The July night sky


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Clive Jackson is the Director of the Astronomical Observatory of Tavira (Sitio do Malhão, Tavira) and the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach.

WELCOME TO the July night sky. Since the Summer Solstice in June the temperatures have been rising and the cold wet spring is far behind us.

The nights are ideal for stargazing as the summer Milky Way is now visible in the evening sky, starting in the south and continuing overhead, and finally ending on the northern horizon.

On July 4 the Earth is at aphelion and this means it’s at its furthest away from the Sun in the slightly elliptical orbit that’s normal for planets. The difference is not a lot – only 3 per cent, but it does help to make our northern summers a little less hot than they would otherwise be. Over on the western horizon just after dark on July 6, the thin crescent Moon is close to Mars and Saturn in the constellation of Leo. And on July 10, Mars and Saturn will be at their closest together with a separation of around half a degree. In reality these two planets are not that close, in fact Saturn is more than a thousand million kilometres further away than Mars!

Four moons

Over in the south, soon after dark in the constellation of Sagittarius, Jupiter is now well visible. This planet is low down in the sky, but any telescope will show its four large moons. Jupiter is at its closest to Earth on July 9. On the night of July 16 the nearly full Moon is close to Jupiter.

Between the constellations of Sagittarius and Scorpius lies the heart of the Milky Way and this is where the centre of the galaxy hides behind millions of faint and distant stars. On a truly dark night the Milky Way can be seen to be interlaced with dark lanes and irregular shapes, these are clouds of star dust that are made during supernova explosions and will help to form sun like stars and solar systems in the future.

The Moon is New on July 3, First Quarter on July 10, full on July 18 and Last Quarter on July 25.