Mars at Perigee

This Week, Mars Will Make Its Closest Approach To The Earth In Years To Come: 3 Things To Know

The second half of 2020 is all about the grand show of Mars. It all started on August 9 when the Moon eclipsed the planet – a lunar occultation. There were 3 lunar occultations in a row – August 9, September 6, and October 3. Though the occultations were visible from a small part of the world, the proximity of the two celestial bodies was a treat to watch on the given dates.

Watch all the astronomy events in October 2020

But that was not the only reason to look up for the Red Planet. Mars has been coming closer and closer to our planet – increasing in brightness every week. A few months ago, Mars was nothing but a faint uninteresting speck of light in the night sky. But now, it has outshone Jupiter and Sirius (the brightest star in the night sky) and has become the third brightest object in the night sky, only after the Moon and Venus. Venus rises a couple of hours before dawn so the night sky is essentially dominated by Mars.

The reason behind the increase in the brightness is that Mars is approaching its opposition in October. So here are three things to know about this flagship astronomical event of this month.

1. 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. 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.

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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%.

Credits: Dominic Ford, in-the-sky

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.

Around the same time, a planet also reaches its perigee (a point in the planet’s orbit that is closest to the Earth). This year, Mars will be at perigee on October 6 and at opposition on October 14. This huge gap between the two dates is because of the elliptical orbit of Mars.

2. How Close Will Be Mars?

As stated above, the fall opposition is special as it brings Mars closer to the Earth than the spring opposition. On October 6, Mars will be at a distance of 0.42 AU, i.e., 73.3 million Km away from the Earth. This is less than half the distance between the Earth and the Sun.

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3. How To Observe Mars

Sky chart for October 6 (Image: Dominic Ford, in-the-sky)

Mars is well up in the sky a few hours before midnight. It rises in the East (in Pisces) around 19:00 and sets in the West at 07:20. Hence, it is visible all night. The apparent magnitude of Mars is -2.60 making its the brightest speck of light in the sky after the Moon and Venus.

Mars at perigee 2020

This is the best time to capture Mars in a camera using a telescope. Its angular diameter has increased significantly. The above image was captured by astrophotographer Nikunj Rawal from Gujarat, India. You can clearly see the polar ice caps. This was captured using a DSLR through 4X Barlow from 8″ Sky-Watcher Dobsonian telescope.

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