September 2009
Star Struck - September 2009
In the early evening we find the winter Milky Way directly overhead, the great cloud of stars stretching from the southeast away to the north -west. Besides the Southern Cross (Crux) the most prominent constellations are Scorpius and Sagittarius. Scorpius traces an enormous question mark in the sky and is a constellation known for its many open and globular clusters. Sagittarius is most commonly recognised as the "Teapot", the stars for this asterism are in the shape of a bow with arrow drawn back. Sagittarius is where the centre of our Milky Way galaxy lies and is known for its many open clusters and knots of nebulosity or gas clouds
Globular clusters are spherical groupings of stars that are thought to number about 100,000 stars. Their numbers and masses are determined by mathematical deduction after observing the gravitational attractions within the clusters. These stars are of older generation and shine rather yellowish, similar to our Sun. There are around 100 globular clusters dotted around the night sky and they form a three dimensional spherical halo around the centre of the galaxy. These conclusions have been drawn by astronomers from both their positions and their perceived movements or proper motions. The southern night sky is favoured with the two most beautiful globular clusters of all, Omega Centauri, in Centaurus near Crux, and 47Tuc, in Tucana, the Toucan, appearing very close to the Small Magellanic cloud. A photo of 47 Tuc appears at right, and this is what you will see in any telescope with aperture form 150mm up. Omega Centauri is twice this size and on a moonless night is a naked eye object. Through any telescope it is a "wow" object and is worth searching out in the region just above the Pointers, alpha and beta Centauri, the two very bright stars just to the east of Crux that "point" to the Cross. Just next to the second brightest star in Crux, beta, or the left arm of the Cross, you can easily find the beautiful Jewel Box cluster with binoculars or small telescope. A photo appears to the left. The Jewel Box is known for its bright stars of many colours.
In Sagittarius, below the tail of Scorpius, we can also find half a dozen globular clusters around the "lid" of the teapot and a few of the most beautiful nebulae in our galaxy as well. Evocative names such as the Swan or Omega nebula, the Lagoon nebula and the Trifid nebula give only a hint at their beauty when seen on a good night with a moderate aperture, 200 mm or more. This area of sky is awash with deep sky objects and many can be located just by sweeping back and forth across the Milky Way and working from the zenith towards the southern horizon.
The planetary highlights in August are definitely Jupiter and Venus. Jupiter rises about 4PM and by 9PM is high in the eastern sky and clear of turbulent atmosphere, giving us stunning views of cloud bands and dancing moons. If you know where to look you can occasionally see Jupiter in the daylight! At this time of year we are perfectly aligned with the equator of this gas giant planet and are treated to what are known as mutual phenomena, or events where a couple of Jupiter's moons may not only transit the planet but can actually pass in front of each other as seen from Earth. On September 10th at 7PM two of Jupiters moons and one shadow will cross the face of the planet at the same time. Other moon and shadow events happen on Sept 17th and 24th. Venus is still the crystal bright white Morning Star, brightening the morning twilight hours for our early risers. It is much lower in the sky now, hovering just above the horizon. Saturn is not really visible as it is on the other side of the Sun( behind) in relation to the Earth. As September wears on Saturn will begin to appear in the early morning sky before dawn. If you can sneak a view through a telescope you will see that the "ring plane" is nearly edge on , a phenomenon that will not reappear for 14 years.
Speaking of passing behind something! In late June billions of people in India and across southern China saw the longest solar eclipse (6 minutes) thus far this century. It was the only total Solar Eclipse to occur this year and depending where the dateline fell was practically coincidental with the 40 year anniversary of man landing on the Moon! Hmmm! I wonder if the astrologers could make something from that!