Positional astronomy
From Wikipedia, the free encyclopedia
Positional astronomy is the study of the positions of celestial objects. This is the oldest branch of astronomy and dates back to antiquity. Observations of celestial objects are important for religious and astrological purposes, as well as for timekeeping. The science of actually measuring positions of celestial objects in the sky is known as astrometry.
The unaided human eye can detect about 6000 stars, of which about half are below the horizon at any one time. On modern star charts, the celestial sphere is divided into 88 constellations. Every star lies within a constellation. Constellations are useful for navigation. If you live in the northern hemisphere you can find north by locating the star Polaris. This star is always at a position nearly over the north pole.
[edit] Positional phenomena
- Planets which are in conjunction form a line which passes through the center of the solar system
- The ecliptic is the plane which contains the orbit of a planet, usually in reference to Earth
- Elongation refers to the angle formed by a planet, with respect to the system's center and a viewing point
- Superior planets have a larger orbit than the earth while the inferior planets (Mercury and Venus) orbit the sun inside the earth's orbit
- A transit occurs when an inferior planet passes through a point of conjunction
