The two planets, Jupiter and Mars, which will dominate our night sky for the second half of 2011 are now on view in the eastern sky before dawn. Indeed, Jupiter is unmistakable from the moment it rises in the ENE at 01:00 BST tomorrow and by midnight on the 27th.
Our chart looks east at 04:30 BST tomorrow and reaches from the horizon to some 60° in altitude. At that time tomorrow, the sky will be awash with the brightening dawn twilight. By the month’s end, though, the stars will be in the same place at 03:00 but the sky will be fully dark. Looking even further forward, the chart also applies at 01:00 BST at the start of September, 23:00 BST at the start of October and 20:00 GMT at the beginning of November.
The one aspect that does change is that Mars is speeding out of the picture. The arrow shows its motion over the coming month from its present position, 7° above and to the left of Aldebaran, eastwards between the horns of Taurus and into Gemini. By November it will be passing Regulus in Leo. During that time it brightens only a little from mag 1.4 to 1.0, but it will hit mag -1.2 when it stands directly opposite the Sun in the sky at opposition in Leo next March.
By far the most conspicuous object, though, is Jupiter which brightens from mag -2.3 to -2.9 by the time it reaches opposition in Aries on 29 October. It is then 594 million km distant, 179 million km closer than it is tomorrow. The planet is edging eastwards and has another 4° to go before it begins to retrograde westwards to its opposition point, not far from where it is now.
Jupiter is also the prime interest for telescope users. Its current diameter of 38 arcsec is big enough for small telescopes to show its changeable cloud bands. The usually dark South Equatorial Belt had faded to near-invisibility last year, but now appears to have fully recovered.
And, of course, the four main Jovian moons may be glimpsed through nothing more than binoculars as they alter their configuration to E and W of the disc from night to night. Mars, though, is only 4 arcsec wide at present, so glimpsing any detail at all is a real challenge.
Our chart also plots the radiant of the Perseids meteor shower which reaches its maximum on the morning of 13 August. Although its meteors appear in all parts of the sky, perspective means they appear to radiate away from this point.
The shower lasts from about 17 July to 24 August, but most Perseids arrive in just a few days around the peak. Sadly, the day of maximum coincides with the full moon, so the fainter meteors will be swamped by the moonlight. There should be plenty of bright ones, though, so it is well worth a look.