|Events during July
|1st - Partial Solar Eclipse - Occurs just one lunar month after the June 1st eclipse, therefore two partial solar eclipses
(and one total lunar eclipse) take place in one node - a relatively rare event. As often in these circumstances, an eclipse visible from the far north
of Earth is followed by one visible from the far south. Thus the 1st July eclipse is only visible in Antarctic waters.
4th - Earth is at aphelion, its farthest distance from the Sun (152 million kilometres / 94.5 million miles).
20th - Mercury is at greatest eastern elongation (27º).
Following the Summer Solstice on June 21st, slowly at first, the days are getting shorter. For observers in the southern hemisphere, the days are lengthening.
MOON: New - 1st and 30th, Full - 15th, Perigee - 369,570 kilometres - 7th, Apogee - 404,355 kilometres - 21st.
This month is unusual for having two New Moons. A second Full Moon in a month is called a Blue Moon but there is no special term for a second New Moon.
Mercury reaches greatest eastern elongation (27º) on 20th July and is visible in the evening
throughout the month for observors in equatorial and southern latitudes from where it is the most favourable evening 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.
At magnitude -3.9, Venus is at superior conjunction
in August and, as its elongation
from the Sun decreases, it is increasingly difficult to see in the dawn twilight sky.
The planet is too low from northern temperate latitudes throughout July but observors in equatorial and southern latitudes may glimpse it low in the east-north-eastern sky for
the first few days of the month before losing it in the brightening sky.
Observors in northern latitudes will have to wait until December for a true Venusian (evening) spectacle.
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, at magnitude +1.4, is an early morning object, but still rather low in the east-north-eastern sky.
Mars moves fairly rapidly against the constellation of Taurus
during July. At the beginning of the month it is about
midway between Pleiades and Aldebaran and by the end of July is approaching the border with neighbouring Gemini
There is 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 continues to be a conspicuous early morning object, moving with direct motion against
the constellation of Aries. By the end of July, Jupiter rises before midnight with brightness increasing
slightly from -2.2 to -2.4 magnitude.
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 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, at magnitude +0.9, beomes visible as soon as darkness falls and is observable, in the
constellation of Virgo, until setting before midnight. The angle at which the rings are displayed begins to
increase slightly, reaching 8º 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.
Uranus is in Pisces all month, visible before dawn.
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 is a morning object in Aquarius
, visible in binoculars or a small telescope.
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: 1st
First quarter: 8th
Full moon: 15th
Last quarter: 23rd
New moon: 30th