Let’s find out what a planet parade is, when it happens and how to see it.
What is a planet parade?Although there is no official scientific term ‘planet parade’, it is widely used in astronomy to denote an astronomical event that takes place when planets of the Solar system line up in a row in the same area of the sky, as seen by observers from Earth. There is no single definition of this phenomenon. These are the three most commonly used:
- An astronomical event that occurs when planets line up in a row on one side of the Sun at the same time, as seen up above the plane of our Solar system. Three planets align on one side of the Sun simultaneously two times a year, four planets – once a year, five planets – once in every nineteen years, and all eight planets of the Solar system – once in about one hundred seventy years.
- A visual phenomenon that occurs when planets of the Solar system appear in a small sector of the sky at the same time regardless of their visibility conditions, from Earth's point of view (as seen by observers from Earth). A planet parade of this type happened on April 18, 2002, when all planets of the Solar system that are visible to the naked eye lined up in a row in the evening sky. According to preliminary forecasts, such planet parades will take place in July 2020, in March and June of 2022, in 2040 and 2854.
- On rare occasions, there are very good seeing conditions of all planets of the Solar system in one night. These events are also referred to as planet parades. For inner planets, the best viewing conditions occur near greatest elongations, and for outer planets – sometime before and after oppositions.