Three Kinds of Opposition. Astronomy enthusiasts generally define opposition as the time a planet is opposite the sun. This is correct. Except that the word opposite is not technically well-defined. In fact, planets are never really opposite the sun because their orbits are not coplanar with Earths. So as we celebrate the various oppositions of Mars, let us take the time to understand the differences between them. 1. Opposition in Right Ascension - this is the exact moment when the right ascension of the planet is 180 degrees from the right ascension of the sun. In the Philippines, the Opposition of Mars in Right Ascension occurred on 2014 April 9 at 10:37:10 PM. 2. Opposition in Ecliptic Longitude - this is the exact moment when the ecliptic longitude of the planet is 180 degrees from the ecliptic longitude of the sun. In the Philippines, the Opposition of Mars in Ecliptic Longitude occurred on 2014 April 9 at 5:03:13 AM. The US Naval Observatory uses this in its astronomical calendar, so this is the time usually quoted. 3. Maximum Elongation - this is the exact moment when the angle between the planet and the sun reaches its maximum value before it becomes smaller again. In the Philippines, the Maximum Elongation of Mars occurred on 2014 April 9 at 6:00:42 AM. This is already daytime. In general photographers who want the largest theoretical disc should aim for this kind of configuration than the previous two. For those interested, the book Astronomical Algorithms by Jean Meeus provides a great way to learn to compute these planetary configurations. Ad astra per aspera.
Posted on: Wed, 09 Apr 2014 16:35:49 +0000
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