After being ‘eclipsed’ by the Moon in the first week of August, Mars is in news again. The Red Planet is gearing up for its best show in the night sky in the years to come. Currently, Mars has an apparent magnitude of -1.6, which means it is almost as bright as Sirius – the brightest star in the night sky.
But, over the course of September and October, Mars will become the brightest planet in the night sky after Venus. This is because Mars is approaching its opposition – its closest approach to the Earth – on October 13. In fact, by the time you read this line, Mars will be 40 km closer than before!
Let us why this opposition is special and how we can observe the planet in the night sky?
What Is An Opposition?
In celestial mechanics, a planetary opposition occurs when the Earth lies between the Sun and the planet with Earth being on the same side of the planet as shown below.
During opposition, the planet lies opposite to the Sun. Hence, it rises around the sunset, reaches the highest point in the sky around midnight, and sets at dawn. This is the best time to observe a planet. Jupiter and Saturn were at opposition on July 14 and July 21 respectively. You can read this article to know how to watch them together.
Why Is This Opposition Special?
As the two planets pass each other, Mars makes its closest approach to the Earth and appears larger and brighter than at other times. Lying opposite to the Sun in the sky, it also appears high in the sky for much of the night.
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Every superior planet makes its closest approach to Earth once a year i.e. each of them is at opposition on a particular date. The oppositions of Jupiter, Saturn, Uranus, and Neptune are more or less the same each year. But this is not the case for Mars, which has a highly elliptical orbit.
Due to an elliptical orbit, a planet reaches its perihelion and aphelion. Although the distance from the Sun varies by just 3% for the Earth, in the case of Mars, owing to the high eccentricity, the distance varies by 20%.
You can see from the above image how eccentric the Martian orbit is as compared to the Earth. During an aphelion opposition that takes place around March, the distance between the two planets is still 0.66 AU. But, during the August-September opposition, also known as the perihelion opposition, Mars can come within 0.41 AU of the Earth, appearing 60% larger than at a March opposition, and a whole magnitude brighter.
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How To Watch Mars In The Night Sky?
Mars rises in the East around a couple of hours before midnight and is high up in the sky around 04:00. It is then lost to dawn twilight. Currently, Mars is in the constellation of Pisces shining at mag -1.64 and its altitude and brightness will increase as days go by. Currently, Mars is at a distance of 0.52 AU from the Earth. It’s getting closer and closer. On October 13, around opposition, Mars will make its closest approach to Earth and appear bigger than normal (in a telescope).
The Lunar Occultation of Mars
On September 6 and October 3, the Moon will occult Mars. The term occultation is mostly used when the Moon passes in front of an astronomical object. The Moon’s orbit is inclined slightly with respect to the ecliptic meaning any stars with an ecliptic latitude of less than about ± 6.5 degrees may be occulted by it. Since the planets also lie in the ecliptic, they are often occulted by the Moon.
Lunar occultations are only ever visible from a small fraction of the Earth’s surface. Since the Moon is much closer to the Earth than other celestial objects, its exact position in the sky differs depending on your exact location on Earth due to its large parallax. The position of the Moon as seen from two points on opposite sides of the Earth varies by up to two degrees or four times the diameter of the full moon.
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This means that if the Moon is aligned to pass in front of a particular object for an observer on one side of the Earth, it will appear up to two degrees away from that object on the other side of the Earth.
The Lunar Occultations will be visible from the parts of South America and Africa. For the rest of the world, the Moon and Mars will appear very close to each other.
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