The May night sky.jpg

The May night sky

By CLIVE JACKSON [email protected]

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.

On the third of the month, the just after quarter Moon is close to the planet Saturn, this is a convenient pointer as Saturn is not very bright at the moment and just appears as an ordinary yellowish ‘star’ in the constellation of Leo.

From the fourth to the sixth the Eta-Aquarid Meteor shower will occur. This is a shower of ‘shooting stars’ that has been known about for many years; in fact the Chinese astronomers first recorded this in 401 A.D.  The dust given off from a comet on its orbit around the Sun causes this shower, as well as many others. The particular comet involved in the Eta-Aquarid is the well-known Halley’s Comet. This comet will not return now for many years but its dust is spread all around its orbit and causes the meteors every year at the same time.

On May 6, the close to full Moon passes below Spica, the bright star in the constellation of Virgo, and on the 10th when the full Moon rises in the constellation of Scorpius, the bright red star Antares will be just above the top edge of the Moon.

Well after midnight in the constellation of Capricorn, the giant planet Jupiter rises and, on the morning of the 17th the last quarter crescent Moon is close to the planet.

In the early evening in May, when the planet Saturn is high in the South, anyone looking towards the southern horizon can see the constellation of Centaurus, this constellation contains Alpha Centauri, the closest star to our solar system. This star is just below the horizon from southern Portugal, but if you travelled to the Canary Islands, this star, and also the constellation of the Southern Cross, would then be visible. 2000 years ago these objects would have been seen from the Algarve but the direction of the Earth’s axis is slowly altering over a 26,000 year period and we now have a slightly different view of the heavens than in the distant past.

In fact the sky changes all the time but in our life times we would not notice any difference. But over the centuries the positions of the stars change significantly and the night sky of Stone Age man for example would have been very different to the night sky of today. The star charts that define the Zodiacal constellations were drawn 2,000 years ago and depict the constellations in which the Sun passes through in its year long voyage across the sky. Originally there were 12 zodiacal constellations but now the sun passes through 13 constellations because in December it is in the constellation of Ophiuchus the Serpent Bearer. Also the Pole Star of today was not the Pole Star of the past and will not be the Pole Star of the future. In fact, in 12,000 years time, the axis of the Earth will point towards the constellation of Lyra and our Pole Star will be the very bright white star Vega.

The Moon is at First Quarter on May 1, full on May 9, Last Quarter on May 17 and New on the 24th, and also First Quarter again on May 31.

Clive Jackson can be contacted by phone on (00351) 281 321 754, by fax on (00351) 281 324 688, or by email to [email protected]. To visit his website, click on the link to the right of this page.