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Our neighbouring planet Mars at one time in history could have been mistaken as a twin of the Earth, with high temperatures and oceans of water on the surface. Now, it is cold and dry with little evidence of water. This month Mars will reach opposition: an event that only happens once every two years.

Kenzie Nimmo

Hey! I’d like to take this opportunity to introduce myself. I’m Kenzie Nimmo, a PhD researcher working at the Anton Pannekoek Institute (API). This academic year I’ll be writing monthly blogs on various topics, from research that we conduct here at API to blogs related to upcoming astronomy events.

This month we have a very exciting event coming up. On October 14th 2020, our neighbouring planet Mars will reach opposition. We are celebrating by hosting a Mars event which will be livestreamed on YouTube. For more information on this event, please see the agenda item below.

What is an opposition? Opposition is a specific alignment of the Sun, the Earth and a planet, in this case, Mars. It represents the point where the Earth intersects the line connecting the Sun and Mars. During opposition, the red planet will be one of the brightest objects in the sky. Because Mars takes twice as long as Earth to orbit the Sun, a Mars opposition only occurs once every two years.

Diagram depicting Mars opposition. The aphelion is the point in an orbit where the object is farthest from the Sun, and the closest point is the perihelion. The Mars opposition in October 2020 is after the perihelion point of the orbit, but closer to the perihelic opposition than the aphelic, meaning it will be the brightest opposition of Mars for another approximately 10 years

Because by definition, at opposition, the planet is directly opposite the sun, it will be visible throughout the night, rising in the East around sunset and setting in the West around sunrise.. If the sky is clear, you will be able to see Mars with the naked eye. To distinguish Mars from other planets and stars, first make sure it is not twinkling. Stars twinkle due to an effect called scintillation, but planets do not visibly twinkle. The second check is to make sure Mars has a reddish tint (Mars does have the nickname “the Red Planet”, after all).


The path Mars makes across the sky at night close to opposition. (Stellarium)

Finally, why is Mars interesting? Mars is the most similar planet to Earth in our Solar System. Mars sharing similar properties to Earth implies that perhaps Mars could also host life, or has done in the past. Studies suggest that Mars was once warmer, contained more water, and had a thicker atmosphere, making it more habitable. Mars is clearly a very exciting object to study, and at ‘only’ 65 million kilometers away, it’s a perfect target for exploration. NASA recently launched the Perseverance rover in July 2020, which will reach Mars in February 2021, to answer questions regarding the potential for life on Mars.