Planet Parade: What Is It And How Can You See It?

~4 min
Planet Parade: What Is It And How Can You See It?

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:

  1. 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.
  2. 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.
  3. 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.

Very soon, in August 2020, observers will be able to witness this unique type of planet parade. They will have an incredible chance to see all the planets in one night. At the beginning of the month, the elusive planet Mercury will appear in the morning sky. The brilliant Venus will be sitting nearby. The red planet Mars, the distant Uranus and Neptune, all approaching their oppositions, will be well placed for observation, as well as the gas giants Jupiter and Saturn. Even the dim dwarf planet Pluto will offer skywatchers favorable conditions for viewing it due to the upcoming opposition.

Another term for a planet parade is ‘appulse’. The following types of planetary parades are distinguished according to the number of participating planets:

  • Mini planet parade – 3 planets.
  • Small planet parade – 4 planets.
  • Large planet parade – 5 or 6 planets.
  • Great (full) planet parade – all Solar system’s planets (+ Pluto sometimes).

Mini planet parades are not rare events. Three planets can be simultaneously observed in the same part of the sky several times a year.

When do the planets of the Solar system line up?

It is important to point out that planetary alignment during a planet parade should not be taken literally. In reality, planets never align in one perfectly straight line, as usually shown in the pictures. Since the Solar system’s planets do not all orbit perfectly in the same plane and swing about on different orbits in three-dimensional space, they will never be perfectly lined up.

What can be seen during a parade of planets?

By planets’ alignment or parade, astronomers usually mean that planets will appear in the same part of the sky. Sometimes the arrangement of planets in the sky resembles a line, but it's not always the case. Most often, two or three planets form a line in the sky.

Besides, a lot depends on the viewpoint. When planets line up on one side of the Sun, they are not necessarily in the same region of the sky for observers from Earth. Vice versa, when planets are in the same part of the sky from Earth's point of view, they are not necessarily aligned from the point of view of the Sun.

What planet parade is expected on July 4, 2020? How to see it?

According to forecasts, on July 4, 2020, a rare and unique planet parade will take place. All the planets of the Solar system – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune plus the dwarf planet Pluto – will line up on one side of the Sun at the same time. This will be a planet parade of the first type of the three described above. The near-perfect alignment will not occur, as the deviation angle will be quite small.

The last parade of planets of this type occurred in 1982, and the next one is expected in 2161 and 2492. If you would like to check the time of planetary alignment for your location and to easily locate planets on the sky's dome, consult the stargazing app Star Walk 2. Turn the app's notifications on to be notified about the most noteworthy astronomical events in time.

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Image Credit:Vito Technology

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