|Special Events in July
The Earth is at aphelion (furthest from the sun – 152 million kilometres) on the 5th, Mercury is at
greatest eastern elongation on the 9th, Mars is at perihelion on the 17th, there is a full moon on the 21st, Mercury is
stationary on the 22nd and Saturn is conjunct with the sun on the 23rd.
||Mercury fades from 0.0 to 0.5 magnitude by the end of July. On the 8th July
Mercury will be just below Venus and the crescent moon will be just above Venus. Mercury is at greatest eastern elongation
(26º) on the 9th and is stationary on the 22nd.
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.
||Venus remains at –3.9 magnitude but, setting just one hour after the sun by
the end of July, is not easy to observe. As above, Mercury is close from the 6th to the 8th and the crescent moon is above
on the 8th.
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 moves from Pisces into Aries brightening from 0.0 to –0.4 magnitude and
rising by 0.30h by the end of July. On the 17th Mars is at perihelion (the point in its orbit when it is nearest to the sun).
The moon is close to Mars on the 27th.
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 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 in Virgo, paling further to -1.9 magnitude, setting at about 24.00h
by the end of the month. The moon is below on the 13th.
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 conjunction with the sun on the 23rd July and is not observable
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 rising by 23.00h by the end of July with the moon closeby
on the 23rd.
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 rising at sunset by the end of July. The moon is
closeby on the 21st.
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.|
||New moon: 6th at 12.00h
First quarter: 14th at 15.00h
Full moon: 21st at 11.00h
Last quarter: 28th at 03.00h