During July the full moon is on the 2nd and the 31st, the Earth is at aphelion (greatest distance
from the sun - 152 million kilometres) on the 5th, Saturn is in conjunction with the sun on the 8th and Venus is at
greatest brilliancy on the 15th.
||During the first half of July Mercury is visible at -1.0 magnitude low in the northwest sky
after sunset. The moon is nearby on the 19th and Mars on the 10th. As July progresses Mercury will be too low and faint to
The best times to observe Mercury 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.
||2004 is an exceptional year for observing Venus and during July the planet is a brilliant -4.5
magnitude in Taurus with greatest brilliancy on the 15th. By the end of July Venus rises 3 hours before the sun with
the moon to the north on the 14th. Venus will remain as a brilliant morning object in the northeast sky throughout the remainder of 2004.
On the 8th June, 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 has faded from its brilliant August 2003 display to a faint 1.8 magnitude. During late July
the planet moves from Cancer into Leo and is in bright twilight moving closer towards the sun until conjunction in September.
It will not be visible against a dark sky until late October.
At opposition on the 28th August last year, 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 for another 15 years.
These favourable oppositions occur every 15 years but other oppositions occur at average intervals of 2 years 2 months. 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.
||Jupiter is at -1.8 magnitude in Leo setting by 3 hours after the sun at the beginning of July
but in twilight by the end of the month. The moon is closeby on the 20th and 21st.
Being 770 million kilometres from the sun, the difference in brightness between opposition and conjunction varies less than with Mars, from about -2.8 to -1.8 magnitude.
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 is in Gemini throughout 2004. Conjuct with the sun on the 8th July, the planet will be visible
again in August in the morning sky.
Saturn crossed the equator into the northern hemisphere in 1996 where it will remain 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 next single crossings will be in 2009 and 2025.
Saturn's largest moon, Titan, is visible in small telescopes orbiting outside of the ring system.
||Uranus is in Aquarius throughout 2004 rising after sunset by the end of July. The moon is
closeby on the 6th.
Brightness varies slightly reaching 5.6 magnitude at opposition. This is bright enough to see with the naked eye but identifying it against the stars is difficult.
||Neptune is in Capricorn throughout 2004. At 8.0 magnitude, it rises at sunset by the end
of July with the moon nearby on the 4th.
Neptune has an average magnitude of 7.9 which varies little with changing distance.
||Never brighter than 13 magnitude, Pluto is only visible through powerful telescopes and we will therefore not be reporting on its position in the sky.|
||Full moon: 2nd at 11.00h
Last quarter: 9th at 8.00h
New moon: 17th at 11.00h
First quarter: 25th at 4.00h
Full moon: 31st at 11.00h