Mars in opposition

Red hot Our planetary neighbour Mars will appear its brightest today, giving us a rare insight into a phenomenon called the ‘Mars opposition’. Watch this celestial event enliven the night sky, writes S A Mohan Krishna.

Have you seen Mars in the evening sky? 

If not, you are missing out on something really magical.

Mars is the fourth planet from the Sun.

It moves in a conspicuously elliptical orbit, its mean distance from the Sun being 1.52 times that of the Earth’s. 

Mars will be sprinting adjacent enough to Earth to be discernible with the naked eye at the end of this month. 

On April 8, 2014, the two planets  will be close to each other, maintaining a distance of about 9 crore 23 lakh km or 0.61 AU. 

Mars will look like a resplendent red star in the sky.

Planet sighting

Presently, Mars can be seen in the Virgo constellation at around 10 pm with the naked eyes and is in line with Jupiter. 

On August 27, 2003, the orbits of Earth and Mars brought the latter planet to as close as 34.6 million km.

The average distance between the two planets is about 225 million km, so this was a unique opportunity to observe Mars.

The last time it was this close to the Earth was in the year 57,537 B C. The next time Mars will be as close to the Earth as it was in 2003 will be on August 28, 2287. 

The changing distance between Mars and Earth at oppositions is mainly due to the oval-shaped path of Mars around the Sun. 

When Mars and the Sun are seen in opposite directions in the sky, this is called ‘opposition’ and if Mars is very close to Sun and far away from the Earth, it is then referred to as ‘conjunction’. 

Mars oppositions occur when planet Earth, on its inner orbit, passes between the Sun and Mars.

The spectacular Mars opposition of August 2003, when the red planet was only 56 million km from Earth, took place when Mars was near perihelion, its closest distance to the Sun. Conversely, at the current opposition, the distance of Mars from Earth will be 9 crore 23 lakh km, almost twice the distance in 2003, as Mars is near its aphelion, its farthest distance from the Sun.

The favourable oppositions of Mars take place in a cycle of around 17 years. 

The last favourable one was in 2003 and the next one will be in October 2020. 

The best known favourable opposition of Mars was in September 1877. 

It allowed American astronomer Asaph Hall to discover the two tiny satellites circling Mars using the large 26-inch-lens telescope at the US Naval Observatory in Washington DC. He named the two moons phobos meaning fear and deimos meaning flight. 

Another observer in 1877, was the Italian astronomer Giovanni Virginio Schiaparelli who made careful observations of the planet during the opposition in order to draw a new map of its surface features.

 On his map, he included some linear features that he called canali, which in Italian  means natural features.

However, the word was translated as canals in English, and so began a whole culture of belief in intelligent beings on Mars or Martians.

Matter of distance 

In general, the closer Mars is to perihelion at opposition, the closer it is to the Earth, and the closer it is to aphelion at opposition, the further it is from the Earth. 

But although opposition and closest approach are close together at perihelion (as in 2003) and aphelion (as in 2014), if Mars is moving away from the Sun (between perihelion and aphelion), closest approach is several days earlier than opposition. 

Similarly, if Mars is moving toward the Sun (between aphelion and perihelion), closest approach is several days later than opposition. 

As a result, the distance at closest approach can be somewhat different than might be expected, based only on Mars’ position at opposition.

Mars rises in the east around sunset, climbs highest around midnight and sets in the west around sunrise. 

This brilliant world now shines from dusk till dawn. It’ll be hard to miss because it’s the fourth-brightest star-like object to light up the night at this time, after the planets Venus, Jupiter, and the star Sirius.

Because of the orbits of the two planets, opposition occurs about every two years and two months. 

After that period of time, the Earth revolves around the Sun exactly one time more than Mars. 

The orbit of planet Mars is subject to small and slow secular changes caused by various perturbations, in particular, the gravitational perturbations by the other planets. 

One of these effects is that the eccentricity varies over the millennia, and thus the perihelion and aphelion distances of Mars are subject to minor changes.

The Earth has started to overtake Mars, giving us a biannual opportunity to view the red planet from a relatively close vantage point. 

At present, Mars rises at around 9:00 pm and is now very prominent after midnight in the eastern sky. 

Mars will have an angular diameter of 13 arc seconds with a visual magnitude — 1.23 and little more than 2 percent of the diameter of the full moon.

Use of telescope

Moderately powerful telescopes or binoculars are required to focus the disc of the Moon. 

A magnification of about 90X will make Mars look as big as the full moon as seen without a telescope. 

Through a good telescope, the planet will appear as a small orange disc with dark markings.

Usually the telescope will also show a white polar ice cap and occasionally clouds in the very thin Martian atmosphere. 

More rarely, the surface markings can be completely obscured by dust storms that can envelop the planet for weeks.

When viewed from the Earth, Mars is on the opposite side of the sky from the Sun.

Opposition is the time in each 26-month cycle when Mars and Earth are closer together.

Earth can be closer or further from Mars at opposition, depending on where in the orbit is Mars, when Earth passes it. 

The Red Planet is about to be spectacular! 

This month and next, Earth is catching up with Mars in an encounter that will culminate in the closest approach between the two planets in recorded history. 

The next opposition of Mars is in 2015. Do not forget to see Mars today and enjoy the grandeur of astronomy.