It is believed that in positional astronomy two objects are in opposition (opposition) when they are located on opposite sides of the celestial sphere, as is observed from a third (side) celestial body (usually from the Earth).
It is said that a planet (or an asteroid / comet) is “in opposition” when it is on the opposite side of the Sun. Since most of the orbits of the solar system are almost coplanar to the ecliptic, this happens when our sun, the Earth and the third celestial body are configured on approximately the same straight line or syzygy. The earth and this third celestial body are in the same direction as the sun. Confrontation occurs only on higher planets.
Details
When viewed from a superior planet, the lower one on the opposite side of the Sun is in excellent conjunction with it. A low connection occurs when two planets coincide on one side of the sun. Under him, the higher planet “resists” the luminary, as viewed from its side.
Mars role
Like all 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.
Therefore, sometimes two planets are located on opposite sides of the Sun, very far from each other, and in other cases the Earth catches up with its neighbor and passes relatively close to it.
Planets Confrontation: Earth and Mars
During the confrontation, Mars and the Sun are directly on opposite sides of the Earth. In our view 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 goes west just as our luminary rises in the east.
As Mars and the Sun appear on opposite sides of the sky, we say that the Red Planet is in “opposition”. If the Earth and Mars followed in completely circular orbits, the confrontation would be as close as two planets could reach.
Periodicity
Planetary confrontation, in the case of Mars, occurs approximately every 26 months. The confrontation occurs within a few weeks after perihelion (points in its orbit when the planet is closest to the Sun).
Last year, the confrontation 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 (the so-called "perihelion opposition"), it is especially close to the Earth. If the latter and Mars had absolutely stable orbits, then each perihelion confrontation would bring the two planets closer together as close as possible. It is almost like that.
But then again, nature adds a few complications. The gravitational attraction of other planets constantly changes the shape of our orbits. The 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
The orbit of Mars is more elliptical than the Earth, 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 luminary in perihelion and even further in aphelion. Thus, future perihelion confrontations of the planets will bring Earth and Mars closer together.
Earth and other planets in the solar system do not own a specific 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 if there is a relative elongation of the Sun (measuring the angle between the planet and the luminary) equal to 180 °, which is considered the maximum elongation. Simply put, the confrontation of planets is when the celestial body is opposite the Sun in the sky of the Earth or when the latter is located between it and the luminary.
The reference point is always the sun. Higher planets, whose orbits are located outside the Earth, may be in opposition to it. A great time to view the planet is solar lengthening. On the other hand, lower planets, such as Mercury and Venus, have elongation periods different from the higher ones, which are further from the Sun than from the Earth.
Other characteristics
When a superior object, the Earth and the Sun align in a straight line with our planet between them, this is called opposition. When the higher planet and the Earth lie on opposite sides of the Sun, this is called conjunction. It is noted that the confrontation of some planets makes them closer to the Earth, and this will be an appropriate time to observe the higher planet.
Jupiter
What planets can be observed in opposition, besides 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 in accordance with the position of Jupiter in the celestial sphere and corresponded to 12 earth branches (a cycle of 12 animals). So he is also known as the Star of the Century. The opposition of Jupiter will occur approximately once every 399 days.
Jupiter is the second brightest planet after Venus. A few weeks before and after the confrontation, Jupiter is very bright, reaching a visual value of about -2.5 *. This will be a good time to observe him, his Great Red Spot and the four largest satellites, namely Io, Europe, Ganymede and Callisto. A telescope with a magnification of 40 times or more is preferred when observing Jupiter.
Visual magnitude
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 magnitude. The brightest celestial objects will have negative values (visual values for the Sun and the full Moon are -26.8 and -12.5, respectively). On a clear night, the faintest stars will have a magnitude of about +6.
Previous confrontation
What about the dates of the confrontation of the planets? You may have heard that Mars reached the opposition on July 27, 2018. But what does it mean? The fact that Mars is bright and easy to see in the night sky. This is called the opposition, because it is then that it is 180 degrees from the Sun, which is located in close proximity to it. When the sun sets, Mars rises and crosses the sky all night, disappearing at dawn.
The confrontation also occurs when the distance from the planet to the Earth reaches a relative minimum, because it is closer, it seems bigger and brighter in our sky. Already in the spring we saw the confrontation of Jupiter (May 9), and then Saturn (June 27), so it was a good summer for the audience of the planet. (Uranus, Neptune and Pluto also reached opposition this year, but they are all so vague that most random stellar observers will not see them at all.)
What planets can be in opposition? This has already been said before, but much depends on the orbit. They set the opposition in motion, and the counteractions of Mars are a little more complicated than others, because its orbit is much more elliptical than that of such planets as Jupiter and Saturn.
As astronomer Johannes Kepler described in the early 1600s, planets follow elongated circles - ellipses, and not perfectly circular paths around the Sun. This is the answer to the question of which planets in the confrontation interact with each other.