|Events during July
The Milky Way is at its very best from northern temperate latitudes this month.
See below July Snapshot
1st - MERCURY is at greatest eastern elongation (26º).
4th - EARTH is at aphelion, its farthest distance from the Sun (152 million kilometres / 94.5 million miles).
10th/11th - JUPITER lies very close to omega-2 (magnitude +4.9) in Taurus.
Through binoculars or a small telescope it will look as though Jupiter´s 4 bright moons have increased to 5!
15th - JUPITER is occulted by the Moon as seen from Europe. This rare event commences
at 03.55h and ends at 04.10h.
28th - MERCURY is at inferior conjunction.
MOON: Full - 3rd, New - 19th, Perigee - 362,360 kilometres - 1st and 367,315 kilometres - 29th,
Apogee - 404,780 kilometres - 13th.
1st July - the almost full Moon lies near Antares (a red supergiant in Scorpio).
15th July - in the early hours the crescent Moon ocults the giant planet of Jupiter with Venus set picturesquely below.
16th July - before dawn Venus, and Jupiter higher in the sky, are to the right of the crescent Moon.
24th July - the Moon lies below Mars.
25th July - the Moon is near Spica the brightest star in Virgo, with Saturn above.
28th July - the Moon is above Antares.
Following the Summer Solstice in June, slowly at first, the days are getting shorter. For observers in the southern hemisphere, the days are lengthening.
This July is a month for stars rather than planets. Gaze at the Summer Triangle as it soars overhead, with Vega, Deneb and Altair each
the brightest star in their own constellation - Vega in Lyra
, Deneb in
and Altair in Aquila
. Vega is the western point
and appears the brightest of the three stars. Deneb, to the east of Vega, appears the dimmest. Altair, below in the south, is the most distant point of this triad.
The Milky Way is at its very best from northern temperate latitudes this month.
The Summer Triangle is an unofficial star group or asterism that links the three constellations and lies over the Milky Way which now sweeps
from Perseus in the northeast, through Cassiopeia,
passing close to the zenith, through Cygnus and Aquila sweeping down to the far-southern constellations of
Sagittarius and Scorpio which you can catch
in the southwest.
If you´re lucky enough to be under a dark starry sky on a moonless night, you´ll see the Milky Way passing between the Summer Triangle stars
Vega and Altair, while Deneb lies in the middle of this river of stars. Although every star that you see with the unaided eye is a member of
our Milky Way galaxy, the term Milky Way is usually used to refer to the cross-sectional view of the galactic disk, where innumerable far-off
suns congregate into a cloudy trail of stars. Once you can spot the Summer Triangle, you can always locate the Milky Way on a clear, dark night.
How about making the most of a dark summer night to explore this band of stars in this starlit boulevard abounding with celestial delights? Use binoculars
to reel in the gossamer beauty of it all, the haunting nebulae and star clusters of a midsummer night´s dream!
Mercury is at greatest eastern elongation
on July 1st. The planet is
still on view at dusk in the north-western twilight sky for observors in the tropics and southern hemisphere during the first half of July. For observors in northerly
latitudes, the planet is unlikely to be seen low down in the bright evening twilight sky.
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.
Venus, at magnitude -4.4, rises over two hours before the Sun at the beginning of July from equatorial
and more southerly latitudes from where the planet makes a lovely pairing with the fainter Jupiter in the dawn twilight sky. Venus is rather low in the dawn sky for
observors further north but this improves as July progresses and Jupiter draws rapidly away from the Sun so that by the end of the month the planet rises three hours
before the Sun from northerly latitudes. The phase of Venus will increase from 17% to 41% by the end of July.
On the 8th June 2004 and 5th/6th June 2012, 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. Prior to that, the last two transits of Venus were in 1874 and 1882. Transits of Venus won't occur again until 2117
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.
Mars is visible as soon as darkness falls and sets before 1am. The planet is moving
directly in Virgo some way to the west of Saturn. Mars
fades from +0.9 to +1.1 magnitude during the month.
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 is a conspicuous object in the early morning sky, increasing in brightness slightly from
-2.0 to -2.1 during July, and moving directly in Taurus. From
northern temperate latitudes, Jupiter begins July low down just north of east in the dawn twilight with the much brighter Venus below it. On the morning of July 15th,
the waning crescent Moon lies very close to Jupiter with Venus below. By the end of July, Jupiter will rise before midnight.
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 Jupiter´s 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 is visible as an early evening object in Virgo
throughout July, setting before midnight. Its brightness decreases from magnitude +0.7 to +0.9 during 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 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: 3rd
Last quarter: 11th
New moon: 19th
First quarter: 26th