Since the first lunar occultation of Mars in August, the Red Planet has been in news. It disappeared behind the Moon on August 9 and then on September 6. Although these events were visible from only a few parts of the world, the proximity of the Moon and Mars was a treat to watch for every sky gazer.
With each passing day, the show is getting better and better. Mars is approaching its opposition and perigee. As of September 12, 2020, it has already outshone Sirius, the brightest star in the night sky. In the next couple of weeks, Mars will become brighter than Jupiter. It will become the brightest planet in the sky, only after Venus. This article explains how to spot Mars and why the upcoming opposition is so special. But first, let us get familiar with the concept of magnitude in astronomy – a number that tells how bright an object is.
Magnitude And Brightness In Astronomy
Generally, the magnitude of a quantity refers to the numeric value of something. For example, consider velocity v = 40 km/hr due East. This vector quantity has a magnitude and a direction. The magnitude of velocity is 40 while the direction is East. But the concept of magnitude in astrophysics has nothing to do with vectors like stated above. In Astrophysics, magnitude is a measure of the amount of energy emitted by a body over the entire EM spectrum. Roughly speaking, it is the measure of the “brightness” of an object.
There are three types of magnitudes in Astronomy but here we are only interested in one: the Apparent magnitude. It is a number that describes the brightness of an object. The most important thing to be noted is: higher the number, fainter the object as shown below:
The apparent magnitude of the Sun is -26.74 and that of the brightest star in the night sky is -1.74. With our naked eye, we can see up to a magnitude of +6.0. You can read this article of our Basics of Astrophysics series to learn about the concept of magnitude in detail.
The Brightness of Mars
The apparent magnitude of Mars as of September 12, 2020, is -2.05 which means it has outshone Sirius. Soon, it will become brighter than Jupiter that is currently at a magnitude of -2.5. Jupiter and Saturn made their closest approach to the Earth in July so they are fading now.
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October 14: The Day of Special 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.
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.
How To Watch Mars In The Night Sky?
Mars rises in the East around a couple of hours after sunset and is high up in the sky after midnight. It is then lost to dawn twilight. Currently, Mars is in the constellation of Pisces shining at mag -2.08 and its altitude and brightness will increase as days go by. Currently, Mars is at a distance of 0.46 AU from the Earth. It’s getting closer and closer. On October 6, Mars will make its closest approach to the Earth and appear bigger than normal (in a telescope). The opposition is a week later.
A Treat On October 3
On October 3, the Moon will occult Mars for the last time in 2020.
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.
On this occasion, the occultation will be visible from the parts of South America. For the rest of the world, the two celestial bodies will appear to pass close to each other.
Enjoy the grand show of the Red Planet in the next few weeks! Share this with your social circle.