Observation Mars Oppositions

Mars' opposition, like for any superior planet -those planets located beyond the Earth relative to Sun- occurs when the Red planet lies in line with the Sun and the Earth due to its orbit related to Earth's. Due to the relative proximity of Mars' orbit to us however, a Martian opposition occurs every 26 months only compared to one year for other superior planets. When that time occurs, Mars is seen at its best observable in terms of apparent diameter and magnitude. Mars is rising by sunset and setting by sunrise. for more about the remarkable positions of the planets, see our tutorial Planets Apparent Motion. The geometry of both Mars and Earth's orbits makes that Mars closest approach to Earth occurs close (before or after) the opposition, by some days (or more), mostly yielding a slightly smaller (before) or slightly larger (after) apparent diameter. The concept of a 'Mars Observation Campaign,' further refers to that afficionados are deeming Mars worth observing from when it is reaching 6 arcminutes of apparent diameter to when it reaches back that value, or about more or less 12 months. Modern CCD cameras might pushed back that limit down to 4.3 arcminutes. Mars opposition are too a good opportunity for non-afficionados to get into the discovery of the Red Planet, as they can take advantage of Mars largest apparent diameter

A view of how the apparent diameter of Mars is varying along a Mars Observation Campaign! site 'Amateur Astronomy'

Another more specialized concept used, is the one of a 'cycle of Martian apparitions.' Such a cycle is lasting about some 15 years, which represents a length of years necessary to observe the whole of Martian seasons during the times of a opposition. A cycle of Martian apparitions is beginning with the first Mars' apparition which occurs after the vernal equinox in Mars' northern hemisphere, which is about Earth's December or January. A cycle is ending about 15 years later, by November. As the last cycle extended 1993-2005, we currently are inside the 2007-2022 one. Such considerations, for example, are determining whether Mars will endure dust storms or not, or whether the opposition will allow to a transition between two Martian seasons. Along a cycle of Martian apparitions, at last, the apparent diameter of the Red Planet may vary strongly from a opposition to a other. On that 15-year cycle, on a other hand, three or four aphelic oppositions (with Mars at its farthest Sun) and three consecutive perihelic oppositions (Mars at its closest Sun) occur. A 'transitional' opposition defines a one between aphelic and perihelic

A view of how a dust storm may affect the view of Mars at opposition. Mars at opposition with usual conditions (left, May 12, 2016) and a dust storm (right, July 18, 2018); North pole is more inclined towards the observer in the first picture based upon picture NASA, ESA, and STScI

When considering a Martian campaign, it is of use too to get informed about how high Mars will be lying in the sky at the time of the opposition. According to each opposition that altitude may vary a lot. The more Mars high above the horizon the more favourable the observation! A Moon present in the sky -and the phase of it- may also be a factor. additional considerations about observing Mars are also available with our Planetary Basics tutorial (when you will be able to accede to that advanced page: Additional Factors To Planets' Visibility)

Varied Values About Recent Mars' Oppositions

Opposition's Approximate Date	Mars Apparent Diameter (in ")	Remarks	Altitude Above the Horizon (North. Hem.)	Altitude Above the Horizon (Tropics)	Altitude Above the Horizon (South. Hem.)
early Mar. 2012	13.9	-	60	78	49
early Apr. 2014	15.0	-	45	84	65
late May. 2016	18.3	-	29	68	81
late Jul. 2018	24.2	officially a perihelic	25	64	84
late Oct. 2020	22.4	-	56	84	54
early Dec. 2022	17.0	-	75	65	35
mid Jan. 2025	14.5	-	76	64	34

->What Perihelic Oppositions Are
The combined characteristics of the Earth and Mars' orbits with, among others, that orbits in the solar system are ellipses featuring a closest (or perihelion) and a farthest (or aphelion) from the Sun, make that the distance between the Earth and Mars at a opposition is varying between 34.8 and 62.8 miles at the perihelion and aphelion respectively. That translates into a apparent diameter varying from 14 (when the opposition occurs at Mars' aphelion) to 25.5 degree (when at Mars's perihelion). Oppositions occurring at Mars' perihelion are best observed from the southern hemisphere because higher in the sky. Every 15-17 years, when Mars reaches a perihelion, that yields a perihelic opposition -which can be increased due to that Earth may reach a aphelion. The minimal distance between Mars and the Earth is governed by a cycle of 15, 32, 47 and 79 years. The minimum of 187 million miles is seen every 47 ans (the closest now will be by August 2018). Dates of a perihelic opposition of Mars during the 21st century are: 2003, 2018, 2020, 2035, 2050, 2065, 2067, 2082, and 2097. The next best perihelic opposition, like the one of 2003 (at 25.13" of apparent diameter) will be seen by 2729 only, as both last best had occurred by 1945 and 1924. Such closest are due to the respective change in the orbit's eccentricity of both Mars and the Earth which are to turn more and more favourable along with the next millenia

For information, articles about Martian opposition are often quoting -or showing a diagram with- the 'Ls' value at Mars. That value defines where the Sun stands on the ecliptic as seen from Mars relative to Mars celestial equator. 0° Ls has the northern hemisphere vernal equinox occurring, when the Sun crosses Mars' celestial equator from South to North. Mars summer solstice is at 90° Ls, the autumnal equinox at 180° Ls as the winter solstice is at 270° Ls. Seasons are the opposite for Mars' southern hemisphere