Welcome to the latest newsletter, and also to new member Deon Krige
The attachment is a short New Scientist article on vanishing matter.
As you might have read in the Hermanus Times or heard at the last meeting, we have become the 8th centre of the Astronomical Society of Southern Africa (ASSA), and the club is now officially Hermanus Astronomy Centre. We will be updating the logo and other identifiers soon. We look forward to accessing the large range of resources available through the ASSA.
Our signature constellation, the Southern Cross (Crux) is clearly visible to the south, and, later, overhead, at present. Of the two stars forming the Pointers, the one furthest away from the Cross is Alpha Centauri, the third brightest star in the sky after Sirius (Canis Major) and Canopus (Carinae).
CLUB MEETING – 26 MARCH
Centre members Pierre de Villers and Steve Kleyn gave an informative verbal and visual presentation on the techniques, challenges and rewards of astro-photography. They demonstrated that good quality images can be obtained using a standard digital camera, an understanding of digital photography, and digital processing.
FUTURE CLUB EVENINGS 2009
The monthly Thursday meetings will be held at 7 pm on the following days:
28 May (details below) 24 September
25 June 22 October
23 July 19 November
20 August 17 December
The topic for May’s meeting is ‘An introductory demonstration of web-based astronomy sites’. The presenter will be centre member, Derek Duckitt.
Cosmology interest group On 27 April, nine members attended a lively and informative discussion on the challenging topic of dark energy. The topic for discussion in May will be nucleoshynthesis.
Hermanus Magnetic Observatory John Saunders met the new Director of the HMO recently and they identified opportunities for future collaboration. The HAC is also to have an advertising corner at the HMO building.
Hermanus Primary School Hobbies Day The HAC stand was well-attended, with visitors able to watch DVD’s, look at two telescopes, talk to centre representatives, and browse through a range of information and literature. 20 people expressed an interest in joining the centre.
Wortelgat Outreach Trust Centre – Members have assisted Trust members in using their telescope, and plan to undertake training for their leaders.
OBSERVATORY COMMITTEE REPORT.
While the planning process continues, committee members are consolidating arrangements with existing collaborative fund-raisers eg. the Whale Festival Media & Marketing company., and approaching other potential sources of funding. Information on fund-raising strategies are outlined in the special observatory newsletter which was sent to centre members last month.
In addition to the external sources of funding being sought, the ‘Friends of the Observatory’ pledge campaign continues, with pledge forms for donations to help cover the costs of the planning process being available at the monthly centre meetings.
ASTRONOMY NEWS FROM STEVE KLEYN
1. Brown dwarfs may be more common than anyone thought. If so, it would change our idea of how stars form. In 2007, a star near the centre of our galaxy appeared to brighten because another object had focused the star’s light onto Earth. From the way the object bent the light, Andrew Gould of Ohio State University, and colleagues, identified it is a brown dwarf – a “failed star” with too little mass to sustain stellar nuclear reactions.
However, current estimates of how common brown dwarfs are suggest this finding is improbable – so either Gould struck lucky or brown dwarfs are more abundant than previously thought (www.arxiv.org/abs/0904.0249). If so, our models of how gas clouds collapse to form stars may be wrong, says Sebastien Lepine of the American Museum of Natural History, New York.
2. Most distant object in the universe spotted Astronomers have spotted this most distant object yet confirmed in the universe – a self-destructing star that exploded 13.1 billion light years from Earth. It detonated just 640 million years after the big bang, around the end of the cosmic “dark ages”, when the first stars and galaxies were lighting up space.
The object is a gamma-ray burst (GRB) – the brightest type of stellar explosion. GRBs occur when massive, spinning stars collapse to form black holes and spew out jets of gas at nearly the speed of light. These jets send gamma rays our way, along with “afterglows” at other wavelengths, which are produced when the jet heats up surrounding gas.
The burst, dubbed GRB 090423 for the date of its discovery, was originally spotted by NASA’s Swift satellite at 0755 GMT. Within an hour, astronomers began training ground-based telescopes on the same patch of sky to study the burst’s infrared afterglow. Some of the first observations were made on Mauna Kea in Hawaii with the United Kingdom Infrared Telescope and the Gemini North telescope. Other telescopes later measured the spectrum of the afterglow, revealing that the burst detonated about 13.1 billion light years from Earth. “It’s the most distant gamma-ray burst, but it’s also the most distant object in the universe overall,” says Edo Berger of the Harvard-Smithsonian Center for Astrophysics, a member of the team that observed the afterglow with Gemini North.
To gauge an object’s distance, astronomers measure how much an object’s light has been stretched, or reddened, by the expansion of space. This burst lies at a redshift of 8.2, more distant than the previous GRB record holder, which lay at a redshift of 6.7. Other astronomers have claimed to find galaxies at even greater distances – at redshifts of 10 and 9, but those findings are still ambiguous, says Joshua Bloom of the University of California, Berkeley, who observed the afterglow using the Gemini South telescope in Chile. Until now, the record holder for the farthest galaxy had a spectroscopically confirmed redshift of 6.96.
The burst’s immense distance makes the now-dead star the earliest object to be discovered from an era called ‘re-ionisation’, which occurred within the first billion years after the big bang. At that time, an obscuring fog of neutral hydrogen atoms was being burned off by radiation from the first stars and galaxies, and possibly also from the annihilation of dark matter particles.
“For astronomy, this is a watershed event,” Bloom told New Scientist. “This is the beginning of the study of the universe as it was before most of the structure that we know about today came into being.” The timing of the period of re-ionisation is still unclear, Bloom says. If astronomers can find more gamma-ray bursts at even greater distances, they could use their spectra to determine how quickly the universe became transparent and what was responsible for the process.
“In principle, you can see very early times in the universe [with GRBs], when everything else was too faint,” says Nial Tanvir of the University of Leicester in the UK, a member of a team that used the Very Large Telescope in Chile to make one of the first measurements of the distance of the burst. Distant blasts could also help pinpoint the locations of faint GRB host galaxies that could be detected by space telescopes like the soon-to-be-refurbished Hubble Space Telescope or NASA’s infrared James Webb Telescope, which is set to launch in 2013. However, building up a picture of the early universe will require finding many more distant bursts, and progress in discovering distant bursts has been slow. Swift has found 120 bursts with measured distances, but only three – including this one – date from the first billion years of the universe’s history. That is, in part, because stars did not form at high rates in the very early universe, before a redshift of about 5, and so they did not explode often as GRBs.
However, it is also because infrared detectors that are both sensitive and quick enough to measure very distant, short-lived GRB afterglows have only recently begun operating. As a result, astronomers may have missed out on identifying some of the most distant GRBs identified by Swift. Berger hopes the discovery of this object will hasten the development of new telescopes that could discover such afterglows with even greater efficiency. “As a single object, [the burst] is an amazing proof of concept,” says Berger. “I think we’ve shown that’s a worthwhile investment because [distant bursts] actually do exist.” NASA is considering one such telescope, called the Joint Astrophysics Nascent Universe Satellite (JANUS), for funding this year.
DID YOU KNOW?
In addition to the planets, we will also look at smaller objects found in the solar system. This month the focus is on asteroids and the asteroid belt.
The asteroid belt, located between Mars and Jupiter, is called the ‘main belt’ to distinguish it from other concentrations of minor planets eg. Kuiper belt, scattered disc. It is occupied by irregularly shaped asteroids or minor planets, most of which have relatively circular orbits.
Over half the mass in the belt is contained in the 4 largest objects – Ceres, Vesta, Pallas, Hygiea – all with mean diameters >400 km. Ceres has a diameter of around 950 km. Discovered in 1801, it was initially thought to be a planet. Having a crust, mantle and core, it is large enough for gravity to have rounded it, and is now classified as a dwarf planet. Remaining bodies in the belt range down to dust particles. The belt is estimated to have 1.1 – 1.9 million asteroids larger than 1 km diameter, and millions of smaller ones.
Although objects in the belt are thinly distributed, collisions can occur, forming an asteroid family, with members having similar orbits and composition. These make up 30 – 35% of the objects in the belt. The total mass of the asteroid belt is estimated to be about 4% of the mass of the Moon, with Ceres making up 32% of this and the other 3 large asteroids making up another 19%.
Asteroids are small solar system bodies, including minor planets, which orbit around the sun. Although the distinction between comets and asteroids is becoming blurred, the term ‘asteroid’ is commonly applied to objects in the inner solar system. The name means ‘star-like’ or ‘star-shaped’ (Greek). They are smaller than planets, but larger than meteoroids (see below).
Asteroids are thought to be the remnants of a proplanetary disc which was prevented from forming into a planet by the strong gravitational pull of Jupiter. Although newer, more expanded classification systems have been proposed, asteroids have tended to be classified into 3 types, according to their composition:
– C type (carbonaceous objects, making up 75% of known asteroids). Reddish
in colour, with low albedo (reflection of light from the sun), and mostly found in the outer parts of the belt
– S type (stony silicaceous objects – 17%). Mostly in the inner parts of the belt. They have relatively high albedo.
– M type (metallic – 8%). Mostly composed of iron-nickel.
Asteroids are also believed to contain traces of amino acids and other organic compounds, and some speculate that impacts with the early Earth were a source of the chemicals necessary for life
Vesta, with its high albedo, is the only asteroid visible to the naked eye.
Telescopes, including Hubble, can only provide fuzzy images of asteroids. The first close-up photographs of an asteroid were made in 1991 by the Galileo probe en route to Jupiter The first dedicated asteroid probe, NEAR Shoemaker, landed on an asteroid in 2001
Much research is currently being undertaken into the asteroid belt and other near-earth objects because of concerns about the possibility of collisions with Earth. This has increased the number of identified asteroids and led to greater knowledge of the orbits of larger objects. It has been suggested that, in the future, asteroids could become a source of minerals exhausted on Earth, or materials for use in construction of space habitats
Meteoroids are small sand to boulder sized particles of debris in the solar system. They are debris, mostly from asteroid collisions. When they enter Earth’s atmosphere, they are called meteors, becoming meteorites if they impact Earth’s surface. Meteorites are classified as stony (94%), iron (5%) or stony-iron 1%) It is estimated that around 500 meteorites ranging from marble to football size reach the surface of Earth annually
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
Pierre Hugo (Auditor & librarian) 028 312 1639
Jenny Morris (Newsletter editor) 071 350 5560
Derek Duckitt (IT & website co-ordinator) 082 414 4024
Johan Retief (Monthly sky maps) 028 315 1132
Piet Daneel 028 314 034