As seen from Earth, the motion of all planets is eastwards taken over the whole year. As Earth is also
moving, and more quickly than the outer planets, it overtakes them around the time of opposition. At this time the outer
planets appear to move backwards against the stars.
The term used to descibe forward easterly direction is direct motion and backwards motion is called retrograde.
The point at which the motion changes from direct to retrograde, or back again, is when a planet is said to be stationary. The position
at which a planet becomes retrograde prior to opposition is the 1st stationary point and that a which it resumes direct motion following
opposition is the 2nd stationary point.
In the diagram the direct motion to the east is shown at positions 1,2 and 3, backward motion to
the west at 4 and 5, and direct motion to the east again at positions 6 and 7.
Oppositions (position 4) occur when an outer planet is in the opposite side of the sky from the
Sun as viewed from the Earth. At opposition the planets are at their brightest. Mercury and Venus can never be at opposition since they are inside
of the Earth's orbit and, therefore, remain relatively close to the Sun. The brightest times for Mercury and Venus are close to greatest
elongations.
The other side of the cycle from oppositions are conjunctions when, as viewed from Earth, a planet
is in line with the Sun whose glare is too bright for the planet to be visible in the night sky.
Venus and Mercury, as inner planets, move very quickly against the constellations.
They have no stationary or retrograde motion and are always seen moving easterly against the stars.
During 2010:
Mercury, the Solar System´s smallest planet, moves from the morning sky to evening sky
several times a year. As it never strays far from the Sun, it can be hard to find in the Sun´s glare.
From the northern hemisphere, the most favourable evening appearance of 2010 is during April and the most favourable morning
apparition is during September.
| 2010 |
Mercury Event |
| January 04 |
Inferior Conjunction |
| January 27 |
Greatest Elongation West - 25º - mag -0.1 |
| March 14 |
Superior Conjunction |
| April 08 |
Greatest Elongation East - 19º - mag -1.4 |
| April 28 |
Inferior Conjunction |
| May 26 |
Greatest Elongation West - 25º - mag -1.0 |
| June 28 |
Superior Conjunction |
| August 07 |
Greatest Elongation East - 27º - mag +0.2 |
| September 03 |
Inferior Conjunction |
| September 19 |
Greatest Elongation West - 18º - mag -1.1 |
| October 17 |
Superior Conjunction |
| December 01 |
Greatest Elongation East - 21.5º - mag -0.4 |
| December 20 |
Inferior Conjunction |
Venus, the dazzling morning or evening star, outshines all the other stars and planets
in the night sky. However, Venus commences 2010 passing through Superior Conjunction on January 11th and too close to the Sun to be visible.
Venus draws away from the Sun to become an evening object from February to late October and Inferior Conjunction. After this the planet reappears as a
spectacular early morning object until the end of the year.
| 2010 |
Venus Event |
| January 11 |
Superior Conjunction |
| August 20 |
Greatest Elongation East - 46º - mag -4.4 |
| September 23 |
Greatest Brilliancy - mag -4.6 |
| October 29 |
Inferior Conjunction - mag -4.6 |
| December 04 |
Greatest Brilliancy - mag -4.7 |
Mars begins 2010 moving westwards retrograde in the constellation of Leo, then moves into Cancer. The planet
is closest to the Earth on 27th January, at 99.3 million kilometres (61.7 million miles) and at opposition on the 29th January. At this time
Mars´ north pole is tilted towards the Earth, it has a magnitude of -1.3, an apparent disk diameter of 14.1 seconds of an arc, rises during
early evening and is visible all night long.
During February Mars continues its retrograde motion with a magnitude fading from -1.3 to -0.6 during the month as its distance from Earth increases.
It can be seen in the eastern sky as soon as darkness falls and is visible for most of the night.
In March Mars is high in the southern sky throughout the evening with a magnitude further decreasing from -0.6 to +0.2. The planet reaches its
2nd stationary point on the 11th after which it resumes a direct easterly motion. On March 31st Mars is at aphelion, its greatest distance from
the Sun - it will be 249.2 million kilometres (154.8 million miles) from the Sun and 150.5 kilometres (93.5 million miles) from Earth.
During April and May Mars remains in Cancer, in the southern sky after dark, fading to +0.7 magnitude in April and +1.0 by the end of May.
By June Mars has moved back into Leo, is visible in the evening sky but sets after midnight and fades to +1.3 magnitude. By late July the
planet moves into Virgo, sets before midnight and has faded to +1.4 magnitude. On 31st July Mars passes 1.8º south of Saturn.
By August, at magnitude +1.5, Mars is visible in the early evening western sky but only for observors in the tropics and southern hemisphere.
For the remainder of the year Mars is not visible in the northern hemisphere. It moves into Libra during September and is still visible in
southern latitudes until October. By November Mars is too close to the Sun for anyone to observe, leading up to conjunction in February 2011.
| 2010 |
Mars Event |
| January 29 |
Opposition - Cancer - mag -1.3 |
| March 11 |
2nd Stationary Point - Cancer - mag -0.6 |
Jupiter begins 2010 at -2.1 magnitude, visible in the early evening western sky. During early January
the planet moves from Capricorn into Aquarius.
In February Jupiter has a 0.2º close conjunction with Venus on the 16th/17th. Venus is six times brighter than Jupiter but both objects are
low in the twilight sky and difficult to spot. Jupiter is in conjunction with the Sun on the 28th February and so may not be observed until
the last week of March in the southern hemisphere, low in the eastern sky before dawn.
In May Jupiter, at -2.2 magnitude, moves from Aquarius into Pisces and becomes visible low in the south-eastern sky before dawn in Europe
and north America. In equatorial and southern latitudes, the planet rises several hours before the Sun and dominates the eastern morning sky.
In June brightness increases to -2.5 magnitude and, on the 8th, it passes just 0.4º south of the planet Uranus (at magnitude +5.9).
In July, on the 24th, Jupiter reaches its first stationary point after which it begins a retrograde (westerly) motion.
From August through opposition on 21st September and into October Jupiter, remaining in Pisces at a brilliant -2.9 magnitude, is visible
throughout the hours of darkness.
In November Jupiter, in Aquarius, reaches its 2nd stationary point on the 19th and then resumes direct motion. It is visible from darkness
and sets in the early morning. As its distance from Earth increases, magnitude fades to -2.5 by the end of November.
Jupiter sees the year out, still as a bright -2.3 magnitude early evening object, setting about midnight. Its direct motion carries the
planet back into Pisces during December.
| 2010 |
Jupiter Event |
| February 28 |
Conjunction - Aquarius - mag -2.0 |
| July 24 |
1st Stationary Point - Pisces - mag -2.7 |
| September 21 |
Opposition - Pisces - mag -2.9 |
| November 19 |
2nd Stationary Point - Aquarius - mag -2.7 |
Saturn remains in the constellation of Virgo throughout 2010, seeing the year in at +0.8 magnitude. After its 1st
stationary point on January 14th, Saturn becomes retrograde through opposition in March until following the 2nd stationary point at the end of May when
it recommences an easterly motion. Following the ring-plane crossing in September 2009, Saturn´s rings have been gradually opening and are at an angle
of 4.8º at the beginning of January making them discernible in a small telescope.
In February the rings have closed slightly to 4º and Saturn´s magnitude is +0.7. The planet can be seen rising in the eastern sky in the late evening.
During March Saturn is at +0.6 magnitude, rises in early evening and is visible throughout the night. The width of the rings has further decreased to
3º. On March 22nd Saturn is at opposition and has a distance of 1,272 million kilometres (790 million miles) from Earth.
During April Saturn is still visible throughout the night with a magnitude fading slightly to +0.8. The angle of the rings decreases to just 2º by the
end of April.
In May Saturn is still visible as an evening object but sets in the early hours of morning. Magnitude decreases to +1.0 and the ring angle, at only 1.7º,
reaches its minimum for the year. On the 31st May Saturn reaches its 2nd stationary point and resumes direct motion.
In June Saturn continues to be an evening object, setting after midnight by the end of the month. Its magnitude decreases to +1.1 and the ring angle
opens a tiny bit to 2º.
In July magnitude remains at +1.1 and the planet sets before midnight. By August, at magnitude +1.0, the planet is only visible in the tropics and
southern hemisphere, low in the western sky after sunset. By september Saturn is approaching conjunction with the Sun at the beginning of October and is
too close to our star to be visible until November.
In November Saturn becomes visible low in the eastern sky before dawn at magnitude +0.9, increasing to +0.8 in December.
Saturn´s moons tend to be hidden in the glare of the rings when they are wide open and, with the exception of 8th-magnitude Titan, all of Saturn's moons are
fairly faint and easily confused with background stars. Moreover, the innermost moons, with orbital periods of just one or two day days, swap positions at a
furious rate making it difficult to identify them. From Earth-based telescopes, ring plane crossings have been the best times to view Saturn´s extensive family
of moons and to discover new moons but during the 2009 occasion the Sun was only 11º east which was too close for good observation.
| 2010 |
Saturn Event |
| January 14 |
1st Stationary Point - Virgo - mag +0.8 |
| March 22 |
Opposition - Virgo - mag +0.6 |
| May 31 |
2nd Stationary Point - Virgo - mag +1.0 |
| October 01 |
Conjunction - Virgo |
| 2010 |
Uranus Event |
| March 17 |
Conjunction |
| September 22 |
Opposition - Pisces - mag +5.7 |
| 2010 |
Neptune Event |
| February 14 |
Conjunction |
| August 20 |
Opposition - Capricorn - mag +7.8 |