By Clive Jackson features@algarveresident.com
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. Soon after sunset, during the first week of the month when you look over towards the west, the bright planet Venus is still well visible in the constellation of Leo.
On the 9th of the month, Venus is close to the star Regulus, and on the 14th, the crescent Moon, three days past new, is below Venus. During July, Venus loses a little of its brightness as it moves lower in the evening sky.
The red planet Mars is also in the constellation of Leo but it is much fainter than Venus and on the evening of the 15th the crescent Moon will be seen below Mars.
The ringed planet Saturn is also fairly close to Mars this month in the constellation of Virgo and on the 16th the Moon will be close to it. Saturn is brighter than Mars so it should be easy to tell the two apart, with Mars having a pale orange colour and Saturn a Yellow tint.
On the 30th the pair are at their closest in the constellation of Virgo. One of the ways to tell planets from stars is that normally planets shine with a steady light and stars twinkle – this is true when they are high in the sky but less so when they are close to the horizon.
The giant planet Jupiter rises just after midnight by the end of the month and on the 31st the Moon is close. Jupiter is in the constellation of Pisces. Last month, one of the cloud belts of this gas giant planet disappeared; this has happened in the past and after a few weeks it came back.
Nobody knows exactly why this is so, but it may be a response to changes in the solar wind due to the slowdown in sun spot activity that has been observed recently.
Meteor shower
The last week in July sees the annual Capricornid Meteor shower, but this year the full Moon makes the night sky too bright to see all but the brightest meteors. If you are lucky to see very bright meteors, these are called fireballs and they can be quite spectacular passing right across the sky in just a few seconds often bright enough to cause a shadow and sometimes leaving a luminous trail behind.
On July 6, the Earth is at its furthest point in its orbit from the Sun, being three per cent further away than in December. This may not seem like a lot but it reduces the solar heating by six per cent and it may have an extreme effect as far as our long time climate is concerned as the Earth’s orbit varies much more than this on timescales of thousands of years. These variations are called Milankovitch Cycles and go a long way to explain why we have experienced an Ice Age every 100 thousand years for the past million years.
The last Ice Age started 100 thousand years ago. So, statistically speaking, we are due for the start of the next one any time now.
Of course, this planet’s climate is a deeply complex subject and nobody can predict exactly what’s going to happen in the years to come but there has been a rather chilly wind in the Algarve recently…
The Moon is at last quarter on the 4th, new on the 12th, first quarter on the 19th and full on the 26th.
To contact Clive Jackson, please telephone 281 322 527, fax 281 321 754, email: cdepa@mail.telepac.pt and website: www.cdepa.pt
