Solar System Phenomena — Mercury in 2019

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The upper chart shows the path of Mercury 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. As an inferior planet, Mercury never strays far from the Sun so it always begins and ends the year near the constellation of Sagittarius, located about one quarter of the way in from the left side of the chart.

The lower charts show how the appearance of Mercury 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), the elongation from the Sun (in degrees) and the percentage of the disk which is illuminated. Like the Moon, Mercury exhibits a complete range of phases, from new to crescent to gibbous to full and back again. Because its synodic period is around four months, Mercury completes this phase cycle three times each year. Note how Mercury's magnitude varies widely, ranging (approximately) from −2.0 to +6.0 between conjunctions.

Mercury begins the year as a morning sky object. The planet reaches superior conjunction before the end of the month but there are three more morning apparitions to come. April's appearance is especially good for observers in southern latitudes whilst August and November favour the northern hemisphere. Mercury also appears in the west after sunset. The February apparition is best viewed from the north whilst October provides excellent viewing opportunities for the southern hemisphere. The June appearance is equally fine for both hemispheres. Inferior conjunction in November is particularly interesting this year as the planet is also at its ascending node, meaning it is crossing the ecliptic at the same time. This happy coincidence means planet watchers will be able to witness Mercury transit the Sun on 11 November.

01 Januaryelongation 16.4°, illuminated fraction 89.3%, magnitude −0.4, disk diameter 5.2 arc-seconds
descending node
02 JanuaryOphiuchusSagittarius
04 January2.8° south of the Moon
12 Januaryaphelion
13 Januaryplanetary conjunction: 1.7° south of Saturn
23 JanuarySagittariusCapricornus
30 Januarysuperior conjunction
01 Februaryelongation 2.5°, illuminated fraction 99.9%, magnitude −1.5, disk diameter 4.8 arc-seconds
05 Februarylunar occultation: 0.2° north of the Moon
08 FebruaryCapricornusAquarius
19 Februaryplanetary conjunction: 0.7° north of Neptune
20 Februaryascending node
22 FebruaryAquariusPisces
25 Februaryperihelion
27 Februarygreatest elongation east: 18.1°
01 Marchelongation 17.9°, illuminated fraction 39.1%, magnitude −0.1, disk diameter 7.6 arc-seconds
05 Marchstationary point: direct → retrograde
15 Marchinferior conjunction
23 MarchPiscesAquarius
24 Marchplanetary conjunction: 2.5° north of Neptune
27 Marchstationary point: retrograde → direct
30 Marchdescending node
01 Aprilelongation 24.4°, illuminated fraction 28.8%, magnitude +1.0, disk diameter 9.3 arc-seconds
02 Aprilplanetary conjunction: 0.4° north of Neptune
10 Aprilaphelion
11 Aprilgreatest elongation west: 27.7°
15 AprilAquariusPisces
22 AprilPiscesCetus
26 AprilCetusPisces
01 Mayelongation 20.6°, illuminated fraction 75.2%, magnitude −0.4, disk diameter 5.8 arc-seconds
03 May2.9° north of the Moon
08 MayPiscesAries
planetary conjunction: 1.3° south of Uranus
18 MayAriesTaurus
19 Mayascending node
21 Maysuperior conjunction
24 Mayperihelion
01 Juneelongation 12.4°, illuminated fraction 87.2%, magnitude −1.2, disk diameter 5.4 arc-seconds
05 JuneTaurusGemini
maximum declination north
18 Juneplanetary conjunction: 0.2° north of Mars
23 Junegreatest elongation east: 25.2°
24 JuneGeminiCancer
26 Junedescending node
01 Julyelongation 23.7°, illuminated fraction 26.9%, magnitude +1.1, disk diameter 9.3 arc-seconds
07 Julystationary point: direct → retrograde
08 Julyplanetary conjunction: 5.1° south of Mars
21 Julyinferior conjunction
22 JulyCancerGemini
25 Julyplanetary conjunction: 5.6° south of Venus
31 Julystationary point: retrograde → direct
01 Augustelongation 15.0°, illuminated fraction 12.6%, magnitude +2.1, disk diameter 9.6 arc-seconds
09 AugustGeminiCancer
greatest elongation west: 19.0°
15 Augustascending node
17 August1.2° south of the open star cluster M44 (known as Praesepe or the Beehive Cluster)
20 Augustperihelion
23 AugustCancerLeo
30 August1.9° south of the Moon
01 Septemberelongation 3.5°, illuminated fraction 99.4%, magnitude −1.8, disk diameter 5.0 arc-seconds
03 Septemberplanetary conjunction: 0.6° north of Mars
04 Septembersuperior conjunction
10 SeptemberLeoVirgo
13 September0.3° south of Venus
22 Septemberdescending node
29 September1.2° north of Spica
01 Octoberelongation 19.1°, illuminated fraction 85.5%, magnitude −0.2, disk diameter 5.2 arc-seconds
03 Octoberaphelion
09 OctoberVirgoLibra
20 Octobergreatest elongation east: 24.6°
30 Octoberplanetary conjunction: 2.6° south of Venus
31 Octoberstationary point: direct → retrograde
01 Novemberelongation 19.6°, illuminated fraction 29.1%, magnitude +0.6, disk diameter 8.5 arc-seconds
11 Novemberascending node
inferior conjunction: transit
16 Novemberperihelion
20 Novemberstationary point: retrograde → direct
25 November1.9° south of the Moon
28 Novembergreatest elongation west: 20.1°
01 Decemberelongation 19.8°, illuminated fraction 69.1%, magnitude −0.6, disk diameter 6.3 arc-seconds
11 DecemberLibraScorpius
14 DecemberScorpiusOphiuchus
19 Decemberdescending node
25 December1.9° south of the Moon
26 DecemberOphiuchusSagittarius
30 Decemberaphelion
31 Decembermaximum declination south

Because the orbits of the planets are tilted slightly to the plane of the ecliptic, a planet normally passes to the north or the south of the Sun at conjunction. However, if the planet is near a node (the place in the orbit where the planet crosses the ecliptic) when it reaches conjunction, the planet may appear to cross in front of or behind the disk of the Sun. This situation occurs in November when Mercury actually passes in front of the Sun from the vantage point of Earth. This phenomenon is known as a transit.

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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.