A "sun dog" is an atmospheric optical distortion of sunlight. It is usually only seen when temperatures are well below freezing, the phenomenon is caused by ice crystals in the lower atmosphere refracting sunlight. The refracted sunlight causes a bright spot to appear beside the sun, on either side or sometimes both sides. They appear at around 22° to the left and/or right of the Sun, and at the same altitude above the horizon as the Sun. While they can appear anywhere in the world they are most commonly seen above and below the Arctic and Antarctic circles respectively due to the frequent cold temperatures. Sun dogs are at their brightest when the sun is close to the horizon. In many cultures sun dogs were seen as bad omens, if they appeared in the early fall it was taken as a sign that the coming winter would be cold and harsh.
Lt. Gore's message written in several languages placed in the cairn (the pile of rocks used as a trail marker) is real, the movie shows a copy of the document left there by the real Franklin expedition. It can be easily found online by searching for Franklin expedition cairn document.
Title refers to the character Lieutenant Graham Gore, who leads a sledge party to King William Island in this episode.
While lightning in the distance adds to the drama of the deck scene, lightning is in fact almost never seen in the high Arctic, and never during winter.
Many atmospheric lights are mistakenly called Sun Dogs. But true sun dogs only appear in pairs and only within the minimum deflection of 22 degree halo of the sun. And the plural form is the only correct form.