February 2009

Welcome to the latest newsletter which, we hope, you will enjoy reading it.

After around 11 pm, two stellar crosses are visible in the sky. The ‘true’ one, the Southern Cross, can be seen towards the southern horizon, while the False cross lies higher in the sky, above it. The bright star even higher than the False cross is Canopus, the second brightest star in the night sky. It is part of the Carinae constellation.

The Annual General Meeting was a well-attended event which was followed by an interesting and practical presentation on reading star maps by Steve Kleyn. Unfortunately, cloud meant that a real-world demonstration was not possible. However, members gained a very useful introduction to the sorts of star maps available both on the Internet or which can be bought and downloaded.

The monthly meetings will be held at 7 pm on Thursdays on the following days in 2009:

26 February (details below) 20 August
26 March 24 September
30 April 22 October
28 May 19 November
25 June 17 December
23 July

The February presentation will be made by Dr Ian Glass, a senior astronomer at the South African Astronomical Observatory in Cape Town. His topic is ‘Proxima, the nearest star (other than the Sun!), the title of his recently published book.

Following extensive consultation and discussion, the committee has agreed that the preferred site for the observatory is on municipal land at the eastern end of Rotary Way. The site is towards the Hemel en Aarde side of the brow of the mountain, which reduces the effect of light pollution from Hermanus. Members of the committee are currently writing a management plan and proposed budget for submission to Overstrand Municipality by the end of February, in time for consideration for the new financial year.

A second, smaller telescope has recently been kindly donated to the Club. It will be also be accommodated in the new observatory.

1. Is there a Planet X? If we know enough to say the solar system is a filigree construction, we might reasonably assume we know where all its bits are. However, lurking in the solar system’s dark recesses, rumour has it, is an unsighted world – Planet X, a frozen body perhaps as large as Mars, or even Earth. Planet X would be the most significant addition to the solar system since the discovery of Pluto. If Planet X does exist it could soon be uncovered (see Item 4).

2: How common are alien Earths – small, rocky planets orbiting at the right distance from their ‘sun’ to be not so hot that water boils and not so cold that it stays frozen? Until now, clues have been hard to come by, because surveys have not been sensitive enough to find many such planets. However, that should soon change thanks to the Kepler space telescope, which NASA is expecting to launch on 5 March. Its unique positioning in the solar system and unprecedented sensitivity mean that, for the first time, we will be able to see Earth-size planets in the “habitable zone” of their stars – the region where the temperature on the planet should be right for liquid water to exist at its surface.

3: A ‘small’ find. Astronomers have found an extrasolar planet with the smallest diameter yet measured – it is no more than twice as wide as Earth. The rocky body is also the fastest known, whipping around its star in less than a day. The planet, known as Exo-7b, lies about 390 light years away and orbits a star slightly smaller and cooler than the Sun. It was found by the French satellite COROT, which looks for the dimming caused when planets pass in front of, or transit, their parent stars.

4: Finding distant bodies. Over the past 20 years, huge swaths of the sky have been searched for slowly moving bodies, and well over 1000 Kuiper Belt objects (KBOs) found. However, these wide-area surveys can spot only large, bright objects; longer-exposure surveys that can find smaller, dimmer objects cover only small areas of the sky. A Mars-sized object at a distance of, say, 100 astronomical units (AUs) would be so faint that it could easily have escaped detection (An AU is the mean distance between the earth and the sun).

In December 2008, the first prototype of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) was brought into service at the Haleakala observatory on Maui, Hawaii. Soon, four telescopes – equipped with the world’s largest digital cameras, at 1.4 billion pixels apiece – will search the skies for anything that blinks or moves. Its main purpose is to look out for potentially hazardous asteroids bound for Earth, but inhabitants of the outer solar system will not escape its all-seeing eyes.

5: Who says size is not important? A dream is to be able to see extrasolar planets as small and as close to their host star as Earth is to the sun. That requires a telescope that can see objects nearly 3000 times smaller than those currently visible, and one that is not blinded by the host star’s light – feats that are not possible with even the largest telescope today, the 10.4-metre Gran Telescopio Canarias in Spain’s Canary Islands. However, in less than a decade, a trio of gigantic telescopes will be able to carry off the task with ease. The 24.5-metre Giant Magellan Telescope (GMT), the accurately named Thirty Meter Telescope (TMT) and the 42-metre European Extremely Large Telescope (E-ELT) will each collect enough light from these extrasolar planets to allow astronomers to study the composition of their atmospheres using spectroscopy. “Are there Earth-like planets in the habitable zones of nearby stars? That is one of the big questions we’d like to answer,” says Markus Kissler-Patig, who works on the E-ELT at the European Southern Observatory in Garching, Germany.

(News compiler’s footnote: And we poor amateur astronomers get quite excited at the prospect of looking through a 300 mm telecope??)

This month, our overview of the planets features Uranus and its moons.

Uranus, also known as Ouranos, discovered in 1781 by William Herschel,c was the embodiment of the sky or heavens, and known as the God of the Sky
It is four times the diameter of Earth, but its gaseous nature means it has a mass only 14.5 times greater than Earth. Uranus is the farthest planet that can be seen without a telescope.
It is an extraordinary in two particular ways. Firstly it rotates the opposite direction to most other planets and, secondly, it tilts 98 degrees, appearling to lie on its side. In other words, both its North and South poles face the Sun during its orbit.

Uranus also has a ring system like Saturn although nowhere near as large. There are eleven rings extending out from the planet, from 12,400 km’s above the surface to 25,600 km’s.

Its atmosphere consists of mainly hydrogen gas and to a far lesser degree helium and methane gas. Deeper, there is ice and a small, probably rocky, core.

Vital statistics:
Diameter: 51,500 km (32,000 miles)
Temperature: -197.15 C (-322.87° F)
Orbit: Takes 84 years to complete an orbit.
Average Distance: 2,870,972,200 km (1,783,939,400 miles – 19.2 AU) from Sun
Mass: 8.6849 x 1025 kg
Period of Rotation: 17.24 hours (retrograde: spins backwards compared to most other planets)
27 moons have discovered orbiting the planet. Unlike the majority of other moons in the Solar System, which have names of Greek or roman Gods, most of the moons of Uranus have been given names of characters from Shakespearian characters, including the following examples.

From Midsummer Nights Dream:
• Puck, at a distance of 86,010 km’s with a diameter of 162 km’s
• Titania, Uranus’ largest moon at a distance of 435,910 km from the planet with a diameter of 1,578 km’s.
• Oberon, at a distance of 583.520 km’s from the planet and with a diameter of 1,523 km’s.

From King Lear, the tiny moon Cordelia at a distance of 49,770 km’s and a diameter of just 40km’s.

From Hamlet, there is another very small moon Ophelia at a distance fo 53,790 km’s and a diameter of 42 km’s

From The Tempest:
• Ariel, at a distance of 191,020 km’s and a diameter of 1,162 km’s
• Miranda, at a distance of 129,390 km’s and a diameter of 480 km’s
• Caliban, which is way, way outside the main orbits of Uranus at a distance of 7.2 million km’s and a diameter of 96 km’s.
Reference: www.aerospaceguide.net

John Saunders (Chairman) 028 314 0543
Steve Kleyn (Technical Advisor) 028 312 2802
Pierre de Villiers (Treasurer) 028 313 0109
Irene Saunders (Secretary) 028 314 0543
Piet Daneel 028 314 0947
Pierre Hugo 028 312 1639
Jenny Morris 071 350 556

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