Opposition of the planets: definition, features. What planets can be in opposition?

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Opposition of the planets: definition, features. What planets can be in opposition?
Opposition of the planets: definition, features. What planets can be in opposition?

In positional astronomy, two objects are considered to be in opposition (opposition) when they are located on opposite sides of the celestial sphere, as observed from a third (side) celestial body (usually from Earth).

A planet (or asteroid/comet) is said to be "in opposition" when it is on the opposite side of the Sun. Since most of the orbits of the solar system are nearly coplanar with the ecliptic, this happens when our star, the Earth, and a third celestial body are configured in approximately the same straight line or syzygy. The Earth and this very third celestial body are in the same direction as the Sun. Opposition occurs only at higher planets.

Mars opposition


When viewed from a superior planet, the inferior one on the opposite side of the Sun is in excellent conjunction withher. A low conjunction occurs when two planets coincide on the same side of the Sun. Under him, the highest planet "opposes" the luminary, if viewed from its side.

Role of Mars

Like all the planets in our solar system, Earth and Mars revolve around the Sun. But the first is closer to it, and therefore moves faster in its orbit. The Earth makes two revolutions around the Sun in about the same time that Mars makes one.

So sometimes the two planets are on opposite sides of the Sun, very far apart, and other times the Earth catches up with its neighbor and passes relatively close to it.

Planet opposition: Earth and Mars

During opposition, Mars and the Sun are directly on opposite sides of the Earth. From our perspective of the spinning world, the red planet rises in the east just as the sun sets in the west. Then, remaining in the sky all night, Mars sets to the west just as our star rises in the east.

Because Mars and the Sun appear on opposite sides of the sky, we say that the Red Planet is in "opposition". If Earth and Mars followed in perfectly circular orbits, opposition would be as close as two planets could reach.

Mars observation


Opposition planets, in the case of Mars, occur approximately every 26 months. Opposition occurs within a few weeks of perihelion (the point in its orbit when the planet is closest toSun).

Last year, the opposition of Mars took place on July 27, 2018. It can occur anywhere in the orbit of Mars. When this happens, when the red planet is closest to the Sun (called "perihelic opposition"), it is particularly close to Earth. If the latter and Mars had perfectly stable orbits, then each perihelic opposition would bring the two planets as close as possible. It almost does.

But then again, nature adds a few complications. The gravitational pull of other planets is constantly changing the shape of our orbits slightly. Giant Jupiter especially affects the orbit of the red planet. In addition, the orbits of the Earth and Mars do not lie in the same plane: the trajectories of the planets are slightly inclined relative to each other.

Differences in orbits

Mars' orbit is more elliptical than Earth's, so the difference between perihelion and aphelion is greater. Over the past centuries, the orbit of the first planet has become more and more elongated, moving it even closer to the star at perihelion and even further away at aphelion. Thus, future perihelic oppositions of the planets will bring Earth and Mars even closer.

Earth and other planets in the solar system do not own a certain area in the universe. Without a permanent address in space, they were called wanderers. Positioning has an obvious effect on planetary observations.

Positional astronomy

In it, two celestial bodies are viewed from a certain place, being on opposite sides of the sky. Obviously, two planets are considered opposite to each other ifthere is a relative elongation of the Sun (a measurement of the angle between a planet and a luminary) of 180°, which is considered the maximum elongation. Simply put, the opposition of the planets is when a celestial body is opposite the Sun in the sky of the Earth, or when the latter is located between it and the luminary.

Moon observation

The starting point is always the Sun. The higher planets, whose orbits are outside the Earth, may be in opposition to it. A great time to view the planet is during solar elongation. On the other hand, the lower planets, such as Mercury and Venus, have different elongation periods than the higher ones, which are farther from the Sun than from the Earth.

Other features

When the superior object, the Earth and Sun align in a straight line with our planet between them, this is called opposition. When the superior planet and the Earth lie on opposite sides of the Sun, this is called conjunction. It has been observed that the opposition of some planets makes them closer to Earth, and this will be a good time to observe the higher planet.

Opposition scheme


What planets can be observed at opposition other than Mars? It should be noted, first of all, the largest celestial body of our system. Jupiter is the largest planet and the fifth from the Sun. It is characterized by brightly colored stripes on its surface and a large red spot near the equator.

Jupiter revolves around the Sun with a period of about 11.86 years. In ancient China, the year was counted according to theJupiter on the celestial sphere and corresponded to 12 earthly branches (a cycle of 12 animals). So he is also known as the Star of the Century. Jupiter opposition will occur approximately once every 399 days.

Jupiter is the second brightest planet after Venus. In the weeks before and after opposition, Jupiter is very bright, reaching a visual magnitude of around -2.5. This will be a good time to observe it, its Great Red Spot and its four largest moons, namely Io, Europa, Ganymede and Callisto. A telescope with a magnification of 40 times or more is preferred when viewing Jupiter.

Moon and Opposition

Visual value

It is a measure of the brightness of a celestial object. The visual magnitude of a faint star is large and positive. The brighter it is, the smaller the visual value will be. The brightest celestial objects will have negative magnitudes (visual magnitudes for the Sun and full Moon are -26.8 and -12.5 respectively). On a clear night, the dimmest stars will have magnitudes around +6.

Previous confrontation

What can you say about the dates of the opposition of the planets? You may have heard that Mars reached opposition on July 27, 2018. But what does that mean? That Mars is bright and easy to spot in the night sky. It's called opposition because that's when it's 180 degrees away from the Sun, which is right next to it. As the sun sets, Mars rises and crosses the sky throughout the night, disappearing at dawn.

Moon in the morning

Opposition also occurs when the distance from the planet to the Earth reaches a relative minimum, because it is closer, it appears larger and brighter in our sky. Already since the spring we have seen the opposition of Jupiter (May 9) and then Saturn (June 27), so it was a good summer for viewers of the planet. (Uranus, Neptune, and Pluto also reached opposition this year, but they are all so dim that most casual stargazers won't see them at all.)

What planets can be in opposition? This has already been said before, but much depends on the orbit. They set opposition in motion, and Mars's oppositions are a bit more complex than others because its orbit is much more elliptical than planets like Jupiter and Saturn.

As astronomer Johannes Kepler described in the early 1600s, the planets follow elongated circles - ellipses, rather than perfectly circular paths around the Sun. This is the answer to the question which planets interact with each other in opposition.

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