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Explained: Why Mars is the brightest this month thanks to Opposition

14th October, 2020 Science and Technology

Context: Due to an event referred to as “opposition”, which takes place every two years and two months, Mars will outshine Jupiter, becoming the third brightest object (moon and Venus are first and second, respectively) in the night sky during the month of October.

So what is opposition?

  • Opposition is the event when the sun, Earth and an outer planet (Mars in this case) are lined up, with the Earth in the middle.
  • The time of opposition is the point when the outer planet is typically also at its closest distance to the Earth for a given year, and because it is close, the planet appears brighter in the sky.
  • An opposition can occur anywhere along Mars’ orbit, but when it happens when the planet is also closest to the sun, it is also particularly close to the Earth.

When does opposition happen?

  • Earth and Mars orbit the sun at different distances (Mars is farther apart from the sun than Earth and therefore takes longer to complete one lap around the sun).
  • In fact, opposition can happen only for planets that are farther away from the sun than the Earth.
  • In case of Mars, roughly every two years, the Earth passes between sun and Mars, this is when the three are arranged in a straight line.
  • As the Earth and Mars orbit the sun, there comes a point when they are on the opposite sides of it, and hence very far apart. At its farthest, Mars is about 400 million km from the Earth.
  • In case of opposition, Mars and sun are on directly opposite sides of the Earth. In other words, the Earth, sun and Mars all lie in a straight line, with the Earth in the middle.
  • As per NASA, Mars made its closest approach to Earth in 2003 in nearly 60,000 years and it won’t be that close to the planet until 2287.
  • This is because the orbits of Earth and Mars are not perfectly circular and their shapes can change slightly because of gravitational tugging by other planets. For instance, Jupiter influences the orbit of Mars

But why is it called opposition?

  • As per NASA, from an individual’s perspective on the Earth, Mars rises in the east and after staying up all night, it sets in the west just as the sun rises in the east and sets in the west.
  • Because from the perspective on Earth, the sun and Mars appear to be on the opposite sides of the sky, Mars is said to be in “opposition”.
  • Essentially, opposition is a reference to “opposing the sun” in the sky.

And how can one view Mars?

  • Opposition is the best time to view Mars.
  • During this time, Mars will appear as a bright star to the unaided eye and when viewed from a telescope, “it will grow dramatically in size”.
  • Using a telescope shows more of the planet’s details such as dark and light regions, the solar ice caps and Mars’ surface.
  • But the clarity of these details depends on the turbulence of the atmosphere and local weather conditions.