The Stars and Moon in June

in May 2011 - Southern Skies

The month starts with a new Moon. The first crescent will definitely be visible by the 3rd. Full Moon occurs on the 15th and there will be a lunar eclipse. An eclipse of the moon is safe to observe and can be enjoyed by all those who are able to see the Moon. For details see the accompanying box.

It’s also the winter solstice for us in the Southern Hemisphere, this occurs on 21 June. The solstice is the time of year when the Sun reaches its lowest point in our midday sky, a mere 33o above the northern horizon at midday, also making it the shortest day of the year. This is because the Earth’s South Pole is tilted furthest away from the Sun which is overhead of the Tropic of Cancer. It’s however not the time of latest sunrise and earliest sunset: the reason for this being that the Earth is not a regular time keeper due to the tilt of its axis and its elliptical orbit around the Sun. The earliest sunset is on the 12th and latest sunrise is on the 30th.

As we enter the winter months the evening sky becomes less spectacular to the casual observer. Orion has now all but disappeared from the evening sky; it makes its reappearance in the morning skies towards the end of the month, as does the small cluster of the Pleiades, or isiLimela – the ‘Digging Stars’. Our winter constellation, Scorpius is now in the east with the reddish giant star, Antares at its heart.

The Southern Cross is very high in the south and unmistakable with the two bright Pointers, Alpha and Beta Centauri on its left. The Milky Way stretches across the sky on either side of the Southern Cross. To the southwest, the second brightest star in the sky, Canopus is halfway up and continuing to the right is Sirius, the brightest star in the sky, low in the west. Procyon and Canis Minor are low in the northwest. Halfway up in the northern sky is Regulus – a bright, reddish star in Leo. Low in the northeast is Arcturus in the constellation of Bootes, the Herdsman. Above and to the right is the bright star Spica, in the constellation of Virgo.

During a lunar eclipse, or eclipse of the Moon, the Moon will first move into a part of the Earth’s shadow known as the penumbra, this is a region of partial shadow, and as the Moon moves into this, there is very little noticeable change. As the Moon moves further into the penumbra, it will appear to darken gradually. As it enters into the Earth’s total shadow, or umbra, the Moon will appear to change colour slowly, darken more and at the same time the curved part of the umbra will become visible on the Moon’s surface. Eventually the Moon enters totality. This is when the entire Moon is in the umbra, it appears at its darkest and reddest.

The Moon never really goes completely dark because some light gets bent (refracted) and scattered by the Earth’s atmosphere and still reaches the Moon’s surface. The coppery-red colour that the Moon takes on is due to the scattering of the Sun’s light as it passes through the Earth’s atmosphere. The amount of scattering that takes place depends on the amount of dust and other particles, or aerosols, in the atmosphere: the more there are, the redder the Moon will appear. At times when there has been a recent volcanic eruption, such as after Krakatoa, Mt. St Helens and Mt. Pinotuba, there would be a larger than normal amount of aerosols in the atmosphere and the Moon could then become a deep blood red colour: understandable that ancient people saw these eclipses as portents of death or doom!