International Space Agencies – Missions and Discoveries

Mars ‘Opposition’ Event

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Opposition event

Mains level : Not Much

Due to an event referred to as “opposition”, which takes place every two years and two months, Mars will shine the brightest.

Try this question from CSP 2017:

Q.Which region of Mars has a densely packed river deposit indicating this planet had water 3.5 billion years ago?

(a) Aeolis Dorsa (b) Tharsis (c) Olympus Mons (d) Hellas

What is the Opposition Event?

  • ‘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.
  • It 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.

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, the opposition can happen only for planets that are farther away from the sun than the Earth.
  • In the 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.
  • Further, 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, however, 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.

Logic behind the name

  • 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, the opposition is a reference to “opposing the sun” in the sky.
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