There are several types of parades of planets, each of which has the features. This astronomical phenomenon, depending on the look, can happen to different frequency.
In a broad sense the term ""parade of planets"" is used for designation of an astronomical phenomenon when three or more planets of the Solar system stand in the row on one side from the Sun. During the small parade are aligned Mercury, Venus, Mars and Saturn, besides occurs this phenomenon annually. The big parade of planets happens slightly less often, but is all the same quite frequent – every twenty years. At this moment to one line six planets of the Solar system are built: Venus, Earth, Mars, Jupiter, Saturn and Uranium. There is still a great parade of planets – an astronomical phenomenon at which all planets of the Solar system (excepting Pluto which was deprived of this status) are aligned on one side from the Sun. As a rule, this phenomenon is considered mystical or even catastrophic, i.e. capable to affect negatively life on Earth, however scientific proofs of it do not exist.
Parades of planets can be both visible, and invisible. Astronomical phenomena of the first type as it follows from the name, assume that they can be observed from Earth. At the same time it is necessary that planets were located in one sector i.e. that the observer could see them from Earth when they are located most closely to each other in the sky. Only the brightest planets of the Solar system participate in visible parades: Mercury, Venus, Mars, Jupiter and Saturn. At the same time the complexity is that Mercury and Venus are disposed closer to the Sun, than Earth, and therefore it is possible to observe them only in the morning or in the evening seasonally and arrangements of the observer.
The parade of planets is of particular importance for astronomers: exactly thanks to it scientists managed to explore in details during the minimum interval of time distant planets of the Solar system by means of spacecrafts. As planets at some point appeared in the narrow sector, to spacecrafts the smallest costs of fuel and time were involved to fly about each of them.