Night sky or good binoculars, the planets appear as discs demonstrating finite size, and it is possible to observe orbiting moons which cast shadows onto the host planet's surface. Venus is the most prominent planet, often called the "morning star" or "evening star" because it is brighter than the stars and often the only "star" visible near sunrise or sunset, depending on its location in its orbit. Mercury, Mars, Jupiter and Saturn are also visible to the naked eye. Earth's Moon is a grey disc in the sky with cratering visible to the naked eye. It spans, depending on its exact location,
Tunnel in the Sky Tunnel in the Sky Tunnel in the Sky is a juvenile science fiction novel by American writer Robert A. Heinlein, published in 1955 by Scribner's as one of the Heinlein juveniles. The story describes a group of students sent on a survival test to an uninhabited planet, who soon realise they are stranded there. The themes of the work include the difficulties of growing up and the nature of man as a social animal. The novel is set in the future, when Malthusian overpopulation on Earth has been averted by the invention of teleportation, called the "Ramsbotham jump", which is