Lucida - the brightest star in a constellation. Lunation - a complete lunar cycle. Magnitude - a measurement of how bright an object is. Meridian - an imaginary line stretching from the north horizon to the south horizon, passing through the zenith. Nebula - a cloud of gas in space.
Some nebulae form stars and some are formed by stars.
North Celestial Pole - a projection of the Earth's North Pole onto the celestial sphere. Open Cluster - a cluster of stars in a galaxy that were formed at approximately the same time in the same area. These stars are not gravitationally bound. Parsec - the distance at which an object must be in order for its parallax shift to be 1 second of arc. Perihelion - a planet's closest point to the sun.