The Mars Apparition of 2015-2017

by Martin J. Powell

At superior conjunction on June 14th 2015 (when it passed directly behind the Sun in the constellation of Taurus), the planet Mars was positioned 2.5675 Astronomical Units (AU) from Earth (384.1 million kms or 238.6 million miles). Had it been visible from Earth at this time, it would have had an apparent magnitude of +1.5 and an apparent size of only 3".6 (i.e. 3.6 arcseconds, where 1" = 1/60th of an arcminute or 1/3600 of a degree). Mars entered the constellation of Gemini, the Twins, on June 25th. On July 11th the Red Planet reached its most distant point from the Earth (sometimes referred to as the apoareion) for this apparition, a distance of 2.5869 AU (386.9 million kms or 240.4 million miles). The planet now shone at an apparent magnitude of +1.6 and had an apparent diameter of 3".6. Mars entered Cancer, the Crab, on August 5th, at which time it was positioned 15° West of the Sun.

The Red Planet's 2015-17 apparition truly began as it emerged into view from the bright dawn twilight around late July, when it was seen rising in the Eastern sky from Northern Tropical latitudes. In early August Mars was rising in twilight across the inhabited world, pulling away from the Sun at a rate of just 0°.3 per day. The planet was visible for a period of time which was dependant upon the observer's latitude and the local season. Mars rose 1½ hours ahead of the Sun at latitude 50° North, 1¼ hours before the Sun at 40° North, 1 hour before sunrise at the Equator and only 45 minutes before sunrise at latitude 35° South.

Around mid-August Mars was moving steadily Eastward against the background stars at a rate of about 0°.6 per day. From mid-Southern latitudes Mars began to appear in the dawn sky around this time, when Mars was passing through the star cluster known as Praesepe (pronounced 'PRE-SEEP-EE'), designated Messier 44 (M44 or NGC 2632). It is also known by the names Beehive Cluster or The Manger. Mars passed through Praesepe over a 40-hour period from 18 hours UT on August 19th to 10 hours UT on August 21st. However, being just 20° from the Sun, only observers at Northern Tropical latitudes were able to view it (a few degrees above the ENE horizon), and even then for a short period of time.

At this early stage in the apparition, Mars appeared as a feeble, pale-orange star, shining about as bright as the star Castor ( Gem or Alpha Geminorum, mag. +1.6), the second-brightest star in Gemini. Mars barely gained any significant altitude (angle above the horizon) before disappearing into the brightening dawn twilight. Telescopically the planet was a disappointing sight, its low altitude and tiny apparent size (ca. 3".7) frustrating most attempts to obtain a steady and clear view of the planet's surface.

On August 22nd Mars passed between the two Ascelli in central Cancer - namely, the stars Asellus Borealis ( Cnc or Gamma Cancri, mag. +4.6) and Asellus Australis ( Cnc or Delta Cancri, mag. +3.9). The planet passed 1°.1 North of Asellus Australis and 2°.2 South of Asellus Borealis, i.e. at about one-third of the distance between them. On August 27th the planet passed 6°.4 North of the star Acubens ( Cnc or Alpha Cancri, mag. +4.2) at the South-eastern corner of the constellation's lambda-shaped () pattern.

In late August Mars experienced the first of six planetary conjunctions which took place during the planet's 2015-17 apparition. A planetary conjunction takes place whenever any two planets attain the same celestial longitude in the night sky. Venus, shining at magnitude -4.2, was entering the morning sky at the start of its 2015-16 apparition as a 'Morning Star', becoming visible at dawn from around August 20th. Venus was slowly retrograding (moving East to West) in the South-eastern corner of Cancer whilst Mars was moving more speedily in the opposite direction several degrees to the North. The two planets crossed the same longitude (Right Ascension = 9 hours 3 minutes) on August 29th, Venus being a sizeable 9°.4 to the South of the Red Planet. Mars had faded slightly to magnitude +1.7 and the pair were positioned some 22° West of the Sun at this time.

Mars left Cancer and headed into Leo, the Lion, on September 5th, passing 5°.2 North of the star Subra ( Leo or Omicron Leonis, mag. +3.5) at the tip of the Lion's foreleg, on September 13th. Between September 15th and 29th Mars was positioned South of the asterism known as the Sickle of Leo, at the Western end of the constellation, which appears to the naked-eye as a backward question-mark (). Using this analogy, Leo's brightest star Regulus ( Leo or Alpha Leonis, mag. +1.4) is in the position of the dot.

Mars had faded by about 0.3 magnitudes since the start of the apparition three months earlier. On September 17th Mars attained its faintest apparent magnitude of the apparition, at just +1.8. The planet now lay at a distance of 2.4521 AU from the Earth (366.8 million kms or 227.9 million miles) and its apparent diameter had increased slightly to 3".8. By this time the planet was rising in darkness from across the Northern hemisphere. Mars rose 3 hours ahead of the Sun at latitude 60° North, 2¼ hours before the Sun at latitude 40° North and 1½ hours before the Sun at the Equator. At Southern Tropical latitudes Mars rose in darkness about 1¼ hours before sunrise whilst at mid- and high-Southern latitudes the planet rose in twilight only an hour before sunrise. The planet's position in Western Leo meant that it rose in the ENE from most of the inhabited world, with the exception of high-Northern latitudes (i.e. further North than about 55° North) where the planet rose in the North-east.

On October 17th Mars passed 0°.4 North of Jupiter in the second planetary conjunction of the Martian apparition. Jupiter, at mag. -1.6, had emerged into the dawn sky in the early stage of its 2015-16 apparition. The two planets were positioned 40° West of the Sun at the moment of conjunction, with Venus (mag. -4.3) located 6°.6 to the West of the pair. For more details of this and the other planetary conjunctions which took place during this apparition, refer to the planetary conjunctions section below.

The following day (October 18th) Mars was involved in a rare occultation of a naked-eye magnitude star. At around 1924 UT the Red Planet occulted (passed in front of) the star  Leo (Chi Leonis, mag. +4.7), situated just ahead of the Lion's rear paw. The event, which lasted a maximum of about 2½ minutes, was visible in darkness from the Eastern seaboard of China, South Korea, Japan, the Southern Philippines (Mindanao) and Eastern Indonesia (Halmahera, Irian Jaya).

Over the next fortnight Mars, Jupiter and Venus formed a variety of geometric shapes in the night sky, clustered in Southern Leo, the two brightest naked-eye planets providing good pointers to the slowly-brightening Red Planet. On October 20th the three planets formed an East-West line some 5°.7 long, just South of the Lion's body. On October 23rd the three formed a low, flat isosceles triangle measuring 4°.6 wide at the base with sides 2°.3 long. Mars passed 0°.3 South of the star Leo (Sigma Leonis, mag. +4.0), at the foot of the Lion's hind leg, on October 25th. At around 03 hours UT on the following day (October 26th) Mars, Jupiter and Venus formed another isosceles triangle, this one lying on its side with a base measuring 1° wide and with sides of 3°.5. The triangle pointed East, towards the constellation of Virgo. Venus reached its greatest Western elongation (46° West of the Sun) at 10 hours UT on the same day. On October 28th the three planets formed another isosceles triangle, grouped around the Lion's rear paw, this time with a base 4°.6 wide and sides of 2°.5; this triangle was just 0°.9 high.

Mars entered Virgo, the Virgin, on November 2nd. In the early hours (UT) on November 3rd the three planets formed a long, 6°.9-high isosceles triangle, 0°.7 wide at the base, the apex pointing WNW towards Regulus. At around 16 hours UT on the same day Venus, moving direct (Eastwards) at an apparent daily rate of 0°.9 against the background stars, passed 0°.7 to the South of slower-moving Mars in the third planetary conjunction of the apparition. The two planets were positioned 46° West of the Sun, Venus having hardly changed its solar elongation since attaining greatest elongation eight days previously.

Mars' passage through the constellations during the early part of the 2015-17 apparition (i.e. pre star chart) is summarised in the table below:

By November 5th Mars and Venus had pulled sufficiently Eastwards from Jupiter so that no more geometric formations took place between the three. However, Mars, Venus and the star Zavijah ( Vir or Beta Virginis, mag. +3.6) formed an interesting straight line at around 17 hours UT on November 5th. The line, 1°.8 in length, was small enough to be contained within a telescopic wide-field (low magnification) eyepiece view and easily within a binocular field-of-view. Mars passed 0°.8 North of Zavijah itself on November 8th, then crossed the celestial equator (where the declination of a celestial body is 0°) heading Southwards on November 18th.

By mid-November, Mars had escaped the twilight and was rising in darkness from across the inhabited world, its solar elongation having reached 51°W. The Red Planet now rose around 5½ hours before the Sun at latitude 60º North; 4¼ hours before sunrise at 40º North; 3¼ hours before sunrise at the Equator and 2¼ hours before sunrise at 35º South. Since Mars now lay close to the celestial equator, it rose very close to due East across the inhabited world. At 60° North the planet attained a respectable 27° altitude before the dawn twilight enveloped it. At 40° North the planet attained an altitude of 38°; at the Equator it reached 39° whilst at 35° South the planet reached just 18° high.

Mars reached its most distant point from the Sun (called its aphelion) on November 20th, at a distance of 1.666 AU (249.2 million kms or 154.8 million miles).

Over the next month Mars passed the brighter stars which make up the Southern part of the Virgo figure, the planet entering the star chart coverage (above) in late November. On November 21st the planet passed 4° North of the star Zaniah ( Vir or Eta Virginis, mag. +3.8) then 1º.4 South of the double star Porrima or Arich ( Vir or Gamma Virginis, mag. +3.5) on December 1st.

In the early hours of December 6th the waning crescent Moon passed close by Mars and, in some regions of the world, passed in front of the planet (thereby blocking it from view) in an event called a lunar occultation. This particular occultation was seen in darkness from North-eastern Africa, Southern Arabia and the North-western Indian Ocean. From Addis Ababa in Ethiopia, Mars disappeared behind the Moon's bright limb at about 0015 UT (0315 local time) and re-appeared from behind the dark limb 1¼ hours later, at 0130 UT (0430 local time), the pair being positioned around 30º above the Eastern horizon (also see the Moon near Mars Dates section below).

By the end of the first week in December, the Red Planet had brightened to the upper threshold of second magnitude (+1.5) and its apparent diameter had increased to just under 5". Mars passed 0º.3 South of the star Theta Virginis ( Vir, mag. +4.4) on December 14th. One week later (December 21st) it passed 3º.8 North of the constellation's luminary named Spica ( Vir or Alpha Virginis, mag. +1.0), Mars being about 0.3 magnitudes fainter than the bright, blue-white star.

As 2016 commenced the Red Planet had reached a solar elongation of 70° West and had brightened to magnitude +1.0. As Mars entered Libra, the Balance, on January 17th, it was moving fractionally slower against the background stars (at 0°.5 per day) than at the commencement of the apparition some five months earlier. Mars passed 1°.2 North of the constellation's second-brightest star Zuben Elgenubi (² Lib or Alpha² Librae, mag. +2.8) on February 1st. At around 0930 UT on the same day, the Last Quarter Moon, Mars and the double-star Zuben Elgenubi formed an interesting line-up measuring 2°.9 across.

Mars reached western quadrature (90° West of the Sun) on February 7th, positioned 2º.8 ENE of Zuben Elgenubi. When seen from the Earth, the planet now showed its minimum phase (in this case, 90%) making it appear slightly gibbous when seen through telescopes. The illuminated section of the disk faced Eastwards, i.e. towards the Sun. The Martian disk appeared 7" across and shone at magnitude +0.7. Across the inhabited world, Mars was now rising in the ESE a little over 6 hours before sunrise. The altitudes attained by the planet before its dawn disappearance were: 13° (at 60° North), 33° (at 40° North), 74° (at the Equator) and 65° (at 35° South). Between latitudes 10º North and 75º North, the planet transited the local meridian (i.e. it passed through its highest point in the South) a short while before disappearance. South of 10º North, the dawn twilight washed out the planet before it reached the meridian. Mars was now brightening significantly with each passing week, its pale-orange coloration seemingly more obvious than in the preceding months. Also on February 7th, Mars passed 9º.4 North of the star Brachium or Zuben Algubi ( Lib or Sigma Librae, mag. +3.3).

Mars reached magnitude +0.5 on February 19th, technically making it a zeroth-magnitude object. On February 25th the planet passed 3º.1 South of the star Zuben Elakrab ( Lib or Gamma Librae, mag. +4.0) and then 2º.2 South of the star Theta Librae ( Lib, mag. +4.1) on March 7th. Mars passed 3º.2 North of Dschubba ( Sco or Delta Scorpii, mag. +2.2), in the neighbouring constellation of Scorpius, the Scorpion, on March 12th, the planet attaining magnitude -0.0 ('minus zeroth magnitude') on the same day.

Mars entered Scorpius on March 13th, reaching 10".0 in angular diameter three days later, positioned about 115° West of the Sun. For telescopic observers, the planet was now at a sufficient apparent size for significant surface detail to be seen and for a regular campaign of observing to commence.

Mars passed just 8' (8 arcminutes, where 1' = 1/60th of a degree) North of the double-star Graffias (¹ Sco or Beta-1 Scorpii, combined mag. +2.6) on March 16th. The two blue-white components (¹ Sco and ² Sco) are magnitudes +2.6 and +4.9, separated by 13".7 and are easily seen in small telescopes. Beta-1 Scorpii is itself also double, having a tenth-magnitude companion positioned less than an arcsecond away, separable only in larger telescopes. The Mars-Graffias passage was best seen from North-west Africa, Southern Europe, the Atlantic Ocean and the Eastern half of South America. A simulated telescope view of the event is shown in the graphic below.

Over the course of eleven hours on March 17th, the planet passed North of the two Omegan stars Jabhat al Akrab (¹ Sco or Omega-1 Scorpii, mag. +3.9) and Omega-2 Scorpii (² Sco, mag. +4.3). The two stars are separated in the night sky by 0º.24 and they lie very close to the ecliptic (the path of the Sun, which the Moon and planets follow very closely). Consequently, one or other of these stars is often occulted by the Moon and, much more rarely, by planets (Venus will next occult ² Sco in the year 2038). On this occasion, Mars passed 0º.9 North of the blue-white star Jabhat al Akrab (Arabic for 'forehead of the Scorpion') at 05 hours UT and 1º.1 North of the yellow star Omega 2 Scorpii at 16 hours UT.

Situated a few degrees to the North-east of the two Omegan stars is the star Jabbah ( Sco or Nu Scorpii, mag. +4.0). It is a quadruple star, i.e. it appears as a blue-white double-star through small telescopes, but larger telescopes reveal each of its component stars to be double. Mars passed 0º.5 South of Jabbah on March 21st.

On March 26th Mars, now at magnitude -0.4, passed 2º.6 North of the eighth-magnitude globular cluster M80 (or NGC 6093) which, like most of the brighter globulars, appears as a faint, circular, fuzzy spot of light through binoculars under dark skies. The narrow separation allowed the two objects to be contained within the eyepiece view of a wide-field, low-magnification ocular, whilst binocular users saw the planet and cluster appear in very close proximity.

Now approaching the Eastern border of Scorpius, Mars passed 5º North of the variable star Alniyat ( Sco or Sigma Scorpii, mag. +2.9) on March 31st, the planet now having brightened to magnitude -0.5 ('minus first magnitude') and its apparent daily motion having slowed dramatically to just 0º.1. Mars entered Ophiuchus, the Serpent-Bearer, on April 3rd, a constellation which is famous (or rather, infamous!) for its absence from the astrological list of zodiac constellations. Its original name was Serpentarius, although today this is almost never used. Ophiuchus is a large, unwieldy constellation, occupying 948 square degrees of sky, but only its narrower, Southern section is crossed by the ecliptic.

By mid-April the planet had brightened a further half-magnitude to -1.0. On April 17th Mars' Eastward (direct) motion ceased when it reached its eastern stationary point, positioned 5º.2 North of the Scorpion's brightest star Antares ( Sco or Alpha Scorpii, mag. +1.0v). Hereafter the planet's motion became retrograde (Westward), a situation which would continue over the next 2½ months. Antares is unmistakable in that it scintillates (twinkles) orange-red, rivalling the colour of the Red Planet - indeed, the name Antares derives from the ancient Greek 'anti Ares' meaning 'rival of Mars' (Ares being the ancient Greek God of War). The two celestial bodies' brightnesses differed on this occasion by two magnitudes, Antares being obviously the fainter of the two.

Mars crossed the ecliptic in a Southward direction on April 28th, positioned close to Ophiuchus' Western border with Scorpius. The planet's ecliptic crossing at this point was significant because it determined the shape of the loop described during the months around its opposition. Essentially, whenever a superior planet crosses the ecliptic near the time of its opposition to the Sun, the path described by the planet against the background stars will take the form of a zig-zag, i.e. either an 'S-shape' or a 'Z-shape' (as opposed to the standard loop). The zig-zag will be Northward-facing ('Z-shaped') when the planet moves to the North of the ecliptic and Southward-facing ('S-shaped') when it moves to the South of the ecliptic. In the present situation - as can be seen in the star chart above - Mars described a Southward-facing zig-zag over the period in question (for more information on the loops and zig-zags described by the planets in the night sky, see the Planet Movements page).

From around late April, with the planet's elongation having increased to around 140º, the lengthening Northern summer twilight began to interfere with observation from latitudes North of about 60º North. In early May, observers at 60º North were only able to view the planet for about 4 hours, the entire visible period taking place in advanced twilight.

Mars moved back into Scorpius on April 30th and soon afterwards began to pass the stars it had already passed in the previous two months, except in reverse order. Mars passed 3º.9 North of Alniyat ( Sco) on May 3rd; 1º.2 North of the globular cluster M80 on May 7th and 2º.2 South of Jabbah ( Sco) on May 11th. On May 15th Mars passed the two Omegan stars ¹ Sco and ² Sco again; 0º.8 South of ² Sco at 04 hours UT and 1º.0 South of ¹ Sco at 14 hours UT. May 16th saw the planet passing 1º.8 South of Graffias ( Sco) and May 20th saw it pass 0º.9 North of Dschubba ( Sco).

At 2022 UT on May 21st the Full Moon passed several degrees to the North of a now very bright Mars (mag. -2.0), an event which provided an excellent opportunity for astrophotographers. Due to the effect of parallax, the angular separation between the two celestial bodies depended upon the observer's location on Earth. The separation between Mars and the Moon varied on this occasion from 5º.1 (at higher Northern latitudes) to 6º.5 (at mid-Southern latitudes), the best views of the pairing being from Southern Europe, the Middle East, Southern and Eastern Africa, India and the Indian Ocean (also see the Moon near Mars Dates section below).

Mars reached opposition to the Sun at 11 hours UT on May 22nd 2016, at which point it was directly opposite the Sun in the sky (solar elongation = 180°) and at its brightest for this apparition. The planet was positioned 1º.3 WNW of Dschubba, 4º.8 South of Theta Librae ( Lib) and 8º.8 North-west of Antares. This was not, however, Mars' closest point to the Earth during this apparition; because of the eccentricity of its orbit, Mars' periareion (its closest point to Earth) was reached eight days later - on May 30th - when it was 0.5032 AU distant (75.2 million kms or 46.7 million miles), i.e. about 935,600 kms (581,300 miles) closer than on opposition day. The Red Planet now shone at magnitude -2.05 and its apparent size was 18".3, i.e. double the size it was in early March and triple the size it had been in mid-January. On opposition day Mars was creeping slowly Westward against the stars of Scorpius at a rate of about 0º.3 per day. At opposition, a superior planet rises around sunset, is visible throughout the night and sets around sunrise. Its highest point in the sky is reached when it crossed the observer's meridian at local midnight (due South at midnight in the Northern hemisphere; due North at midnight in the Southern hemisphere).

On opposition day, the Red Planet was experiencing late Summer in its Northern hemisphere and late Winter in its Southern hemisphere. The planet's Northern polar axis was tipped towards the Earth at an angle of about 10º, giving us a good view of its Northern Polar Cap (NPC). Mars was positioned at a heliocentric longitude of 241º ( = 241°) and the areocentric longitude of the Sun (L_s) was 156°. The Martian Year was 33, the Martian Month was 6 and opposition day equated to Sol Number 330 on Mars. The equivalent Earth date on Mars - called the Martian Date (MD) - was September 19th. All the terms given in this paragraph are explained in more detail on the Martian seasons page.

At the 2016 opposition, Mars was 0.6 magnitudes brighter (nearly two times brighter) than it was at its previous opposition in April 2014 and its apparent disk diameter was about 20% larger. Mars had almost ended its run of poor (i.e. distant) oppositions which had resulted in small disk diameters (less than about 20" across) since the opposition of December 2007. Such distant and dim oppositions, taking place when the planet is near the aphelion position in its orbit, are often referred to as aphelic oppositions. The 2016 opposition of Mars was, however, a relatively good one, lying in the middle-ground between an aphelic and a perihelic opposition (for more details, see the Mars Oppositions page).

Opposition having passed, the solar elongation moved from Westerly to Easterly and the magnitude of the angle reduced. Mars' solar elongation reduced from 180° (on opposition day) to 170° East of the Sun one week later, on May 29th. Mars passed 4º.8 South of Theta Librae ( Lib) for a second time on May 24th. The planet's retrograde motion carried it back into Libra itself on May 28th, reaching periareion (see above) two days later. On June 6th Mars passed 6º.3 South of Zuben Elakrab ( Lib), reaching its western stationary point, 5º.4 NNE of Brachium ( Lib), on June 30th. The planet's motion now returned to 'normal' (direct) and continued as such through the remainder of the apparition.

Seen from high-Northern latitudes, the 'visibility window' of Mars had been rapidly closing and from early July, observers North of about 60º North lost sight of the planet completely in the bright summer twilight, which now lasted throughout the night. Observers in these high latitudes did not see Mars again until late September, by which time the planet had moved on South-eastwards to the Southernmost point of the zodiac.

Now moving direct and having faded to magnitude -1.0, Mars once again passed the stars it had already passed (twice) since late February. Although occupying the same band of Right Ascension (celestial longitude) as it did five months earlier, the wide and open 'S-curve' described by the planet had now placed it over 4º further South than it was back then. Hence on July 25th the planet passed 7º.4 South of Zuben Elakrab ( Lib), some 4º.3 further South than its February 25th passage (see above).

Mars re-entered Scorpius on August 2nd, passing 6º.4 South of Theta Librae ( Lib) on August 6th. Again, this was 4º.2 further South than its March 7th passage of this star and 1º.6 further South than its May 24th (retrograde) passage. On August 10th the planet passed 0º.8 South of Dschubba ( Sco), a full 4º further South than its March 12th passage of this star and 1º.7 further South than its May 20th (retrograde) passage. On both of these previous occasions Mars was positioned to the North of Dschubba, whereas it was now to the South of it.

By mid-August Mars had faded back to 'minus zeroth magnitude' (-0.5) and its apparent diameter had shrunk by a third since opposition. On August 12th the planet passed 3º.9 South of the double-star Graffias ( Sco) once more, then on the following day encountered the Omegan stars ¹ Sco and ² Sco again, on this occasion at a wider separation than previously. Mars passed 3º.1 South of ¹ Sco at 12 hours UT and 2º.9 South of ² Sco at 19 hours UT.

Mars passed 1º.2 South of the globular cluster M80 on August 18th, the same distance from the cluster that it passed whilst moving North of it on May 7th. Finally, the planet passed 1º.2 North of Alniyat ( Sco) on August 20th, its solar elongation having now reduced below 100º.

On August 21st, Mars re-entered Ophiuchus. Over the next five days the planet would pass a globular cluster, a red giant star and a ringed planet. Soon after crossing the border Mars passed 2º.1 North of the globular cluster M4 (NGC 6121), a 7th-magnitude cluster in Scorpius which is visible through binoculars under truly dark skies. Being so close to Antares it is easy to find and, being some 20' in diameter, is wonderfully resolved through telescopes. It is not a particularly concentrated cluster but has an eye-catching central 'bar' of faint stars running vertically through its centre.

On August 24th Mars passed 1º.8 North of Antares ( Sco) itself, providing a good opportunity to compare the colours of the two objects by naked-eye. Now at magnitude -0.4, Mars was 1.4 magnitudes (around 3½ times) brighter than the star which, one could argue, did not really make for a fair comparison. The situation was made more difficult by the fact that Mars, being a planet, shines with a steady light, whilst Antares, being a stellar point-source, scintillated considerably (paricularly from higher Northern hemisphere latitudes, where the star transits at a low elevation).

Mars experienced its fourth planetary conjunction of the apparition on August 25th, when it passed 4º.4 South of Saturn. This wide conjunction was best seen from the Southern hemisphere, the planets differing by 0.9 magnitudes. The event took place in late summer in the Northern hemisphere, positioning the two planets low above the South-western horizon at dusk and poorly placed for observation. Saturn had faded since reaching opposition the previous June although its wide-open rings continued to make it a nice telescopic sight.

At around 18 hours UT on August 27th Mars re-entered Scorpius at a shallow angle to the North-east of Antares, returning to Ophiuchus six days later on September 2nd.

Mars passed 0º.8 North of the seventh-magnitude globular cluster M19 (NGC 6273) on September 6th. At around 12' in diameter, it is a roughly oval-shaped 'fuzzball' of stars which can easily be seen through binoculars and small telescopes.

Mars reached eastern quadrature (90º East of the Sun) on September 13th, positioned 11º.1 East of Antares. Like at western quadrature back in February, the planet again showed a minimal phase - in this case, 84% - making it appear slightly gibbous when seen through telescopes. Unlike at western quadrature, the illuminated part of the planet's disk faced Westwards (not Eastwards, as before) because it was now positioned to the East of the Sun when seen from the Earth.

On September 14th Mars passed 0º.7 South of Ophiuchus' Southernmost bright star Theta Ophiuchi ( Oph, mag. +3.2), leaving the constellation on September 22nd when it entered Sagittarius, the Archer. Now four months after opposition, the planet was moving a tad faster against the background stars than it was four months before opposition. Back in mid-January the planet was moving Eastwards at a rate of 0°.53 per day but now it was moving Eastwards at 0°.64 per day; so the planet exited the 'S-curve' at a faster speed than it entered.

By the third week of September the planet's apparent diameter had reduced to just 9".3 - only half that at its closest approach back in late May. Mars attained its most Southerly declination for this apparition, at -25° 54' 37" (-25°.91 in decimal format) on September 23rd, which was the furthest South the planet had been positioned since 2001. The planet now set at its most Southerly position on the local horizon. Typically this will be towards the South-west at latitudes far away from the Equator and towards the WSW at Equatorial latitudes. Mars now set 2 hours after the Sun (at 60º North), 4¼ hours after the Sun (40º North), 5¾ hours after the Sun (Equator) and 7 hours after the Sun (35º South).

By late September Mars' apparent magnitude had returned to positive (+0.0). Between September 28th and 29th, it passed 1º.5 South of the sixth-magnitude gaseous nebula labelled M8 (NGC 6523) and commonly called the Lagoon Nebula. With an apparent dimension of 90' by 40', the planet took 29 hours to traverse the width of the nebula (from 11 hours UT on September 28th to 16 hours UT on the 29th). The planet was now seen amidst the backdrop of a very star-rich region of the Milky Way galaxy, only 5º degrees away from its true centre.

From around late September, observers situated North of ca. 60º North, who lost sight of the planet in mid-July, now began to detect it once more, low down in the SSW after sunset.

Over the next few weeks Mars passed the numerous bright stars which define the shape of Sagittarius' Archer figure, along with four globular clusters, which are particularly numerous in this region of the night sky. Between September 29th and October 19th the planet passed just to the North of the constellation's famous asterism, the Teapot. It is bounded by eight stars (which taken counter-clockwise are: Nash, Kaus Meridionalis, Kaus Borealis, Phi Sagittarii, Nunki, Tau Sagittarii, Ascella and Kaus Australis). The Teapot is supposedly pouring its contents over the tail of the Scorpion and the steam rising from its spout is said to be marked by a particularly dense and misty stretch of the Milky Way. The path of Mars on this occasion just clipped the top of the teapot.

On September 29th Mars passed 4º.6 North of the star Nash or Al Nasl ( Sgr or Gamma Sagittarii, mag. +3.0). At around 2050 UT on the following day the planet passed just 4'.8 (4.8 arcminutes) North of the 8th-magnitude globular cluster NGC 6553 (apparent diameter 8'.1), a cluster which is only seen well in larger telescopes. On October 4th the planet passed 4º.1 North of the star Kaus Meridionalis ( Sgr or Delta Sagittarii, mag. +2.7) which marks the centre of the Archer's bow. The next day (5th) Mars passed 0º.8 South of another globular cluster, M28 (NGC 6626), of 7th-magnitude and with an apparent diameter of 11'.2. On October 7th Mars passed just 11' (11 arcminutes or 0º.2) South of the orange star Kaus Borealis ( Sgr or Lambda Sagittarii, mag. +2.8) which marks the top of the Teapot asterism (and incidentally, the top of the Archer's bow, which points West). At 0320 UT on October 8th the Red Planet passed a mere 3'.5 (3.5 arcminutes or 0º.05) South of the faint, 9th-magnitude globular cluster NGC 6638 (visible in darkness from the Eastern Pacific Ocean and its seaboard). This is another difficult and concentrated globular, 5' in diameter, which is only well resolved in larger optical instruments (a simulation of the view through an astronomical telescope is shown below). On October 9th the planet passed 1º.5 South of the much brighter globular cluster M22 (NGC 6656) which is considered to be one of the finest globulars in the night sky. Its integrated magnitude is about +5.9 and it has an apparent diameter of 24'. It is just visible to the naked-eye from dark sites, is easily seen through binoculars and is a spectacular sight through telescopes.

The four stars passed by Mars over the next week form the 'handle' of the Teapot. The planet passed 1°.7 North of Phi Sagittarii ( Sgr, mag. +3.1) on October 13th; 1°.2 North of the constellation's second-brightest star Nunki ( Sgr or Sigma Sagittarii, mag. +2.0) on October 16th; 5°.0 North of Ascella ( Sgr or Zeta Sagittarii, mag. +2.6) on October 18th and finally, 3º.0 North of Tau Sagittarii ( Sgr, mag. +3.3) on October 19th.

Now clear of the brighter stars of Sagittarius, Mars continued on its Eastward course, passing 1°.3 North of 52 Sagittarii (mag. +4.6) on October 29th and, on the same day, reaching perihelion (its closest orbital position to the Sun) at a distance of 1.3812 AU (206.6 million kms or 128.4 million miles) from the Sun. On November 7th the planet passed 5°.4 North of the star Terebellum (62 Sgr, mag. +4.5), at the far Eastern edge of the constellation. Shortly afterwards, the planet exited the star chart coverage.

There are simply too many globular clusters in Sagittarius for Mars to have left the constellation without passing another one(!) and so, at 04 hours UT on November 8th, the planet passed 13' (13 arcminutes) South of M75 (NGC 6864). This distant and compact 8th-magnitude cluster has an apparent diameter of only 6' and lies just 0°.3 from the Eastern edge of the constellation. Ten hours later Mars left Sagittarius and entered Capricornus, the Sea-Goat.

Mars passed 6º.4 South of the star Dabih ( Cap or Beta Capricorni, mag. +3.0) on November 13th and 0º.9 South of Theta Capricorni ( Cap, mag. +4.0) on November 27th. On December 3rd, at about 0817 UT,  the planet passed a very close 44".7 (44.7 arcseconds) South of the star Iota Capricorni ( Cap, mag. +4.3). This is so close together that the naked-eye could not split the two; they effectively appeared as one 'star'. Through binoculars and telescopes at low magnification the pair appeared as a temporary 'double-star' with components of magnitude +0.7 and +4.3, Iota Capricorni appearing pale yellow and Mars, of course, pale orange. On December 9th, Mars passed 1º.3 North of Nashira ( Cap or Gamma Capricorni, mag. +3.7) and finally, on December 11th it passed 1º.4 North of the constellation's brightest star, a variable star named Deneb Algiedi ( Cap or Delta Capricorni, mag. +2.9v).

By the middle of December Mars was setting around 6 hours after the Sun at latitude 60º North, 5 hours after the Sun at latitude 40º North, 4½ hours after sunset at the Equator and 4 hours after sunset at latitude 35º South. Being positioned some 10º South of the celestial equator, the planet set in the WSW across the inhabited world. The altitudes of the planet, as it became visible in the dusk twilight, were: 16° (at 60° North), 35° (at 40° North), 55° (at the Equator) and 38° (at 35° South). Between latitudes 56° North and 76° North Mars transited soon after it appeared in the dusk twilight; elsewhere, the planet had already passed the meridian when it was first glimpsed.

The Red Planet entered Aquarius, the Water-Carrier, on December 15th, passing 1º.0 North of the star Iota Aquarii ( Aqr, mag. +4.2) on December 18th. Four days later (22nd) Mars passed 4º.0 South of the star Ancha ( Aqr or Theta Aquarii, mag. +4.1). Between December 23rd and 28th the planet was positioned about 10º South of Aquarius' best-known identifier, the so-called 'Steering Wheel' asterism (a star chart showing this region of the night sky can be found on the Neptune page).

With the arrival of 2017, Mars was involved in its closest planetary conjunction with Neptune for over seven centuries! At 0637 hours UT on January 1st Mars, now at magnitude +0.9 and less than 6" across, passed just 1'.2 (1.2 arcminutes or 0º.02) South of Neptune, at mag. +7.9. The closeness of the two planets - easily contained within the field-of-view of telescopes at high magnifications - made it an ideal opportunity for those who have never seen our most distant Solar System planet to locate it with relative ease, using Mars as a bright locator-beacon. This most proximate of evening conjunctions was ideally placed for Northern hemisphere observers, the two planets being positioned 58º away from the Sun.

Two days later, at 0511 hours UT on January 3rd, the five-day old waxing crescent Moon, Mars and Neptune formed a tight trio 1º.4 across in central Aquarius. The trio was not wholly naked-eye of course (since Neptune was involved) however this was a potentially interesting grouping to observe through small telescopes at low magnification. The grouping was best seen from the central Pacific Ocean, where the Moon was also seen to occult the two planets in turn. From the islands of Kaua'i (Hawaii) and Necker Island (Leeward Islands), where it was evening on January 2nd (local time), a lunar occultation of Neptune was in progress as dusk fell. Neptune re-appeared in darkness behind the bright limb of the Moon, then two hours later the dark limb of the Moon occulted Mars. Thirteen hours after this interesting event - the Moon now having moved on North-eastwards - Mars passed 0º.4 South of the star Lambda Aquarii ( Aqr, mag. +3.9).

On January 11th the planet passed 0º.4 North of the star Phi Aquarii ( Aqr, mag. +4.2) and, on January 13th, 1'.7 (1.7 arcminutes or 0º.02) North of the star 96 Aquarii (96 Aqr, mag. +5.7). Both of these stars lie quite close to the ecliptic and, like the Omegan stars in Scorpius (see above), they are sometimes occulted by passing planets. Phi Aquarii will next be occulted by Venus in the year 2028 and 96 Aquarii will next be occulted by Mars in 2032.

From January 12th through to the 23rd, Mars, now mag. +1.0, was positioned about 7º South of the Circlet of Pisces, at the Western end of Pisces, the Fishes. The Circlet comprises six stars of fourth and fifth magnitude; under light-polluted conditions it is likely that some or all of them will not be seen with the naked-eye. Mars entered Pisces on January 19th.

From around the third week of January, Venus approached Mars from the West, though the two planets did not reach conjunction on this occasion. Venus was now about three-quarters of the way through its 2016-17 evening apparition and reached its greatest Eastern elongation (its maximum angle East of the Sun) on January 12th. Over the next few weeks Venus curved against the stars to the West of Mars, moving from direct to retrograde motion, initially getting closer to Mars but then pulling away from it. Venus was positioned 6º.6 to the WSW of Mars on 21st January, 5º.4 West of it from February 2nd-3rd (its closest point to the Red Planet) and 5º.9 to its WNW on February 10th.

Mars crossed the celestial equator ( = 0°) heading Northwards on January 29th, positioned to the South-east of the Circlet of Pisces. The planet's apparent diameter fell below 5" on February 3rd. Mars briefly exited Pisces at 01 hours UT on February 7th when it entered the constellation of Cetus, the Whale, clipping its North-western corner. Over the next 11½ hours Mars was technically outside the zodiac, traversing a stretch of Cetan sky just 0º.3 wide (measured South-east to North-west) before re-entering Pisces at 12 hours UT on the same day. This translated into a daily apparent motion of about 0º.6 against the background stars.

Mars passed 2º.5 South of the star Delta Piscium ( Psc, mag. +4.4), about half-way along the Southern Fish's body, on February 15th and then 1º.2 South of the star Epsilon Piscium ( Psc, mag. +4.3) on February 20th. At 1233 UT on February 24th the planet passed just 11'.6 (11.6 arcminutes or 0º.2) North of Zeta Piscium ( Psc), a double-star with components of mag. +5.6 and +6.5, separated by a distance of 22".8. Much like the planet's close passage of Iota Capricorni ( Cap) on December 3rd 2016 (see above), Mars, now at mag. +1.2, appeared to the naked-eye as the brighter component of a 'double-star', the fainter component (i.e. Psc) itself appearing as a single white star of mag. +4.9. The separation of the two (11'.6) was nearly the same as that between the stars Mizar ( UMa or Zeta Ursae Majoris, mag. +2.0) and Alcor (80 UMa, mag. +4.0), the famed double-star in Ursa Major, positioned at the bend of the Big Dipper's 'arm'. Mizar and Alcor have historically been considered a good test of one's eyesight, since the limit of the average naked-eye's acuity is generally thought to be about 5' (5 arcminutes, or 0º.08).

At around 05 hours UT on February 27th Mars crossed the ecliptic heading Northwards, then just 3½ hours later passed 0º.6 North of the planet Uranus in the Red Planet's last planetary conjunction of this apparition. Much like its conjunction with Neptune in January, this evening conjunction in Pisces was ideally placed for Northern hemisphere observers, although the narrower solar elongation (43º East) meant that the two planets were positioned slightly lower in the sky after sunset and were visible for a shorter period before they set. At magnitude +5.9 Uranus was at the limit of naked-eye visibility whilst Mars had faded to mag. +1.3. The two were close enough to be contained within a wide-angle telescope eyepiece view, and were easily seen in binoculars.

Seen from latitudes South of about 43º South, Mars' narrowing solar elongation, its low altitude and the local twilight reduced the 'observing window' of the planet to just 1½ hours from around late February. Elsewhere the planet was now setting 4½ hours after the Sun (at latitude 60º North), 3½ hours after sunset (at 40º North), 2½ hours after sunset (at the Equator) and about 1¾ hours after sunset (at 35º South). Mars set in the WNW in the Northern hemisphere and in the West in the Southern hemisphere. At latitude 60° North Mars stood 26° above the horizon when it first became visible at dusk - a significant improvement on previous months, caused by the improved angle of the ecliptic to the local horizon after sunset. Elsewhere the altitude of the planet was beginning to fall as its solar elongation fell below 45°. At 40° North it was 33° high at dusk; at the Equator it stood 32° high whilst at 35° South it was only 14° above the horizon.

At around 04 hours UT on March 8th, Mars passed 1º.8 North of the star Torcularis Septentrionalis ( Psc or Omicron Piscium, mag. +4.2) in the tail of the Northern Fish. The fanciful name, which is Latin for 'North Press', first appeared in the 1515 edition of the star catalogue Almagest. It was a translation of the Greek word '' meaning 'winepress'. However, this was a mistranslation of the original Greek word '' meaning 'flax', i.e. the cord that tied the two fishes' tails together.

Ten hours after passing Torcularis, Mars entered the constellation of Aries, the Ram. The planet passed 7º.4 South of the double-star Mesarthim ( Ari or Gamma Arietis, mag. +3.9) on March 11th and later that same day, 8º.7 South of the star Sheratan ( Ari or Beta Arietis, mag. +2.6). Aries' brightest star Hamal ( Ari or Alpha Arietis, mag. +2.0) was passed by the planet five days later (March 16th) at an angular distance of 10º.3. Mars' uneventful passage through this small constellation continued with the passage of two fourth-magnitude stars in the Eastern half of the Ram: 3º.8 to the South of Epsilon Arietis ( Ari, mag. +4.6) on April 3rd and 1º.4 South of Botein ( Ari or Delta Arietis, mag. +4.3) on April 8th. The following day, Mars faded below the threshold of second magnitude, at +1.5.

Mars entered Taurus, the Bull, on April 12th - although the Red Planet was not quite done with Aries yet. Two days later, at about 0310 UT, it left Taurus and re-entered Aries, traversing a WSW-ENE path just 5'.5 (5.5 arcminutes) long. A little over three hours later, at 0620 UT, Mars re-entered Taurus; this equated to an apparent daily motion of 0º.7 against the background stars. The planet was now only 30º from the Sun, had an apparent magnitude of +1.5 and an apparent diameter of just 4".

Between April 19th and 21st Mars passed around 3°.5 South of the constellation's most famous star grouping known as the Pleiades (pronounced 'PLY-add-eez' or 'PLEE-add-eez'), also called the Seven Sisters (M45). The cluster would normally make for an interesting photographic subject, however its low altitude at dusk severely limited the observing time. As they became fully visible the Pleiades stood between 7° high (at 60° North and 25° South) and 13° high (at 30° North) in the North-west (60° North) or the WNW (elsewhere). The orientation of the cluster - and the Red Planet's position in relation to it - varied according to the observers's latitude. Around latitude 9° North Mars and the cluster appeared at roughly the same elevation at dusk; North of this latitude, the cluster was positioned to the upper-right of the planet, whilst South of this latitude it was positioned to the lower-right. South of ca. latitude 27° South the Pleiades were too low down to observe at this time.

From around late April, twilight began to interfere with observation of Mars as seen from latitudes North of ca. 60° North. At these latitudes the planet was visible for around 3 hours before setting in the North-west, the planet being in twilight throughout. Elsewhere the planet was setting in darkness towards the WNW. At latitude 40° North, Mars set about 2¼ hours after sunset and at the Equator it set around 1¾ hours after sunset. At mid-Southern latitudes the planet set just 1¼ hours after the Sun.

During the first week of May, Mars passed around 5°.3 North of a much larger star cluster called the Hyades. The group was rather too widely scattered to form part of Charles Messier's catalogue, so it has no Messier number, however it is sometimes referred to under the moniker of Melotte 25 (after the British astronomer Philibert Jacques Melotte, who published his catalogue of 215 globular and open clusters in 1915). The Hyades is a distinct 'V'-shaped grouping of stars which form the head of the Bull. At the apex of the 'V' is a star known variously as Prima Hyadum, Primus Hyadum or Hyadum I ( Tau or Gamma Tauri, mag. +3.6). The name means 'First Hyad' or 'Chief of the Hyades', the Hyades being the daughters of Atlas and Aethra in Greek mythology. Mars passed 6°.5 North of the star on May 1st. Hyadum II (¹ Tau or Delta-1 Tauri, mag. +3.7) is a triple star system positioned roughly mid-way along the Northern arm of the 'V' (the Bull's forehead). Its name means 'Second Hyad' (therefore, linguistically it should be named Secundus Hyadum). Mars passed 4°.7 North of this star on May 2nd.

At the South-eastern corner of the Hyades, marking the 'eye' of the Bull, is the orange-red star Aldebaran ( Tau or Alpha Tauri, mag. +0.9). Its coloration derives from the fact that it is a red giant star. Most of the Hyades stars comprise a genuine cluster, moving through space together, however Aldebaran is not part of the group; it is a foreground star, positioned closer to the Earth than the cluster. Mars passed 6°.2 North of Aldebaran on May 7th.

At 1144 UT on May 9th the Red Planet made another close passage of a star: this time, just 24".7 (24.7 arcseconds or 0'.4) North of the triple-star Tau Tauri ( Tau, mag. +4.2), which is positioned at the 'bend' of the Bull's Northern horn. The distance between planet and star equated to just six apparent Mars-diameters, although the Red Planet was eleven times brighter than the star. Tau Tauri A is a blue-white star with a seventh-magnitude white or lilac companion, Tau Tauri C, positioned just over 1' (1 arcminute) away to its South-west (Tau Tauri B is an eighth-magnitude companion of the primary star, too close for amateur telescopes to split). Interestingly, the distance at which Mars passed the primary star (Tau Tauri A) was a little over one-third of the apparent distance between Tau Tauri A and Tau Tauri C, although unfortunately in this instance, the planet and Tau Tauri C were not in the same direction.

Around mid-May, observers situated at high Northern and Southern latitudes were the first to bid farewell to the Red Planet as it slipped into the dusk twilight. Over the next two weeks the 2015-17 Martian apparition also closed for observers situated North of about 45° North.

On May 24th Mars passed 4°.5 South of the star Al Nath or El Nath ( Tau or Beta Tauri, mag. +1.6) which marks the tip of the Bull's Northern horn. The star also carries the name Gamma Aurigae ( Aur) since, apart from defining one of the Bull's horns, it also neatly completes the six-sided figure comprising the stars of Auriga, the Charioteer, located to the North-east of Taurus. The star marking the tip of the Bull's Southern horn is Zeta Tauri ( Tau, mag. +2.9v) and Mars passed 3°.0 North of it on May 28th. With its return to the vicinity of North-eastern Taurus, Mars had now completed a full circuit of the zodiac since the start of its 2015-17 apparition nearly two years earlier.

On June 5th the Red Planet entered Gemini, the Twins, and one day later it attained its most Northerly declination for this apparition ( = +24° 19' 43" or +24°.32). For those latitudes which could still see it, the planet now set at its most Northerly point along the local horizon, the actual point of setting depending upon the observer's latitude. By the end of the first week of June Mars only remained visible between latitudes 40° North and 30° South, setting towards the WNW throughout.

Mars' passage through the constellations during the latter (i.e. post star chart) period of the 2015-17 apparition is summarised in the table below:

As Mars' solar elongation reduced below 15º East of the Sun in mid-June, the planet finally became lost from view from across the inhabited world, bringing the 2015-17 apparition to a close. Mars remained out of view - lost in the solar glare - for around 2½ months as it continued Eastwards on the far side of its orbit from the Earth. Mars reached superior conjunction (passing behind the Sun as viewed from the Earth) in Western Cancer on July 27th, when it was 2.6553 AU (397.2 million kms or 246.8 million miles) from Earth. Had the planet been visible from Earth at this time, it would have shone at magnitude +1.7 and appeared just 3".5 across.

Mars became visible from the Earth again in the Eastern sky at dawn from around late August 2017, when it was first glimpsed from Northern Tropical latitudes. This heralded the start of the much-awaited 2017-19 apparition, which will see Mars pass at its closest point to the Earth since 2003 when it next reaches opposition in Capricornus in July 2018.

 [Terms in yellow italics are explained in greater detail in an associated article describing planetary movements in the night sky.]

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Mars Conjunctions with other Planets, 2015 to 2017

During the 2015-17 apparition, all except one of the six visible conjunctions took place at solar elongations of less than 58°, Mars being fainter than magnitude +0.8 in all five cases. Four of the six conjunctions favoured the Northern hemisphere, these being evenly divided between morning and evening viewings. Rather unusually, Mars had no visible conjunctions with the planet Mercury during this apparition.

The most interesting Martian conjunction of the 2015-17 apparition was that with Saturn in the evening sky on August 25th 2016. Taking place in Southern Ophiuchus just three months after both planets' opposition dates, it was also the brightest of the six conjunctions, Mars and Saturn being at either end of 'zeroth magnitude'. This was the only conjunction of the six which truly favoured the Southern hemisphere. At the moment of their first appearance at dusk, the two planets were positioned at the zenith (directly overhead) at 25° South, 80° above the Northern horizon at 35° South and 70° above the Northern horizon at 45° South. Despite the relatively wide solar elongation of 97°, twilight and low altitude interfered with observation from mid- and high-Northern latitudes. This was caused by the dual effect of the planets' high Southerly declinations and the shallow angle of the ecliptic to the local horizon after sunset at this time of year. On this occasion Mars and Saturn were separated by a wide 4º.4, so that they were too far apart to fit within a telescopic field of view but were well within the typical view of binoculars. In 2016 the pair only narrowly missed out on multiple conjunction events (i.e. double or triple conjunctions) because the planets' loops did not overlap in longitude.

There were two conjunctions with Venus during the apparition, both being morning events in 2015. The conjunction of November 3rd was ideally placed for Northern hemisphere observers, the planets' location in Virgo positioning the ecliptic at a steep angle to the local horizon at dawn. This conjunction was less well-seen in the Southern hemisphere, being visible in twilight at around 35° South and not visible at all South of latitude 49° South. A poor, nine-degree wide conjunction between Venus and Mars at dawn on August 29th was only visible South of mid-Northern latitudes and North of mid-Southern latitudes.

Mars was involved in a close morning conjunction with Jupiter in central Southern Leo on October 17th 2015. Seen from the Northern hemisphere, the planets reached a respectable altitude in the Eastern sky before the Red Planet succumbed to the dawn twilight. At latitude 50° North the planets attained an altitude of 27° before Mars was lost from view whilst at 20° North they reached 31°. Adding brilliance to the event, shining at magnitude -4.3, was morning star Venus, positioned 6½° away to the West of the pair. The conjunction was seen in twilight from mid-Southern latitudes, reaching only 16° above the horizon at latitude 25° South and just 8° at 40° South.

The final two conjunctions of the apparition - with the ice giants Uranus and Neptune - were both evening events which were favourable to Northern hemisphere observers. With a separation of just 1.2 arcminutes (0°.02), Mars' Jan 1st 2017 conjunction with Neptune was its closest with this planet since the year 1289, at which time Edward I was King of England and the Crusader state of Tripoli, Lebanon had recently fallen to the Muslim Sultan Qalawun of Egypt. This is academic, of course, since the conjunction could not have been observed by the citizens of the thirteenth century. Some 320 years would pass before the invention of the telescope (which is required to see Neptune) and a further 236 years would pass before Neptune itself was discovered!

Whilst Mars is an obvious telescopic or binocular object, eighth-magnitude Neptune was eighteen times further away than the Red Planet in January 2017 and 630 times fainter, so it had to be sought out from the smattering of background stars. Mars can easily be spotted in the dusk twilight but Neptune typically requires up to 45 minutes of additional time before the sky is dark enough for the planet to be seen through binoculars. Consequently the altitude of the two planets fell considerably by the time both of them could be seen together. When they became visible, the pair were placed 20° high in the SSW at 60° North and 43° high in the SSW at 20° North. In the Southern hemisphere, the pair were placed 38° high in the West when they became visible at 15° South and 23° high in the West at 35° South.

The Mars-Neptune conjunction of January 2017 was the Red Planet's closest passage to any planet since August 1989; its next closest passage will be with Mercury in the year 2032. Whilst this was a relatively unspectacular conjunction to observe, it was worthwhile doing so if only for its historical rarity; Mars will not come any closer to Neptune until the year 2100.

The last conjunction of the 2015-17 apparition took place on February 27th 2017, when Mars passed 0º.6 to the South of Uranus in Eastern Pisces. The circumstances applying to Neptune (above) also apply here except that, since Uranus is six times brighter than its more distant twin, it requires less time to become visible in the twilight. At higher latitudes, Uranus required an extra 20 minutes or so to become visible after Mars had first been glimpsed in the twilight. When the pair became visible in the WSW after sunset, they stood 22° high at 60° North and 31° high at 20° North. Twilight and low altitude prevented visibility of this conjunction at latitudes South of about 45° South.

The following table lists the conjunctions involving Mars which took place at solar elongations of 15º or greater. Where other planets were also in the vicinity, details are given. Note that, because some of the conjunctions occurred in twilight, the planets involved may not have appeared as bright as their listed magnitude suggests.

Although any given conjunction takes place at a particular instant in time, it is worth pointing out that, because of the planets' relatively slow daily motions, such events are interesting to observe for several days both before and after the actual conjunction date.

There are in fact two methods of defining a planetary conjunction date: one is measured in Right Ascension (i.e. perpendicular to the celestial equator) and the other is measured along the ecliptic, which is inclined at 23½° to the Earth's equatorial plane (this is due to the tilt of the Earth's axis in space). An animation showing how conjunction dates are determined by each method can be found on the Jupiter-Uranus 2010-11 triple conjunction page. Although conjunctions measured along the ecliptic can be significantly closer, the Right Ascension method is the more commonly used, and it is the one which is adopted here.

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The Southern Zodiac: Constellation Photographs

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Moon near Mars Dates, August 2015 to May 2017

The Moon is easy to find, and on one or two days in each month, it passes Mars in the sky. The following tables list the dates on which the Moon passed near the planet between August 2015 and May 2017:

The Moon moves relatively quickly against the background stars in an Eastward direction, at about its own angular width (0º.5) each hour (about 12º.2 per day). Because it is relatively close to the Earth, an effect called parallax causes it to appear in a slightly different position (against the background stars) when seen from any two locations on the globe at any given instant; the further apart the locations, the greater the Moon's apparent displacement against the background stars. Therefore, for any given date and time listed in the table, the Moon will have appeared closer to Mars when seen from some locations than others. For this reason, the dates shown in the table should be used only for general guidance.

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Credits

• The star chart was created using the commercial software MegaStar by Willmann-Bell, Inc. Star colours were based on those shown in "Patrick Moore's Colour Star Atlas" (Mitchell Beazley Publishers Ltd., London, 1973).

• The planetary conjunction dates, times and separations of the lunar conjunctions with Mars (Moon near Mars dates) and the lunar phases were obtained from the commercial software RedShift 5 by Maris Technologies Ltd using the 'Conjunctions' option of the 'Sky Diary'. Visibility durations and planet altitudes at dawn and dusk were derived using the software's 'True Sky Color' facility. The constellation boundary crossing dates were also obtained from this software.

• The information regarding the Moon, Mars and Neptune trio of January 3rd 2017 was obtained from the website The Sky and Its Phenomena by Italian amateur astronomer Pierpaolo Ricci.
• The dates of Mars' apoareion and periareion and their distances were derived from the SETI Institutes' Mars Ephemeris Generator 2.5, with supplementary data from the SkyGazer Ephemeris utility by John Biondo.
• The information regarding the origin of the star-name Torcularis Septentrionalis (Omicron Piscium) was obtained from the book "Star Names: Their Lore and Meaning" by Richard Hinckley Allen (1889), reproduced on Bill Thayer's website LacusCurtius.

• The zodiac signs are courtesy of the free graphics site .

Copyright  Martin J Powell  June 2015