|Events during January
· Earth is at perihelion (147 million kilometres - its closest to the Sun) - 3rd.
· Partial Eclipse of the Sun occuring at sunrise, visible across Europe, Africa and central Asia - 4th.
· Venus at greatest western elongation (47º) - 8th.
· Mercury at greatest western elongation (23º) - 9th.
· Moon: New - 4th, Full - 19th, Apogee - 404,980 kilometres - 10th, Perigee - 362,790 kilometres - 22nd.
· The Quadrantids meteor shower is visible from the 1st to the 6th January, at maximum on the 4th. Visibility in 2011 is perfect with a New
Moon on the same day as maximum meteors. The average hourly rate can range from 10 to 120, with the radiant low in the north during evening time.
Mercury passed through inferior conjunction
on December 20th 2010 and, having moved rapidly west of the Sun, reaches greatest western elongation
on the 9th January. For a few day before and after this date Mercury is visible from northern temperate latitudes low above the south-eastern horizon at the
beginning of morning twilight. For observors in equatorial and southern latitudes the length of visibility extends to the end of the month with the planet higher
above the east-south-eastern horizon. Mercury´s magnitude increases from +0.2 to -0.3 during January.
The best times to observe Mercury in the northen hemisphere are when it is an evening star in the spring and a morning star in the autumn. In midsummer
the lighter skies make visibility difficult near the horizon.
Venus is a brilliant morning object in the south-eastern sky before dawn, reaching
greatest western elongation
(47º) on January 8th. In northern temperate latitudes Venus rises four hours
before the Sun at the beginning of January. From the southern hemisphere the planet rises just three hours before the Sun.
The planet is in Libra fading from -4.5 to -4.3 magnitude during January. During the month the
phase of the planet increases from 47% to 60% (from less than half phase to gibbous).
On January 30th the waning crescent Moon will pass close to Venus making a pretty spectacle in the dawn twilight sky.
On the 8th June 2004, Venus was at inferior conjunction
and transited the sun. Transits of Venus are rare, taking place at greater
than 100 year intervals and usually in pairs. The last two transits of Venus were in 1874 and 1882. June's transit
began at 7.20h and lasted 6 hours until 13.20h, the total event visible from Europe as a small black disc crossing
the lower part of the Sun from left to right. The next transit will be in late June 2012. After that, transits of Venus
won't occur again until 2117 and 2125.
Before and after inferior conjuction, when Venus is
the closest it comes to the Earth, are the times at which the planet is most brilliant and can be seen setting or rising
4 hours after or before the Sun. The dates of the next two inferior conjunctions are October 28th 2010 and October 26th 2018.
Mars will pass through superior conjunction
on the far side of the Sun in February so is too close to the Sun to be visible during January. There will be no opposition of Mars in 2011.
At opposition on the 28th August 2003, Mars was only 56 million kilometres from the Earth. It showed a
disc of 25.1 seconds of arc across which is almost as large as it can ever appear. Mars started 2003 at 310 million kilometres from
the earth at 4.5 seconds of arc and 1.6 magnitude. By opposition it brightened 50 times to reach -2.9 magnitude but faded to 0
magnitude by December. Even to the naked eye Mars was a striking object in the summer and autumn sky, easily identifiable by its
reddish hue in an area of sky poor in bright stars. Mars will not be as close again until 2018.
These favourable oppositions occur every 15 or 17 years but other oppositions occur at average intervals of 2 years 2 months during
which time the planet makes a complete circle of the Earth. In general Mars is observable every other year, being too close to the sun for favourable conditions
during other times. Brightness at opposition varies from -1.0 to -2.9 magnitude, and when furthest from the earth it fades to 1.7 magnitude. The planet can be
identified by its orange-red colour.
As in 2003, Mars comes nearest to the Earth at oppositions at the end of August. At these times it can be brighter than Jupiter,
although low in the sky in Aquarius for northern observors. In the northern hemisphere, the planet may be better seen at oppostions during autumn and winter months
when it is higher in the sky.
Jupiter remains a splendid early evening object visible in the south-western sky after dark
and setting an hour before midnight. The planet is moving direct in Pisces, fading from -2.3 to -2.2 during January.
The four Galilean moons can still easily be seen through a small telescope or good pair of binoculars.
On January 2nd Jupiter passes about 0.5º south of Uranus (magnitude +5.9) and is a useful guide to locating the fainter planet.
Varying from 603 (at its closest) to 770 million kilometres from the sun, the difference in brightness between opposition and conjunction varies less than
with Mars, from about -2.9 to -1.8 magnitude. Always a bright planet, Jupiter comes to opposition a month later each year, moving approximately from one zodiacal
constellation to the next.
The 4 largest moons of Jupiter are easily visible through a small telescope, ranging from 4.6 to 5.6 in magnitude. The innermost, Io, takes 1.8 days
to orbit the planet making its motion easily detectable within a few minutes.
Saturn rises shortly before midnight and brightens from +0.8 to +0.6 during January. The planet is in
Virgo where, after reaching the first stationary point on January 27th, it follows a
Saturn´s rings are now opening again and are displayed at an angle of 10.1º viewed from Earth, making the planet a glorious sight once more even in a small telescope
Saturn moves more slowly than Jupiter and can remain in the same constellation for several years. The brightness of the planet depends on the
aspect of its rings, as well as its distance from Earth and the Sun.
The planet crossed the equator into the northern hemisphere in 1996 where it remained until 2010 with the southern side of the ring system
facing the earth. Because of its distance, its brightness varies little between opposition and conjunction but is affected by the huge ring system. Seen edge on the
rings contribute little or no light.
Every 15 years the plane of Saturn's rings passes through the sun, illuminating first the north and then the south side. For a few days the
rings are edge on to the sun. About the same time the Earth passes through the ring plane and, depending on the Earth's position, this may happen just once or 3 times.
During 1995/96 there was a triple crossing and the next will be 2038/39. The last single crossing was in 2009 and the next will be in 2025.
Saturn's largest moon, Titan, is visible in small telescopes orbiting outside of the ring system.
Brightness varies slightly, reaching a maximum of +5.6 magnitude at opposition. This is bright
enough to see with the naked eye but identifying it against the stars is difficult. At closest approach, Uranus is 2,856 million kilometres (1,775 million miles)
Neptune has an average magnitude of 7.9 which varies little with changing distance. At its closest,
Neptune is 4,341 million kilometres (2,697 million miles) from Earth.
No longer an offical planet and never brighter than +13 magnitude, Pluto is only visible through powerful telescopes.
New moon: 4th
First quarter: 12th
Full moon: 19th
Last quarter: 26th