|Events during April
|15th - SATURN at opposition in
18th - MERCURY at greatest western elongation.
VENUS and SATURN are the major players of April this year - see details below.
MOON: Full - 6th, New - 21st, Perigee - 358,315 kilometres - 7th,
Apogee - 406,420 kilometres - 22nd.
3rd - Moon below Mars with Regulus, the brightest star in Leo, to the right of Mars.
6th/7th - Saturn and Spica (the brightest star in Virgo) to the left of the Full Moon.
10th - The waning Moon will lie above Antares (a red supergiant in Scorpio) in the early hours.
22nd - the thinnest of crescent Moons lies above Jupiter just after sunset.
24th - The Moon is near Venus in the evening sky.
Meteor Showers during April
The LYRIDS meteor shower from April 19th to 25th, consisting of particles from Comet Thatcher,
reaches max-imum meteor rate between 21st and 22nd.
The April Lyrids, by perspective, appear to emanate from the constellation of Lyra. With the peak occurring in the early morning hours as the radiant climbs,
and with no interference from moonlight this year, 2012 is expected to be a bumper year for observation of this shower.
The best way to observe meteors is to lie outdoors in a reclining chair or sun-lounger. Try to take in as much of the sky as possible. When you see a meteor
mentally trace it backwards until you arrive at the radiant point.
Mercury reaches greatest western elongation
(28š) on 18th April and is visible in the morning for observors in tropical and southern latitudes. For the southern hemisphere this is the most favourable
morning apparition of the year.
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.
Following greatest eastern elongation on 27th March,
Venus remains a spectacularly brilliant object in the evening sky. Whilst brightening slightly from -4.4 to -4.5 magnitude during April, the
phase decreases from 48% to 27%, the change in shape being observable through a small telescope. From northern temperate
latitudes the planet sets more than four and a half hours after the Sun. From latitude 35šS this length of time is reduced to just two hours.
Venus is moving against the constellation of Taurus and appears very close to
The Pleiades (Seven Sisters) on April 3rd creating an interesting photographic opportunity.
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. 2004's transit lasted 6 hours, 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 on 5th 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.
Following opposition during March, Mars fades from
-0.7 to 0.0 magnitude during April. The planet begins the month moving retrograde in
Leo and reaches its second stationary point on April 14th, after which it resumes direct motion. The apparent
diameter of the planetīs disk drops below 10 arc seconds by the end of April.
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 -2.0, is moving towards conjunction
with the Sun in May and will therefore be lost in the glare of evening twilight by the end of April. Earlier in the month Jupiter may be spotted low in the twilight sky just
north of west about half-an-hour after sunset. At this same time on April 22nd, Jupiter will lie close to the very thin crescent Moon about 6š high in the
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 years
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 of Jupiterīs 60+ moons are easily visible through binoculars or 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, magnitude +0.3, is at opposition in
Virgo on April 15th. The planet becomes visible in the east-south-eastern sky as soon as darkness falls and is observable all night
through. With the rings displayed at 13.7š, as viewed from Earth, Saturn is a beautiful sight in even 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 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 only slightly, reaching a maximum of +5.6 magnitude at opposition. Although this is
bright enough to see with the naked eye, identifying it against the stars can be 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.
Full moon: 6th
Last quarter: 13th
New moon: 21st
First quarter: 29th