The Planets this Month - January 2018

Mercury

Mercury reaches greatest elongation on New Years Day when it moves out to 22.7 degrees west of the Sun. The innermost planet can be seen just before sunrise during the first two weeks of the month, low down above the south-eastern horizon. During this period its brightness is fairly constant at magnitude -0.3, with its illuminated phase increasing from 62% to 85%.

Mercury passes less than a degree south of Saturn on January 13th. Two days later the thin waning crescent Moon passing 3 degrees north of Mercury.

Venus

Venus passes through superior conjunction on January 9th. It remains too close to the Sun to be safely observed throughout the month.

Earth

Earth reaches perihelion or closest point to the Sun on January 3rd at a distance of 0.983 AU or 147.1 million kilometres (91.4 million miles).

Mars

Mars is now an early morning object. Except for a few hours on the last day it spends all of the month moving south-easterly through Libra. The planet increases in brightness from magnitude +1.5 to +1.2, with its angular diameter improving slightly from 4.8 to 5.6 arc seconds as the month progresses.

Mars never strays very far away this month from much brighter Jupiter (mag. -1.9). On the morning of the 7th, the two planets are at their closest and positioned less than 0.5 degrees apart. However at magnitude +1.4, Mars is about 20 times fainter than Jupiter.

Jupiter

Jupiter is an early morning object in Libra. The giant planet rises up to 4 hours before the Sun at start of month, with the visibility period continually improving as the month progresses. On New Years Day it shines at magnitude -1.8, with an apparent diameter of 33 arc seconds, improving to magnitude -2.0 and an apparent diameter of 36 arc seconds by month's end.

Through binoculars, the planet appears as a small off-white coloured disk without detail. Also visible are the four large Galilean moons (Io, Europa, Ganymede and Callisto). Occasionally all can be seen at once, but often some are hidden from view as they pass behind, or in front of, the planet's disk.

When viewed through a telescope, Jupiter is a superb sight. Even a small 80mm (3.1 inch) refractor shows the main equatorial cloud belts with larger scopes revealing much more detail, including smaller belts, ovals, festoons, dark regions and the Great Red Spot.

As previously mentioned, on the morning of January 7th, Mars passes a fraction of a degree south of Jupiter. On January 11th, the waning crescent Moon passes 4 degrees north of Jupiter.

Jupiter and Mars during January 2018 - pdf format (credit:- freestarcharts)

Saturn

Saturn, mag. +0.6, passed superior conjunction in December and reappears in the pre dawn sky this month. During the first two weeks the ringed planet remains dangerously close to the Sun, but it climbs quickly as the month progresses and in the process becomes easier to spot.

On January 13th, Mercury (mag -0.3) passes 0.6 degrees south of Saturn. Two days later, the thin waning crescent Moon will be 3 degrees north of Saturn.

Uranus

Uranus, mag. +5.8, remains an evening object in Pisces not far from its constellation border with Aries. Uranus starts the month moving slowly retrograde before reaching its second stationary point on January 2nd. This event is widely regarded as signaling the end of the current opposition period, after which the planet again resumes direct motion. By month's end, the distant ice giant sets before midnight.

Uranus is easy to spot with binoculars and small telescopes. A small 80mm (3.1-inch) refractor at high magnifications shows a small greenish disk, 3.6 arc seconds in diameter.

On January 24th, the first quarter Moon passes 5 degrees south of Uranus.

Uranus during January 2018 - pdf format (credit:- freestarcharts)

Neptune

Neptune, mag. +7.9, is an early evening object moving direct in Aquarius. It can be seen with binoculars and small telescopes for a few hours after dark. This month offers the last realistic opportunity to catch a glimpse of the outermost planet before it reaches solar conjunction in early March.

Neptune is positioned about 30 degrees southwest of the centre of the Great Square of Pegasus and just southeast of lambda Aqr (λ Aqr - mag. +3.7). On January 20th, the waxing crescent Moon passes 1.4 degrees south of the planet.

Neptune during January 2018 - pdf format (credit:- freestarcharts)

Solar System Data Table January 2018