Gigantic Spaceship - Starship Earth

by Jeanette Cain

You live on a gigantic spaceship that is speeding through the universe: Starship Earth. You are always spinning, so everything seems to be moving in the opposite direction to the sky, and nothing stays in the exact same spot. Because of this, not every one has the same view, or sees the same objects, such as, Australians can never see Polaris (the North star), and the Southern Cross cannot be seen by Europeans. What you see depends entirely on the time and where you are located, but using that information, you can use objects you see in the sky to tell time and locations.

The North star, or Polaris, lies within the Northern Hemisphere, and its height is determined by the distance north of the equator, or latitude. At the equator, Polaris is just visible on the horizon, or 0 degrees above the horizon. At the North Pole, Polaris is directly overhead at 90 degrees North latitude. Star height is measured above the horizon in degrees being 90 degrees from the horizon to overhead. A star that is halfway up in the sky will be 45 degrees, while a star on the horizon will be 0 degrees.

The Southern Hemisphere does not have a central star like the North Pole, rather the Southern Cross is used to find latitude. It is 27 degrees from the celestial south pole, and easily used in April as it seems to be upright in the sky, or in October when it seems to be upside down. To determine a star's height: if the cross is upright, subtract 27 degrees to determine latitude; if the cross is upside down, add 27 degrees to determine latitude.

Longitude is the distance from east or west of a north-south line running through Greenwich, England. Due to Earth's spinning, different places face the Sun at different times, meaning it may be morning in the United States, midday in Europe and a setting Sun in Australia. There are twenty-four main time zones, each being an hour apart, and in any one zone the Sun will be highest in the sky about noon local time. Earth's rotation goes through 360 degrees in 24 hours making 15 degrees in each hour. If GMT (Greenwich Mean Time) in Greenwich is 6:00 pm, then it is 6:00 am at 180 degrees east. If navigators know the time in Greenwich, they can find their longitude.

Spaceship Earth rotates at a steady rate that puts everyone from night into day, then return to night once again. The spinning of our spaceship changes our view of the universe, and after one complete rotation this starship faces the same direction and the stars have returned to their same place-a process that takes 23 hours and 56 minutes, or a sidereal day. Your starship has traveled 2.5 million kilometers along the Sun's orbit and rotated one extra degree being returning to the Sun's exact place in the sky. This is four minutes, and measured relative to the Sun as a solar day, which is 24 hours long.

Sources:

1. Couper, Heather and Nigel Henbest. Space Encyclopedia DK Publishing, Inc.: NY 1999

2. Editors. Secrets of the Universe. International Master Publishing: US. 1999