Solar System Phenomena — Mars in 2018

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The upper chart shows the path of Mars across the background stars over the course of the year. Stars to magnitude +4.5 are shown with some fainter objects included to complete constellation patterns. The white circles represent the planet on the first day of the month and are scaled according to apparent magnitude. The faint paths before the first circle and after the last circle represent the planet's positions in December of last year and January of next. In general, the planet moves from right to left except when it's in retrograde and proceding in the opposite direction.

The lower chart shows how the appearance of Mars changes over the year. Below each image is listed the date, the apparent magnitude, the apparent diameter of the disk (in arc-seconds), the geocentric distance (in au) and the percentage of the disk which is illuminated. Note that Mars appears distinctly gibbous near the times of quadrature.

The red planet begins the year in the morning sky, sharing the constellation Libra with its giant neighbour Jupiter with which it has a close encounter early in January. Rising ever farther ahead of the Sun, Mars next encounters a planet in April when it passes near Saturn. Opposition occurs at the end of July. This is a particularly favourable opposition from an observational standpoint with the disk of Mars appearing over 24 arc-seconds in diameter. The planet is easiest to see from southern latitudes this year although northern observers finally get some better views toward the end of 2018 when Mars is an evening sky object.

07 January0.2° south of Jupiter
30 JanuaryLibraScorpius
07 FebruaryScorpiusOphiuchus
11 MarchOphiuchusSagittarius
16 Marchdescending node
20 March0.8° north of NGC 6530, an open star cluster within M8, the Lagoon Nebula
24 Marchwest quadrature
02 Aprilplanetary conjunction: 1.3° south of Saturn
14 MaySagittariusCapricornus
22 Mayequinox: autumn in the northern hemisphere and spring in the southern hemisphere
28 Junestationary point: direct → retrograde
27 Julyopposition: magnitude −2.7, apparent diameter 24.2 arc-seconds
31 Julyminimum distance from Earth: 0.385 au
16 Augustmaximum declination south
28 Auguststationary point: retrograde → direct
16 Septemberperihelion
16 Octobersolstice: winter in the northern hemisphere and summer in the southern hemisphere
18 October1.9° south of the Moon
10 NovemberCapricornusAquarius
16 Novemberlunar occultation: 1.0° north of the Moon
03 Decembereast quadrature
07 Decemberplanetary conjunction: 0.4° north of Neptune
21 DecemberAquariusPisces
31 Decembermaximum declination north


The dates, times and circumstances of all planetary and lunar phenomena were calculated from the JPL DE406 solar system ephemeris using the same rigorous methods that are employed in the compilation of publications such as The Astronomical Almanac.