On 13th October, Mars and the Sun lined up with Earth in the middle called Mars Opposition.
What is an Opposition in Astronomy?
- At opposition – Earth is in the middle of a line between an outer planet and the Sun, we see the sun at one end of our sky and the opposition planet in the opposite direction.
- When the Sun sets in the west, the planet is rising in the east. As the planet drops below the horizon, the Sun pops above it again: opposite.
- Opposition for an outer planet happens when the Sun and that planet are exactly 180 degrees apart in the sky.
Planets that can be at Opposition
- Oppositions can only happen for objects that are farther from the Sun than Earth is. We can see oppositions for Jupiter, Saturn, Uranus and Neptune about every year. They happen as Earth, in its much-faster orbit, passes between these outer worlds and the Sun.
- We see oppositions of the planet Mars, too, but Martian oppositions happen about every 27 months because Earth and Mars are so relatively close together in orbit around the Sun; their orbits, and speeds in orbit, are more similar.
Planets that cannot be at Opposition
- Venus and Mercury can never be at opposition as seen from Earth. Their orbits are closer to the Sun than Earth’s, so they can never appear opposite the Sun in our sky. These inner planets always stay near the Sun, no more than 47 degrees from the Sun for Venus, or 28 degrees for Mercury, in our sky.
Why Mars Opposition Occurs only every Two Years?
- Mars orbits the Sun once every 687 days, so roughly 2 years. We on Earth travel a much higher speed and only require 365 days to orbit.The Earth would lap Mars at some point during its orbit. Given that Mars is also orbiting, one trip around the Sun would not suffice, however. Only after 780 days will the Earth and Mars be aligned once again. An opposition!