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Events during June
· For observers in the northern hemisphere, the sun lies high in the sky during the day and not far below the
horizon at night, giving long twilight hours and short nights. The Summer Solstice, when the Sun reaches its most northerly point over the
Tropic of Cancer, is on the 21st. After this, slowly at first, the days start getting shorter. For observers in the southern hemisphere,
the days will start to get longer.
· The Moon: Full - 7th, New - 22nd. On June 19th, as a thin waning crescent, the Moon is just 6-7 degrees above Venus and Mars in
the pre-dawn sky.
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Mercury
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Mercury becomes visible in the eastern morning sky after the first week of June for observors in
tropical and southern latitudes. During the period of visibility, its magnitude brightens from +1.0 to -0.9. For northerly observors, the long period of twilight
makes the planet unsuitably placed for observation throughout the month.
Mercury reaches its greatest western elongation of 23š on 13th June.
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.
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Venus
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Venus, at magnitude -4.2, continues to be visible in the early morning eastern sky before sunrise. On 5th June it attains
greatest western elongation of 46š from the Sun.
Venus passes 2š south of Mars on 21st June.
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.
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Mars
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Mars, already visible to observors in tropical and southern latitudes, becomes visible to observors in northern
temperate latitudes during the second half of June. For northern obsrvors it will be a difficult object to detect, being very low above the eastern sky for a short
while about two hours before dawn at magnitude +1.1.
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 oppositions during autumn and winter months
when it is higher in the sky.
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Jupiter
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At -2.6 magnitude Jupiter continues to be a conspicuous object in the night sky, crossing the meridian around midnight by the
middle of June. On 15th June, Jupiter reaches its first stationary point on the border of
Aquarius and Capricorn, after which it follows a
retrograde motion.
Two of Jupiterīs moons, Io and Ganymede, cast shadows simultaneously on the face of
Jupiter from 8.06h to 10.16h GMT on June 9th. A small telescope at 100x or more should give a good view.
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.
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Saturn
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At magnitude +1.1 in Leo and with its rings tilting just
3š from edge on, Saturn is still visible as an evening object in the western sky.
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 is the first time since 1997 that the planetīs magnitude has faded to
this level.
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 are in 2009 and 2025.
Saturn's largest moon, Titan, is visible in small telescopes orbiting outside of the ring system.
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Uranus
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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.
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Neptune
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Neptune has an average magnitude of 7.9 which varies little with changing distance.
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Pluto
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Pluto reaches opposition on 23rd June in the constellation of
Sagittarius at a distance of 4,586 million kilometres (2,849 million miles).
No longer an offical planet and never brighter than 13 magnitude, Pluto is only visible through powerful
telescopes.
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Moon
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June
Full moon: 7th
Last quarter: 15th
New moon: 22nd
First quarter: 29th
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