|Events during August
· The Perseids meteor shower is visible from 23rd July until 20th August, at maximum on the 12th August. Visibility in 2010
is excellent with a New Moon on the 10th. An average hourly rate of 75 is expected.
· Mercury at greatest eastern elongation (27º) - 7th.
· Venus at greatest eastern elongation (46º) - 20th.
· Neptune at opposition in Capricorn - 20th.
· The Moon: New - 10th, Full - 24th. Perigee (357,86 kilometres) - 10th, Apogee (406,390 kilometres) - 25th.
Mercury reaches its greatest eastern elongation
of 27º on 7th August. For observors in tropical and southern latitudes, the planet is visible as an evening object until the last week of August. For observors
in the southern hemisphere this is the most favourable evening apparition of 2010.
During August, Mercury fades from +0.2 to +1.5 magnitude.
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 continues to be visible in the western sky in the early evening after sunset, although
for observors in northern temperate latitudes the planet is too low in the twilight by mid-August. From the tropics and the southern hemisphere, Venus is a magnificent
object brightening from -4.2 to -4.4 magnitude during August.
Venus moves into Virgo at the beginning of the month. On the 7th, southern hemisphere observors will see a close
grouping of Venus, Mars and Saturn with Mercury below. Venus passes 2.7º south of Saturn on 8th August and the crescent Moon joins the party on the 12th and 13th August.
Venus reaches greatest eastern elongation of 46º on 20th August and on the same day passes 2.0º south of Mars.
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.
At +1.5 magnitude, Mars continues to be visible in the western evening sky as an early
evening object, observable in the tropics and the southern hemisphere. Mars is in Virgo
and not far from Venus
during the second half of August.
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 brightens from -2.7 to -2.9 during August and will be in
opposition in September. The planet is in Pisces,
moving retrograde, rising soon after sunset and visible throughout the hours of darkness.
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 is another planet in Virgo this month. No
longer visible in northern latitudes, but during early August it can be glimpsed low in the western sky after sunset by observors in the tropics and southern hemisphere.
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 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.
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 at opposition
on 20th August
at +7.8 magnitude.
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.
Last quarter: 3rd
New moon: 10th
First quarter: 16th
Full moon: 24th