IYA2009 - 2009 IS THE INTERNATIONAL YEAR OF ASTRONOMY
Commemorating glorious events particularly the 400th anniversary of Galileo’s invention of the telescope
Slogan - The Universe, Yours to Discover
|Events during August
The Perseids meteor shower is visible from 23rd July until 20th August, at maximum on the 12th August. Visibility in 2009 is slightly unfavourable
due to the Moon becoming full on the 6th, the light from which interferes with the number of meteors that can be seen. An average hourly rate of 75 is expected.
The meteors can be seen streaking out from the direction of the radiant point between the constellations of Perseus and Cassiopeia. The best way to observe them is
to lie outdoors in a reclining chair or sun-lounger, facing north. You can carry on watching,
as Perseus climbs higher in the sky, until dawn when sunlight will prevent observation. The hours preceding dawn are best to watch for meteors, when the speed of
the Earthīs rotation combines with that of its orbital motion, ploughing through the dust trail at maximum speed. Because meteor showers cover such a broad area
of the sky, they are best viewed with the naked eye as binoculars and telescopes restrict the field of vision.
The source of the Perseids shower is Comet Swift-Tuttle. Although nowhere near Earth, the comet's wide tail intersects Earth's orbit and we pass through it
every year in July and August. Sometimes called shooting stars, meteors can vary in size from a grain of sand, through pea-size producing a more spectacular display,
to rare stunning fireballs the size of an apple. Upon collision with Earthīs atmosphere, about 95 kilometres above Earthīs surface, they begin to glow white hot and
we witness a streak of light as they burn up. The shower is most intense from the 11th to the 14th August when Earth is in the dustiest part of the tail.
· The Moon: Full - 6th, New - 20th.
· A Penumbral Eclipse of the Moon on the 6th August.
Anniversaries during August
· The 13th August is the anniversary of the discovery of the large main belt asteroid no 7, Iris, by British astronomer John Russell Hind in 1847. Hind spent most
of his career at the Royal Greenwich Observatory. Iris was his first asteroid discovery, followed by nine others the last of which was no 30 Urania in July 1854. Hind
was awarded the Gold Medal of the Royal Astronomical Society in 1853 and now has an asteroid, no 1897, named after him.
Mercury reaches its greatest eastern elongation of 27š on 24th August and fades from -0.5 to +0.5
magnitude during he month. For observors in tropical and southern latitudes, Mercury is visible as an evening object throughout August.
Mercury is not suitably placed for observation from northen latitudes.
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, still at a magnificent magnitude -4.0, continues to be visible in the early morning
east-north-eastern sky before sunrise.
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 +1.0, continues to be visible as a morning object and during August
is rising above the east-north-eastern horizon five hours before sunrise. Mars is in Taurus
, northeast of
Aldebaran, at the beginning of August and enters Gemini
before the end of 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.
At -2.9 magnitude and in opposition on the 14th,
Jupiter in Capricorn is now at its brightest and can be observed throughout the night from anywhere on Earth.
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.
Remaining at magnitude +1.2 in Leo and moving into
Virgo by the end of August, Saturn is an evening object for observors in tropical and southern latitudes.
On 10th August 2009 the Sun passed through Saturnīs ring plane from south to north. As Earth remains south of this plane until September, the Sun and the Earth are on
opposite sides of the ring plane during this time making the rings invisible from Earth.
Saturnīs rings continue to close with the south pole presented towards Earth and the far side of the rings no longer appearing clear of the planetīs body. This year the
Earth will pass through the ring plane making the rings invisible for a short while. This will be the first time since 1997 that the planetīs magnitude has faded to
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 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 at opposition on the 17th in
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: 6th
Last quarter: 13th
New moon: 20th
First quarter: 27th