|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.
· 26th - Partial Eclipse of the Moon, visible from the Pacific Ocean, north America, Australasia and Asia.
· 26th - Pluto at opposition in Sagittarius.
· 28th - Mercury is at Superior Conjunction.
· The Moon: New - 12th, Full - 26th. Apogee (404,270 kilometres) - 3rd, Perigee (365,940 kilometres) - 15th.
Mercury remains visible in the eastern morning sky until the middle of June, for observors
in tropical and southern latitudes. For southern hemisphere observors, this is the most favourable morning apparition of 2010.
After the middle of the month, Mercury draws in towards the Sun and passes through superior conjunction
on 28th 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.
Venus remains a brilliant -4.0 magnitude in the western sky after sunset. The
planetīs northerly declination, as it moves through Gemini
means that is is much better placed for observors in Europe and North America than for those further south.
Early in the evening of June 15th, Venus and the three-day-old crescent Moon present a pretty spectacle in the western evening sky as dusk falls. On the
same evening Mars and Saturn are visible further east, although much fainter; the three planets with the Moon clearly marking the arc of the
ecliptic. Venus will be near the border between Gemini
and Cancer, the Moon will be in Cancer, Mars in
Leo and Saturn in Virgo.
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 continues to be visible in the evening sky but sets soon after midnight.
During June Mars is in Leo
, fading from +1.1 to +1.3 magnitude.
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 continues to be a conspicuous object in the early morning sky, moving through
Pisces, increasing in brightness from -2.3 to -2.5 magnitude during June. Observors in equatorial and
southern latitudes will have a much better view of the planet than those in Europe and North America.
Jupiter passes just 0.4šS of the planet Uranus (at magnitude +5.9) on the 8th June and is a useful guide to locating the fainter planet.
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 continues to be visible as an evening object in
Virgo, setting after midnight by the end of June. The planetīs ring angle is 2š and magnitude decreases from +1.0 to +1.1.
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 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.
Pluto reaches opposition on June 25th in the
constellation of Sagittarius, at a distance of 4,614 million kilometres (2,867 million miles) and magnitude +14.
No longer an offical planet and never brighter than +13 magnitude, Pluto is only visible through powerful telescopes.
Last quarter: 4th
New moon: 12th
First quarter: 19th
Full moon: 26th