|Events during May
· Mercury is at greatest elongation (27º) - 7th.
· Moon: New - 3rd, Full - 17th, Perigee - 362,135 kilometres - 15th, Apogee - 405,005 kilometres - 27th.
. The Plough: To northern observors Ursa Major, one of the best known constellations,
is almost overhead during May evenings.
Mercury reaches greatest estern elongation (27º) on the 7th May and is visible in the morning
to observors in tropical and southern latitudes. It is unsuitably placed for observors in northern latitudes this month but is the most favourable morning
apparition of 2011 for the southern hemisphere.
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.
Although the planet now rises less than two hours before the Sun, at magnitude -3.9 Venus
remains a prominent object in the east-north-eastern morning sky before sunrise for observors in the tropics and southern hemisphere.
From these latitudes on May 1st there will be a lovely grouping of the thin crescent Moon with Venus and Mercury, and Mars and Jupiter below in the pre-dawn
twilght sky. In fact, during the first two weeks of May from southern latitudes, Venus, Jupiter and Mercury form a pretty, changing grouping with Mars
located slightly below.
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, remaining at magnitude +1.2, continues to emerge in the morning sky before dawn
but is visible only in the tropics and southern hemisphere. On May 1st, Mars appears close to Jupiter in the dawn twilight sky, the two planets being just
half a degree apart with Mars to the north of Jupiter. Mars is not visible from northern latitudes during May. 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, at magnitude -2.1, becomes visible low down in the eastern sky before dawn for observors
in Europe and North America by the end of May. For those in equatorial and southern latitudes, the planet rises several hours before the Sun and is a prominent
object in the east-north-eastern early morning sky. In Pisces during May, Jupiter forms an attractive grouping
with Venus and Mercury at the beginning of the month as described above.
After spending the past six years in the southern skies, Jupiter moved north of the celestial equator on February 5th 2011 to spend the next six year
in northern skies.
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 beomes visible as soon as darkness falls and is observable for most of the night,
moving retrograde in Virgo. Saturn fades slightly from magnitude
+0.5 to +0.7 during May with the ring angle decreasing to 7.3º by the end of the month.
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: 3rd
First quarter: 10th
Full moon: 17th
Last quarter: 24th