MERCURY is at inferior conjunction between the Sun and Earth on September 3. After conjunction the planet will be a morning object rising shortly before the Sun.

This appearance in the morning sky will be a very feeble affair, with Mercury never rising more than 40 minutes before the sun and so always being in strong twilight. This will make it just about impossible to ever see the planet. It will be a big contrast to the easy evening observation of Mercury possible during the second half of July and first part of August.

The planet is stationary on the 12th, less than 9 days after conjunction, and at its greatest distance 18° west of the sun on the 20th.

VENUS will be a very obvious object to the west in the evening sky throughout September. During the month it will set near 10 pm NZST: a little before 10 in the north and a little after in the south of NZ. The planet will set latest mid month.

Venus starts September one degree from Spica, the brightest star in Virgo. Venus will also be just over 4° Mars. On September 11 the three will be joined by the crescent moon which will be a little over 4° from each of the three. The graphic shows their relative positions looking to the west at 8pm.

Venus will be moving to the east through Virgo for most of September, gradually slowing during the second half of the month. Towards the end of the month, on the 25th the planet will cross into Libra.

MARS will be less than 4° below Spica on September 1, with Venus about a degree further away and slightly higher than the star.

Like Venus, Mars will be crossing Virgo during September and almost keeping pace with the far brighter planet, although their two paths will diverge a little. Mars will be a few degrees lower than Venus, as a result it will set about half an hour earlier. Mars crosses into Libra on September 27, two days after Venus.

The chart shows the moon, Venus, Mars and Spica as they appear in the sky to the west at 8 pm on September 11. The circle represents a field 5° in diameter a normal binocular view. A few of the brighter stars are also shown. Apart from Spica, only the two labelled with their magnitudes are likely to be visible to the unaided eye.

JUPITER will be readily visible in the evening throughout September. In early September it will be two or three hours after sunset before it is at a reasonable altitude between east and northeast. By the end of the month it will be readily visible once twilight fades.

Jupiter is at opposition on September 21, when it will rise close to the time of sunset and set close to the time of sunrise and be highest near midnight. At the same time it will be less than a degree from Uranus: they are in conjunction and slightly closer two days before on the 19th. The two planets are under a degree apart from September 13 to 25. Uranus will be an easy binocular object, at magnitude 5.7. In the evenings it will be to the left of Jupiter, changing from being slightly higher on the 13th to definitely lower on the 25th. Monitoring from night to night will readily show their relative motion.

The chart shows the relative paths of Jupiter and Uranus during September. It is orientated for about 9 pm. The circle shows a 5° field. Stars to magnitude 7 are shown, with those brighter than 6 labelled, without a decimal point.

On September 23, the day of the equinox, the two planets will be joined by the full moon. Jupiter and the moon will be just over 7° apart. Uranus will be in line between the two, much closer to Jupiter of course.

The conjunction of Jupiter and Uranus is the second this year with both planets at present moving in a retrograde (westerly) sense. Because it is nearer the Earth, Jupiter appears to move more quickly than Uranus even when moving backwards so is overtaking Uranus while in reverse. The third conjunction of the present series will take place on 4 January 2011.

SATURN will be a low object to the west in the early evening, almost directly below Venus. On the 1st it will set about 2 hours after the Sun. Each night during early September, Saturn will sink a little lower to become lost in the evening twilight by about the middle of the month. By then it will set little more than an hour after the Sun.

On the 10th the thin crescent Moon will be about 10° above Saturn, but by 45 minutes after sunset when the sky will be getting dark to see the planet, Saturn will be only about 6° above the horizon.