Celestial navigation Celestial navigation Celestial navigation, also known as astronavigation, is the ancient and modern practice of position fixing that enables a navigator to transition through a space without having to rely on estimated calculations, or dead reckoning, to know their position. Celestial navigation uses "sights", or angular measurements taken between a celestial body (e.g. the Sun, the Moon, a planet, or a star) and the visible horizon. The Sun is most commonly used, but navigators can also use the Moon, a planet, Polaris, or one of 57 other navigational stars whose coordinates are tabulated in the nautical almanac and air almanacs.
Polar body polar body can induce the formation of an aneuploid polar body. Therefore, the formation of the first polar body is an especially important factor in forming a healthy zygote. However, chromosomally abnormal polar bodies are not guaranteed to induce the development of an abnormal zygote. A euploid zygote can be produced if the aneuploidy is reciprocal: one polar body has an extra chromosome and the other lacks the same chromosome (see also uniparental disomy). If the extra chromosome is absorbed into a polar body rather than being passed into the oocyte, trisomy can be avoided. Whether this is a chance