rising

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rising

The daily appearance on an observer's horizon of a particular celestial body as a result of the Earth's rotation, the body disappearing below the horizon, or setting, at some time in the following 24 hours. A star rises, on average, 2 hours earlier per month. Stars always rise and set in the same position relative to other stars whereas the Sun, Moon, and planets rise and set at different points on successive days. This led to the early idea of fixed stars and wandering stars.

For an observer at the equator all stars in theory can be seen, rising and setting at right angles to the horizon. At the poles, only the stars in the observer's hemisphere can be seen, and these never rise nor set but move in circles parallel to the equator. At intermediate latitudes some stars (circumpolar stars) never set and some, in a corresponding area in the sky around the opposite pole, never rise. The remaining stars rise and set at oblique angles to the horizon, the time spent above the horizon depending on the observer's latitude and the position of the star relative to the celestial pole. Stars on the celestial equator rise due east and set due west and for all observing positions except the poles remain 12 hours above the horizon.