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 July
The Earth is at aphelion, its farthest distance from the Sun (152 million kilometres / 94.5 million miles), on the 4th July.
· A Total Eclipse of the Sun on the 22nd July.
· The Moon: Full - 7th, New - 22nd.
Anniversaries during July
· The 11th July is the 100th anniversary of the death of Simon Newcomb in 1909. Born in 1835, Newcomb was a Canadian mathematician and astronomer who made
important contributions to mathematical astronomy. He was offered the Directorship of Harvard College Observatory but declined as observation was not
his main interest. In 1877 he became Director of the Nautical Almanac Office and undertook a program of recalculating all main astronomical constants, a work
of fundamental importance.
· The 20th July is the 40th anniversary of the first men on the Moon. On the evening of July 20th 1969, Neil Armstrong and Buzz Aldrin of Apollo 11
stepped off a ladder, from the lunar module nicknamed Eagle, on to the rocky surface of the Sea of Tranquillity and said "Thatīs one small step for (a) man,
one giant leap for mankind".
· The 26th July is the 400th anniversary of the remarkable observations of the Moon by an Englishman, Thomas Harriot. Harriotīs contributions to mathematics,
navigation, algebra, optics and shipbuilding were significant achievements of the Elizabethan age. He was on one of the first expeditions to America and collaborated
with Sir Walter Ralegh. In 1609 it was from Syon House by the River Thames, where Harriot was living, that he made his first observations of the Moon with a telescope,
predating Galileoīs observations by several months.
Mercury may be seen by observors in tropical latitudes, low in the east-north-eastern sky in early morning twilight
for the first few days of July at magnitude -1.1. During the last week of the month these same observors, and those in southern latitudes, will be able to see Mercury
in the evenings low in the western sky at magnitude -0.7.
The planet remains unobservable in northerly latitudes as it passes through superior conjunction on the 14th.
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 -4.1, continues to be visible in the early morning eastern sky before sunrise.
Venus passes 3š north of the star Aldebaran in Taurus on 14th July.
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 +1.1, can be seen above the eastern horizon for several hours before dawn.
Mars passes 5š north of the star Aldebaran in Taurus on 27th July.
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 -2.8 magnitude, Jupiter continues to be a conspicuous object in the night sky,
visible for the greater part of the hours of darkness as it moves towards opposition next month. The planet
is south of the equator but visible in northern temperate latitudes in the eastern sky well before midnight.
Jupiter is moving retrograde through Capricorn and
passes just 0.6š south of Neptune around the 13th, offering a good opportunity to locate the fainter planet.
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. 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.
At magnitude +1.2 in Leo, Saturn is still visible as
an evening object in the western sky. For observors in northerly latitudes, the planet becomes increasingly difficult to observe in the long evening twilight and will
be lost to view before the end of July.
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 has an average magnitude of 7.9 which varies little with changing distance.
No longer an offical planet and never brighter than +13 magnitude, Pluto is only visible through powerful telescopes.
Full moon: 7th
Last quarter: 15th
New moon: 22nd
First quarter: 28th