The August night sky

By: Clive Jackson [email protected]

Director of the Astronomical Observatory of Tavira and the Camera Obscura, specialising in education and public outreach.

WELCOME TO the August night sky. At nightfall this month, Jupiter is the only bright planet visible, still close to the red giant star Antares in the constellation of Scorpius.

Jupiter is due south at sunset now and Saturn and Venus have now disappeared below the western horizon. Venus will pass between the Earth and the Sun in mid August and will not be visible.

If you do not mind staying up late, the planet Mars rises in the east an hour or so after midnight. On the morning of August 7, the Moon will pass through the Pleiades star cluster and just below is Mars in the constellation of Taurus.

A telescope will not show much detail on Mars as it is too far away at the moment and is covered in a dust storm that has blocked out our view of the surface. These dust storms are fairly common on Mars and can last many days.

On August 21, the nearly full Moon is close to Jupiter and on August 28 the full Moon will enter into the shadow of the Earth. This is called a Lunar Eclipse. Unfortunately this is not visible from Europe this time.

On the weekend of August 11 and 12, we have an opportunity to see the traditional peak of Perseids Meteor shower. This is made up from dust that was in the tail of a comet called Swift-Tuttle that was discovered in the 19th Century. The best time to see most of the meteors should be after midnight on August 12. With luck, you may see a meteor every minute or so. Nobody knows for sure the best time but this shower lasts for a week. You do not need a telescope just clear skies and lots of patience.

Our solar system has had thousands of comets orbiting the Sun since prehistoric times and all of them leave behind a trail of dust and gas. The gas rapidly disperses, but the dust can stay around for centuries and only slowly gets pushed out of orbit by sunlight pressure. These clouds of dust particles can bunch together sometimes, and when the Earth encounters this denser region we can experience a meteor storm with more than one ‘shooting stars’ visible per second. Normally, the rate is less than one per minute. These dust particles have typically a mass of less than one gram and this is sufficient to produce a brilliant streak of light in the night sky.

Meteors of this size never make it to the ground. Occasionally we encounter a rock weighing several kilos and this is sufficient to produce a spectacular fireball in the sky, and it may survive to hit the ground. When this happens the rock is called a meteorite. Approximately five hundred small meteorites hit the ground every year. In recent times there is no evidence of any fatalities due to meteorite impacts but two cars have been hit. Maybe this proves that cars cover more square metres of the Earth’s surface than people do!

The Moon is at Last Quarter on August 5, New on August 12, First Quarter on August 20 and full on August 28.