, ‘white night’ cyangwa ‘nightless night’, bisobanuye ijoro rikeye (ritagira umwijima).

Ibi biba mu bice biri kure cyane y’Umurongo ugabanyamo Isi kabiri (Equateur) biri ku mpera z’Isi byitwa “polar regions”.

Usanga byiganjemo urubura kubera ubukonje buhaba, buterwa no kuba Izuba ridakunze kuhagera cyane.

Ku wa 21 Kamena, Izuba rihamurika amasaha 24 yose mu gice kimwe. Uwo munsi ntirijya rirenga. Ni mu gihe ku wa 21 Ukuboza ho ritahamurika, amasaha 24 agashira hari umwijima.

Uko kubona Izuba cyangwa umwijima amasaha 24 yose, bituruka ku rugendo Isi ikora izenguruka Izuba.

Isi yizengurukaho inshuro imwe mu masaha 24 abarwamo umunsi umwe, ikazenguruka Izuba inshuro imwe mu minsi 365 ibarwamo umwaka umwe.

Mu gihe izenguruka Izuba, hari ingaruka bigira ku bice bimwe na bimwe byayo bishingiye ku gihe. Nko ku wa 20 Werurwe no ku wa 22 Nzeri, habaho kureshya k’umunsi n’ijoro (equinox).

Muri uko kuzenguruka Izuba ni nabwo habaho igihe igice kimwe cy’Isi kiba kitagerwaho n’Izuba, ikindi rikigeraho byeruye (solstice).

Hagati yo ku wa 20 no ku wa 22 Kamena, ni bwo igice cya ruguru (northern polar region) kimara amasaha 24 kimurikirwa n’Izuba, icy’ Epfo (southern polar region) kikamara ayo masaha yose mu icuraburindi.

Nyuma y’amezi atandatu yuzuye, hagati yo ku wa 20 no ku wa 22 Ukuboza, igice cy’ Epfo ni cyo kimara amasaha 24 kimurikiwe n’Izuba, naho icya Ruguru kikayamara mu icuraburindi.

Ahantu ushobora kubonera “white night” ni muri Norvège, Iceland, Greenland, Finland, Suède, u Burusiya, Alaska na Canada.

Aha ni muri Norvège, Izuba ryavaga mu ijoro